File: libgomp.info, Node: Top, Next: Enabling OpenMP, Up: (dir)
Introduction
************
This manual documents the usage of libgomp, the GNU Offloading and Multi
Processing Runtime Library. This includes the GNU implementation of the
OpenMP (http://www.openmp.org) Application Programming Interface (API)
for multi-platform shared-memory parallel programming in C/C++ and
Fortran, and the GNU implementation of the OpenACC
(https://www.openacc.org) Application Programming Interface (API) for
offloading of code to accelerator devices in C/C++ and Fortran.
Originally, libgomp implemented the GNU OpenMP Runtime Library.
Based on this, support for OpenACC and offloading (both OpenACC and
OpenMP 4's target construct) has been added later on, and the library's
name changed to GNU Offloading and Multi Processing Runtime Library.
* Menu:
* Enabling OpenMP:: How to enable OpenMP for your applications.
* Runtime Library Routines:: The OpenMP runtime application programming
interface.
* Environment Variables:: Influencing runtime behavior with environment
variables.
* Enabling OpenACC:: How to enable OpenACC for your
applications.
* OpenACC Runtime Library Routines:: The OpenACC runtime application
programming interface.
* OpenACC Environment Variables:: Influencing OpenACC runtime behavior with
environment variables.
* CUDA Streams Usage:: Notes on the implementation of
asynchronous operations.
* OpenACC Library Interoperability:: OpenACC library interoperability with the
NVIDIA CUBLAS library.
* The libgomp ABI:: Notes on the external ABI presented by libgomp.
* Reporting Bugs:: How to report bugs in the GNU Offloading and
Multi Processing Runtime Library.
* Copying:: GNU general public license says
how you can copy and share libgomp.
* GNU Free Documentation License::
How you can copy and share this manual.
* Funding:: How to help assure continued work for free
software.
* Library Index:: Index of this documentation.
File: libgomp.info, Node: Enabling OpenMP, Next: Runtime Library Routines, Prev: Top, Up: Top
1 Enabling OpenMP
*****************
To activate the OpenMP extensions for C/C++ and Fortran, the
compile-time flag '-fopenmp' must be specified. This enables the OpenMP
directive '#pragma omp' in C/C++ and '!$omp' directives in free form,
'c$omp', '*$omp' and '!$omp' directives in fixed form, '!$' conditional
compilation sentinels in free form and 'c$', '*$' and '!$' sentinels in
fixed form, for Fortran. The flag also arranges for automatic linking
of the OpenMP runtime library (*note Runtime Library Routines::).
A complete description of all OpenMP directives accepted may be found
in the OpenMP Application Program Interface (http://www.openmp.org)
manual, version 4.5.
File: libgomp.info, Node: Runtime Library Routines, Next: Environment Variables, Prev: Enabling OpenMP, Up: Top
2 Runtime Library Routines
**************************
The runtime routines described here are defined by Section 3 of the
OpenMP specification in version 4.5. The routines are structured in
following three parts:
* Menu:
Control threads, processors and the parallel environment. They have C
linkage, and do not throw exceptions.
* omp_get_active_level:: Number of active parallel regions
* omp_get_ancestor_thread_num:: Ancestor thread ID
* omp_get_cancellation:: Whether cancellation support is enabled
* omp_get_default_device:: Get the default device for target regions
* omp_get_dynamic:: Dynamic teams setting
* omp_get_level:: Number of parallel regions
* omp_get_max_active_levels:: Maximum number of active regions
* omp_get_max_task_priority:: Maximum task priority value that can be set
* omp_get_max_threads:: Maximum number of threads of parallel region
* omp_get_nested:: Nested parallel regions
* omp_get_num_devices:: Number of target devices
* omp_get_num_procs:: Number of processors online
* omp_get_num_teams:: Number of teams
* omp_get_num_threads:: Size of the active team
* omp_get_proc_bind:: Whether theads may be moved between CPUs
* omp_get_schedule:: Obtain the runtime scheduling method
* omp_get_team_num:: Get team number
* omp_get_team_size:: Number of threads in a team
* omp_get_thread_limit:: Maximum number of threads
* omp_get_thread_num:: Current thread ID
* omp_in_parallel:: Whether a parallel region is active
* omp_in_final:: Whether in final or included task region
* omp_is_initial_device:: Whether executing on the host device
* omp_set_default_device:: Set the default device for target regions
* omp_set_dynamic:: Enable/disable dynamic teams
* omp_set_max_active_levels:: Limits the number of active parallel regions
* omp_set_nested:: Enable/disable nested parallel regions
* omp_set_num_threads:: Set upper team size limit
* omp_set_schedule:: Set the runtime scheduling method
Initialize, set, test, unset and destroy simple and nested locks.
* omp_init_lock:: Initialize simple lock
* omp_set_lock:: Wait for and set simple lock
* omp_test_lock:: Test and set simple lock if available
* omp_unset_lock:: Unset simple lock
* omp_destroy_lock:: Destroy simple lock
* omp_init_nest_lock:: Initialize nested lock
* omp_set_nest_lock:: Wait for and set simple lock
* omp_test_nest_lock:: Test and set nested lock if available
* omp_unset_nest_lock:: Unset nested lock
* omp_destroy_nest_lock:: Destroy nested lock
Portable, thread-based, wall clock timer.
* omp_get_wtick:: Get timer precision.
* omp_get_wtime:: Elapsed wall clock time.
File: libgomp.info, Node: omp_get_active_level, Next: omp_get_ancestor_thread_num, Up: Runtime Library Routines
2.1 'omp_get_active_level' - Number of parallel regions
=======================================================
_Description_:
This function returns the nesting level for the active parallel
blocks, which enclose the calling call.
_C/C++_
_Prototype_: 'int omp_get_active_level(void);'
_Fortran_:
_Interface_: 'integer function omp_get_active_level()'
_See also_:
*note omp_get_level::, *note omp_get_max_active_levels::, *note
omp_set_max_active_levels::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.20.
File: libgomp.info, Node: omp_get_ancestor_thread_num, Next: omp_get_cancellation, Prev: omp_get_active_level, Up: Runtime Library Routines
2.2 'omp_get_ancestor_thread_num' - Ancestor thread ID
======================================================
_Description_:
This function returns the thread identification number for the
given nesting level of the current thread. For values of LEVEL
outside zero to 'omp_get_level' -1 is returned; if LEVEL is
'omp_get_level' the result is identical to 'omp_get_thread_num'.
_C/C++_
_Prototype_: 'int omp_get_ancestor_thread_num(int level);'
_Fortran_:
_Interface_: 'integer function omp_get_ancestor_thread_num(level)'
'integer level'
_See also_:
*note omp_get_level::, *note omp_get_thread_num::, *note
omp_get_team_size::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.18.
File: libgomp.info, Node: omp_get_cancellation, Next: omp_get_default_device, Prev: omp_get_ancestor_thread_num, Up: Runtime Library Routines
2.3 'omp_get_cancellation' - Whether cancellation support is enabled
====================================================================
_Description_:
This function returns 'true' if cancellation is activated, 'false'
otherwise. Here, 'true' and 'false' represent their
language-specific counterparts. Unless 'OMP_CANCELLATION' is set
true, cancellations are deactivated.
_C/C++_:
_Prototype_: 'int omp_get_cancellation(void);'
_Fortran_:
_Interface_: 'logical function omp_get_cancellation()'
_See also_:
*note OMP_CANCELLATION::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.9.
File: libgomp.info, Node: omp_get_default_device, Next: omp_get_dynamic, Prev: omp_get_cancellation, Up: Runtime Library Routines
2.4 'omp_get_default_device' - Get the default device for target regions
========================================================================
_Description_:
Get the default device for target regions without device clause.
_C/C++_:
_Prototype_: 'int omp_get_default_device(void);'
_Fortran_:
_Interface_: 'integer function omp_get_default_device()'
_See also_:
*note OMP_DEFAULT_DEVICE::, *note omp_set_default_device::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.30.
File: libgomp.info, Node: omp_get_dynamic, Next: omp_get_level, Prev: omp_get_default_device, Up: Runtime Library Routines
2.5 'omp_get_dynamic' - Dynamic teams setting
=============================================
_Description_:
This function returns 'true' if enabled, 'false' otherwise. Here,
'true' and 'false' represent their language-specific counterparts.
The dynamic team setting may be initialized at startup by the
'OMP_DYNAMIC' environment variable or at runtime using
'omp_set_dynamic'. If undefined, dynamic adjustment is disabled by
default.
_C/C++_:
_Prototype_: 'int omp_get_dynamic(void);'
_Fortran_:
_Interface_: 'logical function omp_get_dynamic()'
_See also_:
*note omp_set_dynamic::, *note OMP_DYNAMIC::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.8.
File: libgomp.info, Node: omp_get_level, Next: omp_get_max_active_levels, Prev: omp_get_dynamic, Up: Runtime Library Routines
2.6 'omp_get_level' - Obtain the current nesting level
======================================================
_Description_:
This function returns the nesting level for the parallel blocks,
which enclose the calling call.
_C/C++_
_Prototype_: 'int omp_get_level(void);'
_Fortran_:
_Interface_: 'integer function omp_level()'
_See also_:
*note omp_get_active_level::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.17.
File: libgomp.info, Node: omp_get_max_active_levels, Next: omp_get_max_task_priority, Prev: omp_get_level, Up: Runtime Library Routines
2.7 'omp_get_max_active_levels' - Maximum number of active regions
==================================================================
_Description_:
This function obtains the maximum allowed number of nested, active
parallel regions.
_C/C++_
_Prototype_: 'int omp_get_max_active_levels(void);'
_Fortran_:
_Interface_: 'integer function omp_get_max_active_levels()'
_See also_:
*note omp_set_max_active_levels::, *note omp_get_active_level::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.16.
File: libgomp.info, Node: omp_get_max_task_priority, Next: omp_get_max_threads, Prev: omp_get_max_active_levels, Up: Runtime Library Routines
2.8 'omp_get_max_task_priority' - Maximum priority value
========================================================
that can be set for tasks.
_Description_:
This function obtains the maximum allowed priority number for
tasks.
_C/C++_
_Prototype_: 'int omp_get_max_task_priority(void);'
_Fortran_:
_Interface_: 'integer function omp_get_max_task_priority()'
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.29.
File: libgomp.info, Node: omp_get_max_threads, Next: omp_get_nested, Prev: omp_get_max_task_priority, Up: Runtime Library Routines
2.9 'omp_get_max_threads' - Maximum number of threads of parallel region
========================================================================
_Description_:
Return the maximum number of threads used for the current parallel
region that does not use the clause 'num_threads'.
_C/C++_:
_Prototype_: 'int omp_get_max_threads(void);'
_Fortran_:
_Interface_: 'integer function omp_get_max_threads()'
_See also_:
*note omp_set_num_threads::, *note omp_set_dynamic::, *note
omp_get_thread_limit::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.3.
File: libgomp.info, Node: omp_get_nested, Next: omp_get_num_devices, Prev: omp_get_max_threads, Up: Runtime Library Routines
2.10 'omp_get_nested' - Nested parallel regions
===============================================
_Description_:
This function returns 'true' if nested parallel regions are
enabled, 'false' otherwise. Here, 'true' and 'false' represent
their language-specific counterparts.
Nested parallel regions may be initialized at startup by the
'OMP_NESTED' environment variable or at runtime using
'omp_set_nested'. If undefined, nested parallel regions are
disabled by default.
_C/C++_:
_Prototype_: 'int omp_get_nested(void);'
_Fortran_:
_Interface_: 'logical function omp_get_nested()'
_See also_:
*note omp_set_nested::, *note OMP_NESTED::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.11.
File: libgomp.info, Node: omp_get_num_devices, Next: omp_get_num_procs, Prev: omp_get_nested, Up: Runtime Library Routines
2.11 'omp_get_num_devices' - Number of target devices
=====================================================
_Description_:
Returns the number of target devices.
_C/C++_:
_Prototype_: 'int omp_get_num_devices(void);'
_Fortran_:
_Interface_: 'integer function omp_get_num_devices()'
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.31.
File: libgomp.info, Node: omp_get_num_procs, Next: omp_get_num_teams, Prev: omp_get_num_devices, Up: Runtime Library Routines
2.12 'omp_get_num_procs' - Number of processors online
======================================================
_Description_:
Returns the number of processors online on that device.
_C/C++_:
_Prototype_: 'int omp_get_num_procs(void);'
_Fortran_:
_Interface_: 'integer function omp_get_num_procs()'
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.5.
File: libgomp.info, Node: omp_get_num_teams, Next: omp_get_num_threads, Prev: omp_get_num_procs, Up: Runtime Library Routines
2.13 'omp_get_num_teams' - Number of teams
==========================================
_Description_:
Returns the number of teams in the current team region.
_C/C++_:
_Prototype_: 'int omp_get_num_teams(void);'
_Fortran_:
_Interface_: 'integer function omp_get_num_teams()'
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.32.
File: libgomp.info, Node: omp_get_num_threads, Next: omp_get_proc_bind, Prev: omp_get_num_teams, Up: Runtime Library Routines
2.14 'omp_get_num_threads' - Size of the active team
====================================================
_Description_:
Returns the number of threads in the current team. In a sequential
section of the program 'omp_get_num_threads' returns 1.
The default team size may be initialized at startup by the
'OMP_NUM_THREADS' environment variable. At runtime, the size of
the current team may be set either by the 'NUM_THREADS' clause or
by 'omp_set_num_threads'. If none of the above were used to define
a specific value and 'OMP_DYNAMIC' is disabled, one thread per CPU
online is used.
_C/C++_:
_Prototype_: 'int omp_get_num_threads(void);'
_Fortran_:
_Interface_: 'integer function omp_get_num_threads()'
_See also_:
*note omp_get_max_threads::, *note omp_set_num_threads::, *note
OMP_NUM_THREADS::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.2.
File: libgomp.info, Node: omp_get_proc_bind, Next: omp_get_schedule, Prev: omp_get_num_threads, Up: Runtime Library Routines
2.15 'omp_get_proc_bind' - Whether theads may be moved between CPUs
===================================================================
_Description_:
This functions returns the currently active thread affinity policy,
which is set via 'OMP_PROC_BIND'. Possible values are
'omp_proc_bind_false', 'omp_proc_bind_true',
'omp_proc_bind_master', 'omp_proc_bind_close' and
'omp_proc_bind_spread'.
_C/C++_:
_Prototype_: 'omp_proc_bind_t omp_get_proc_bind(void);'
_Fortran_:
_Interface_: 'integer(kind=omp_proc_bind_kind) function
omp_get_proc_bind()'
_See also_:
*note OMP_PROC_BIND::, *note OMP_PLACES::, *note
GOMP_CPU_AFFINITY::,
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.22.
File: libgomp.info, Node: omp_get_schedule, Next: omp_get_team_num, Prev: omp_get_proc_bind, Up: Runtime Library Routines
2.16 'omp_get_schedule' - Obtain the runtime scheduling method
==============================================================
_Description_:
Obtain the runtime scheduling method. The KIND argument will be
set to the value 'omp_sched_static', 'omp_sched_dynamic',
'omp_sched_guided' or 'omp_sched_auto'. The second argument,
CHUNK_SIZE, is set to the chunk size.
_C/C++_
_Prototype_: 'void omp_get_schedule(omp_sched_t *kind, int
*chunk_size);'
_Fortran_:
_Interface_: 'subroutine omp_get_schedule(kind, chunk_size)'
'integer(kind=omp_sched_kind) kind'
'integer chunk_size'
_See also_:
*note omp_set_schedule::, *note OMP_SCHEDULE::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.13.
File: libgomp.info, Node: omp_get_team_num, Next: omp_get_team_size, Prev: omp_get_schedule, Up: Runtime Library Routines
2.17 'omp_get_team_num' - Get team number
=========================================
_Description_:
Returns the team number of the calling thread.
_C/C++_:
_Prototype_: 'int omp_get_team_num(void);'
_Fortran_:
_Interface_: 'integer function omp_get_team_num()'
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.33.
File: libgomp.info, Node: omp_get_team_size, Next: omp_get_thread_limit, Prev: omp_get_team_num, Up: Runtime Library Routines
2.18 'omp_get_team_size' - Number of threads in a team
======================================================
_Description_:
This function returns the number of threads in a thread team to
which either the current thread or its ancestor belongs. For
values of LEVEL outside zero to 'omp_get_level', -1 is returned; if
LEVEL is zero, 1 is returned, and for 'omp_get_level', the result
is identical to 'omp_get_num_threads'.
_C/C++_:
_Prototype_: 'int omp_get_team_size(int level);'
_Fortran_:
_Interface_: 'integer function omp_get_team_size(level)'
'integer level'
_See also_:
*note omp_get_num_threads::, *note omp_get_level::, *note
omp_get_ancestor_thread_num::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.19.
File: libgomp.info, Node: omp_get_thread_limit, Next: omp_get_thread_num, Prev: omp_get_team_size, Up: Runtime Library Routines
2.19 'omp_get_thread_limit' - Maximum number of threads
=======================================================
_Description_:
Return the maximum number of threads of the program.
_C/C++_:
_Prototype_: 'int omp_get_thread_limit(void);'
_Fortran_:
_Interface_: 'integer function omp_get_thread_limit()'
_See also_:
*note omp_get_max_threads::, *note OMP_THREAD_LIMIT::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.14.
File: libgomp.info, Node: omp_get_thread_num, Next: omp_in_parallel, Prev: omp_get_thread_limit, Up: Runtime Library Routines
2.20 'omp_get_thread_num' - Current thread ID
=============================================
_Description_:
Returns a unique thread identification number within the current
team. In a sequential parts of the program, 'omp_get_thread_num'
always returns 0. In parallel regions the return value varies from
0 to 'omp_get_num_threads'-1 inclusive. The return value of the
master thread of a team is always 0.
_C/C++_:
_Prototype_: 'int omp_get_thread_num(void);'
_Fortran_:
_Interface_: 'integer function omp_get_thread_num()'
_See also_:
*note omp_get_num_threads::, *note omp_get_ancestor_thread_num::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.4.
File: libgomp.info, Node: omp_in_parallel, Next: omp_in_final, Prev: omp_get_thread_num, Up: Runtime Library Routines
2.21 'omp_in_parallel' - Whether a parallel region is active
============================================================
_Description_:
This function returns 'true' if currently running in parallel,
'false' otherwise. Here, 'true' and 'false' represent their
language-specific counterparts.
_C/C++_:
_Prototype_: 'int omp_in_parallel(void);'
_Fortran_:
_Interface_: 'logical function omp_in_parallel()'
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.6.
File: libgomp.info, Node: omp_in_final, Next: omp_is_initial_device, Prev: omp_in_parallel, Up: Runtime Library Routines
2.22 'omp_in_final' - Whether in final or included task region
==============================================================
_Description_:
This function returns 'true' if currently running in a final or
included task region, 'false' otherwise. Here, 'true' and 'false'
represent their language-specific counterparts.
_C/C++_:
_Prototype_: 'int omp_in_final(void);'
_Fortran_:
_Interface_: 'logical function omp_in_final()'
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.21.
File: libgomp.info, Node: omp_is_initial_device, Next: omp_set_default_device, Prev: omp_in_final, Up: Runtime Library Routines
2.23 'omp_is_initial_device' - Whether executing on the host device
===================================================================
_Description_:
This function returns 'true' if currently running on the host
device, 'false' otherwise. Here, 'true' and 'false' represent
their language-specific counterparts.
_C/C++_:
_Prototype_: 'int omp_is_initial_device(void);'
_Fortran_:
_Interface_: 'logical function omp_is_initial_device()'
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.34.
File: libgomp.info, Node: omp_set_default_device, Next: omp_set_dynamic, Prev: omp_is_initial_device, Up: Runtime Library Routines
2.24 'omp_set_default_device' - Set the default device for target regions
=========================================================================
_Description_:
Set the default device for target regions without device clause.
The argument shall be a nonnegative device number.
_C/C++_:
_Prototype_: 'void omp_set_default_device(int device_num);'
_Fortran_:
_Interface_: 'subroutine omp_set_default_device(device_num)'
'integer device_num'
_See also_:
*note OMP_DEFAULT_DEVICE::, *note omp_get_default_device::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.29.
File: libgomp.info, Node: omp_set_dynamic, Next: omp_set_max_active_levels, Prev: omp_set_default_device, Up: Runtime Library Routines
2.25 'omp_set_dynamic' - Enable/disable dynamic teams
=====================================================
_Description_:
Enable or disable the dynamic adjustment of the number of threads
within a team. The function takes the language-specific equivalent
of 'true' and 'false', where 'true' enables dynamic adjustment of
team sizes and 'false' disables it.
_C/C++_:
_Prototype_: 'void omp_set_dynamic(int dynamic_threads);'
_Fortran_:
_Interface_: 'subroutine omp_set_dynamic(dynamic_threads)'
'logical, intent(in) :: dynamic_threads'
_See also_:
*note OMP_DYNAMIC::, *note omp_get_dynamic::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.7.
File: libgomp.info, Node: omp_set_max_active_levels, Next: omp_set_nested, Prev: omp_set_dynamic, Up: Runtime Library Routines
2.26 'omp_set_max_active_levels' - Limits the number of active parallel regions
===============================================================================
_Description_:
This function limits the maximum allowed number of nested, active
parallel regions.
_C/C++_
_Prototype_: 'void omp_set_max_active_levels(int max_levels);'
_Fortran_:
_Interface_: 'subroutine omp_set_max_active_levels(max_levels)'
'integer max_levels'
_See also_:
*note omp_get_max_active_levels::, *note omp_get_active_level::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.15.
File: libgomp.info, Node: omp_set_nested, Next: omp_set_num_threads, Prev: omp_set_max_active_levels, Up: Runtime Library Routines
2.27 'omp_set_nested' - Enable/disable nested parallel regions
==============================================================
_Description_:
Enable or disable nested parallel regions, i.e., whether team
members are allowed to create new teams. The function takes the
language-specific equivalent of 'true' and 'false', where 'true'
enables dynamic adjustment of team sizes and 'false' disables it.
_C/C++_:
_Prototype_: 'void omp_set_nested(int nested);'
_Fortran_:
_Interface_: 'subroutine omp_set_nested(nested)'
'logical, intent(in) :: nested'
_See also_:
*note OMP_NESTED::, *note omp_get_nested::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.10.
File: libgomp.info, Node: omp_set_num_threads, Next: omp_set_schedule, Prev: omp_set_nested, Up: Runtime Library Routines
2.28 'omp_set_num_threads' - Set upper team size limit
======================================================
_Description_:
Specifies the number of threads used by default in subsequent
parallel sections, if those do not specify a 'num_threads' clause.
The argument of 'omp_set_num_threads' shall be a positive integer.
_C/C++_:
_Prototype_: 'void omp_set_num_threads(int num_threads);'
_Fortran_:
_Interface_: 'subroutine omp_set_num_threads(num_threads)'
'integer, intent(in) :: num_threads'
_See also_:
*note OMP_NUM_THREADS::, *note omp_get_num_threads::, *note
omp_get_max_threads::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.1.
File: libgomp.info, Node: omp_set_schedule, Next: omp_init_lock, Prev: omp_set_num_threads, Up: Runtime Library Routines
2.29 'omp_set_schedule' - Set the runtime scheduling method
===========================================================
_Description_:
Sets the runtime scheduling method. The KIND argument can have the
value 'omp_sched_static', 'omp_sched_dynamic', 'omp_sched_guided'
or 'omp_sched_auto'. Except for 'omp_sched_auto', the chunk size
is set to the value of CHUNK_SIZE if positive, or to the default
value if zero or negative. For 'omp_sched_auto' the CHUNK_SIZE
argument is ignored.
_C/C++_
_Prototype_: 'void omp_set_schedule(omp_sched_t kind, int
chunk_size);'
_Fortran_:
_Interface_: 'subroutine omp_set_schedule(kind, chunk_size)'
'integer(kind=omp_sched_kind) kind'
'integer chunk_size'
_See also_:
*note omp_get_schedule:: *note OMP_SCHEDULE::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.2.12.
File: libgomp.info, Node: omp_init_lock, Next: omp_set_lock, Prev: omp_set_schedule, Up: Runtime Library Routines
2.30 'omp_init_lock' - Initialize simple lock
=============================================
_Description_:
Initialize a simple lock. After initialization, the lock is in an
unlocked state.
_C/C++_:
_Prototype_: 'void omp_init_lock(omp_lock_t *lock);'
_Fortran_:
_Interface_: 'subroutine omp_init_lock(svar)'
'integer(omp_lock_kind), intent(out) :: svar'
_See also_:
*note omp_destroy_lock::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.3.1.
File: libgomp.info, Node: omp_set_lock, Next: omp_test_lock, Prev: omp_init_lock, Up: Runtime Library Routines
2.31 'omp_set_lock' - Wait for and set simple lock
==================================================
_Description_:
Before setting a simple lock, the lock variable must be initialized
by 'omp_init_lock'. The calling thread is blocked until the lock
is available. If the lock is already held by the current thread, a
deadlock occurs.
_C/C++_:
_Prototype_: 'void omp_set_lock(omp_lock_t *lock);'
_Fortran_:
_Interface_: 'subroutine omp_set_lock(svar)'
'integer(omp_lock_kind), intent(inout) :: svar'
_See also_:
*note omp_init_lock::, *note omp_test_lock::, *note
omp_unset_lock::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.3.4.
File: libgomp.info, Node: omp_test_lock, Next: omp_unset_lock, Prev: omp_set_lock, Up: Runtime Library Routines
2.32 'omp_test_lock' - Test and set simple lock if available
============================================================
_Description_:
Before setting a simple lock, the lock variable must be initialized
by 'omp_init_lock'. Contrary to 'omp_set_lock', 'omp_test_lock'
does not block if the lock is not available. This function returns
'true' upon success, 'false' otherwise. Here, 'true' and 'false'
represent their language-specific counterparts.
_C/C++_:
_Prototype_: 'int omp_test_lock(omp_lock_t *lock);'
_Fortran_:
_Interface_: 'logical function omp_test_lock(svar)'
'integer(omp_lock_kind), intent(inout) :: svar'
_See also_:
*note omp_init_lock::, *note omp_set_lock::, *note omp_set_lock::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.3.6.
File: libgomp.info, Node: omp_unset_lock, Next: omp_destroy_lock, Prev: omp_test_lock, Up: Runtime Library Routines
2.33 'omp_unset_lock' - Unset simple lock
=========================================
_Description_:
A simple lock about to be unset must have been locked by
'omp_set_lock' or 'omp_test_lock' before. In addition, the lock
must be held by the thread calling 'omp_unset_lock'. Then, the
lock becomes unlocked. If one or more threads attempted to set the
lock before, one of them is chosen to, again, set the lock to
itself.
_C/C++_:
_Prototype_: 'void omp_unset_lock(omp_lock_t *lock);'
_Fortran_:
_Interface_: 'subroutine omp_unset_lock(svar)'
'integer(omp_lock_kind), intent(inout) :: svar'
_See also_:
*note omp_set_lock::, *note omp_test_lock::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.3.5.
File: libgomp.info, Node: omp_destroy_lock, Next: omp_init_nest_lock, Prev: omp_unset_lock, Up: Runtime Library Routines
2.34 'omp_destroy_lock' - Destroy simple lock
=============================================
_Description_:
Destroy a simple lock. In order to be destroyed, a simple lock
must be in the unlocked state.
_C/C++_:
_Prototype_: 'void omp_destroy_lock(omp_lock_t *lock);'
_Fortran_:
_Interface_: 'subroutine omp_destroy_lock(svar)'
'integer(omp_lock_kind), intent(inout) :: svar'
_See also_:
*note omp_init_lock::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.3.3.
File: libgomp.info, Node: omp_init_nest_lock, Next: omp_set_nest_lock, Prev: omp_destroy_lock, Up: Runtime Library Routines
2.35 'omp_init_nest_lock' - Initialize nested lock
==================================================
_Description_:
Initialize a nested lock. After initialization, the lock is in an
unlocked state and the nesting count is set to zero.
_C/C++_:
_Prototype_: 'void omp_init_nest_lock(omp_nest_lock_t *lock);'
_Fortran_:
_Interface_: 'subroutine omp_init_nest_lock(nvar)'
'integer(omp_nest_lock_kind), intent(out) :: nvar'
_See also_:
*note omp_destroy_nest_lock::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.3.1.
File: libgomp.info, Node: omp_set_nest_lock, Next: omp_test_nest_lock, Prev: omp_init_nest_lock, Up: Runtime Library Routines
2.36 'omp_set_nest_lock' - Wait for and set nested lock
=======================================================
_Description_:
Before setting a nested lock, the lock variable must be initialized
by 'omp_init_nest_lock'. The calling thread is blocked until the
lock is available. If the lock is already held by the current
thread, the nesting count for the lock is incremented.
_C/C++_:
_Prototype_: 'void omp_set_nest_lock(omp_nest_lock_t *lock);'
_Fortran_:
_Interface_: 'subroutine omp_set_nest_lock(nvar)'
'integer(omp_nest_lock_kind), intent(inout) :: nvar'
_See also_:
*note omp_init_nest_lock::, *note omp_unset_nest_lock::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.3.4.
File: libgomp.info, Node: omp_test_nest_lock, Next: omp_unset_nest_lock, Prev: omp_set_nest_lock, Up: Runtime Library Routines
2.37 'omp_test_nest_lock' - Test and set nested lock if available
=================================================================
_Description_:
Before setting a nested lock, the lock variable must be initialized
by 'omp_init_nest_lock'. Contrary to 'omp_set_nest_lock',
'omp_test_nest_lock' does not block if the lock is not available.
If the lock is already held by the current thread, the new nesting
count is returned. Otherwise, the return value equals zero.
_C/C++_:
_Prototype_: 'int omp_test_nest_lock(omp_nest_lock_t *lock);'
_Fortran_:
_Interface_: 'logical function omp_test_nest_lock(nvar)'
'integer(omp_nest_lock_kind), intent(inout) :: nvar'
_See also_:
*note omp_init_lock::, *note omp_set_lock::, *note omp_set_lock::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.3.6.
File: libgomp.info, Node: omp_unset_nest_lock, Next: omp_destroy_nest_lock, Prev: omp_test_nest_lock, Up: Runtime Library Routines
2.38 'omp_unset_nest_lock' - Unset nested lock
==============================================
_Description_:
A nested lock about to be unset must have been locked by
'omp_set_nested_lock' or 'omp_test_nested_lock' before. In
addition, the lock must be held by the thread calling
'omp_unset_nested_lock'. If the nesting count drops to zero, the
lock becomes unlocked. If one ore more threads attempted to set
the lock before, one of them is chosen to, again, set the lock to
itself.
_C/C++_:
_Prototype_: 'void omp_unset_nest_lock(omp_nest_lock_t *lock);'
_Fortran_:
_Interface_: 'subroutine omp_unset_nest_lock(nvar)'
'integer(omp_nest_lock_kind), intent(inout) :: nvar'
_See also_:
*note omp_set_nest_lock::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.3.5.
File: libgomp.info, Node: omp_destroy_nest_lock, Next: omp_get_wtick, Prev: omp_unset_nest_lock, Up: Runtime Library Routines
2.39 'omp_destroy_nest_lock' - Destroy nested lock
==================================================
_Description_:
Destroy a nested lock. In order to be destroyed, a nested lock
must be in the unlocked state and its nesting count must equal
zero.
_C/C++_:
_Prototype_: 'void omp_destroy_nest_lock(omp_nest_lock_t *);'
_Fortran_:
_Interface_: 'subroutine omp_destroy_nest_lock(nvar)'
'integer(omp_nest_lock_kind), intent(inout) :: nvar'
_See also_:
*note omp_init_lock::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.3.3.
File: libgomp.info, Node: omp_get_wtick, Next: omp_get_wtime, Prev: omp_destroy_nest_lock, Up: Runtime Library Routines
2.40 'omp_get_wtick' - Get timer precision
==========================================
_Description_:
Gets the timer precision, i.e., the number of seconds between two
successive clock ticks.
_C/C++_:
_Prototype_: 'double omp_get_wtick(void);'
_Fortran_:
_Interface_: 'double precision function omp_get_wtick()'
_See also_:
*note omp_get_wtime::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.4.2.
File: libgomp.info, Node: omp_get_wtime, Prev: omp_get_wtick, Up: Runtime Library Routines
2.41 'omp_get_wtime' - Elapsed wall clock time
==============================================
_Description_:
Elapsed wall clock time in seconds. The time is measured per
thread, no guarantee can be made that two distinct threads measure
the same time. Time is measured from some "time in the past",
which is an arbitrary time guaranteed not to change during the
execution of the program.
_C/C++_:
_Prototype_: 'double omp_get_wtime(void);'
_Fortran_:
_Interface_: 'double precision function omp_get_wtime()'
_See also_:
*note omp_get_wtick::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 3.4.1.
File: libgomp.info, Node: Environment Variables, Next: Enabling OpenACC, Prev: Runtime Library Routines, Up: Top
3 Environment Variables
***********************
The environment variables which beginning with 'OMP_' are defined by
section 4 of the OpenMP specification in version 4.5, while those
beginning with 'GOMP_' are GNU extensions.
* Menu:
* OMP_CANCELLATION:: Set whether cancellation is activated
* OMP_DISPLAY_ENV:: Show OpenMP version and environment variables
* OMP_DEFAULT_DEVICE:: Set the device used in target regions
* OMP_DYNAMIC:: Dynamic adjustment of threads
* OMP_MAX_ACTIVE_LEVELS:: Set the maximum number of nested parallel regions
* OMP_MAX_TASK_PRIORITY:: Set the maximum task priority value
* OMP_NESTED:: Nested parallel regions
* OMP_NUM_THREADS:: Specifies the number of threads to use
* OMP_PROC_BIND:: Whether theads may be moved between CPUs
* OMP_PLACES:: Specifies on which CPUs the theads should be placed
* OMP_STACKSIZE:: Set default thread stack size
* OMP_SCHEDULE:: How threads are scheduled
* OMP_THREAD_LIMIT:: Set the maximum number of threads
* OMP_WAIT_POLICY:: How waiting threads are handled
* GOMP_CPU_AFFINITY:: Bind threads to specific CPUs
* GOMP_DEBUG:: Enable debugging output
* GOMP_STACKSIZE:: Set default thread stack size
* GOMP_SPINCOUNT:: Set the busy-wait spin count
* GOMP_RTEMS_THREAD_POOLS:: Set the RTEMS specific thread pools
File: libgomp.info, Node: OMP_CANCELLATION, Next: OMP_DISPLAY_ENV, Up: Environment Variables
3.1 'OMP_CANCELLATION' - Set whether cancellation is activated
==============================================================
_Description_:
If set to 'TRUE', the cancellation is activated. If set to 'FALSE'
or if unset, cancellation is disabled and the 'cancel' construct is
ignored.
_See also_:
*note omp_get_cancellation::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.11
File: libgomp.info, Node: OMP_DISPLAY_ENV, Next: OMP_DEFAULT_DEVICE, Prev: OMP_CANCELLATION, Up: Environment Variables
3.2 'OMP_DISPLAY_ENV' - Show OpenMP version and environment variables
=====================================================================
_Description_:
If set to 'TRUE', the OpenMP version number and the values
associated with the OpenMP environment variables are printed to
'stderr'. If set to 'VERBOSE', it additionally shows the value of
the environment variables which are GNU extensions. If undefined
or set to 'FALSE', this information will not be shown.
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.12
File: libgomp.info, Node: OMP_DEFAULT_DEVICE, Next: OMP_DYNAMIC, Prev: OMP_DISPLAY_ENV, Up: Environment Variables
3.3 'OMP_DEFAULT_DEVICE' - Set the device used in target regions
================================================================
_Description_:
Set to choose the device which is used in a 'target' region, unless
the value is overridden by 'omp_set_default_device' or by a
'device' clause. The value shall be the nonnegative device number.
If no device with the given device number exists, the code is
executed on the host. If unset, device number 0 will be used.
_See also_:
*note omp_get_default_device::, *note omp_set_default_device::,
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.13
File: libgomp.info, Node: OMP_DYNAMIC, Next: OMP_MAX_ACTIVE_LEVELS, Prev: OMP_DEFAULT_DEVICE, Up: Environment Variables
3.4 'OMP_DYNAMIC' - Dynamic adjustment of threads
=================================================
_Description_:
Enable or disable the dynamic adjustment of the number of threads
within a team. The value of this environment variable shall be
'TRUE' or 'FALSE'. If undefined, dynamic adjustment is disabled by
default.
_See also_:
*note omp_set_dynamic::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.3
File: libgomp.info, Node: OMP_MAX_ACTIVE_LEVELS, Next: OMP_MAX_TASK_PRIORITY, Prev: OMP_DYNAMIC, Up: Environment Variables
3.5 'OMP_MAX_ACTIVE_LEVELS' - Set the maximum number of nested parallel regions
===============================================================================
_Description_:
Specifies the initial value for the maximum number of nested
parallel regions. The value of this variable shall be a positive
integer. If undefined, the number of active levels is unlimited.
_See also_:
*note omp_set_max_active_levels::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.9
File: libgomp.info, Node: OMP_MAX_TASK_PRIORITY, Next: OMP_NESTED, Prev: OMP_MAX_ACTIVE_LEVELS, Up: Environment Variables
3.6 'OMP_MAX_TASK_PRIORITY' - Set the maximum priority
======================================================
number that can be set for a task.
_Description_:
Specifies the initial value for the maximum priority value that can
be set for a task. The value of this variable shall be a
non-negative integer, and zero is allowed. If undefined, the
default priority is 0.
_See also_:
*note omp_get_max_task_priority::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.14
File: libgomp.info, Node: OMP_NESTED, Next: OMP_NUM_THREADS, Prev: OMP_MAX_TASK_PRIORITY, Up: Environment Variables
3.7 'OMP_NESTED' - Nested parallel regions
==========================================
_Description_:
Enable or disable nested parallel regions, i.e., whether team
members are allowed to create new teams. The value of this
environment variable shall be 'TRUE' or 'FALSE'. If undefined,
nested parallel regions are disabled by default.
_See also_:
*note omp_set_nested::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.6
File: libgomp.info, Node: OMP_NUM_THREADS, Next: OMP_PROC_BIND, Prev: OMP_NESTED, Up: Environment Variables
3.8 'OMP_NUM_THREADS' - Specifies the number of threads to use
==============================================================
_Description_:
Specifies the default number of threads to use in parallel regions.
The value of this variable shall be a comma-separated list of
positive integers; the value specified the number of threads to use
for the corresponding nested level. If undefined one thread per
CPU is used.
_See also_:
*note omp_set_num_threads::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.2
File: libgomp.info, Node: OMP_PROC_BIND, Next: OMP_PLACES, Prev: OMP_NUM_THREADS, Up: Environment Variables
3.9 'OMP_PROC_BIND' - Whether theads may be moved between CPUs
==============================================================
_Description_:
Specifies whether threads may be moved between processors. If set
to 'TRUE', OpenMP theads should not be moved; if set to 'FALSE'
they may be moved. Alternatively, a comma separated list with the
values 'MASTER', 'CLOSE' and 'SPREAD' can be used to specify the
thread affinity policy for the corresponding nesting level. With
'MASTER' the worker threads are in the same place partition as the
master thread. With 'CLOSE' those are kept close to the master
thread in contiguous place partitions. And with 'SPREAD' a sparse
distribution across the place partitions is used.
When undefined, 'OMP_PROC_BIND' defaults to 'TRUE' when
'OMP_PLACES' or 'GOMP_CPU_AFFINITY' is set and 'FALSE' otherwise.
_See also_:
*note OMP_PLACES::, *note GOMP_CPU_AFFINITY::, *note
omp_get_proc_bind::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.4
File: libgomp.info, Node: OMP_PLACES, Next: OMP_STACKSIZE, Prev: OMP_PROC_BIND, Up: Environment Variables
3.10 'OMP_PLACES' - Specifies on which CPUs the theads should be placed
=======================================================================
_Description_:
The thread placement can be either specified using an abstract name
or by an explicit list of the places. The abstract names
'threads', 'cores' and 'sockets' can be optionally followed by a
positive number in parentheses, which denotes the how many places
shall be created. With 'threads' each place corresponds to a
single hardware thread; 'cores' to a single core with the
corresponding number of hardware threads; and with 'sockets' the
place corresponds to a single socket. The resulting placement can
be shown by setting the 'OMP_DISPLAY_ENV' environment variable.
Alternatively, the placement can be specified explicitly as
comma-separated list of places. A place is specified by set of
nonnegative numbers in curly braces, denoting the denoting the
hardware threads. The hardware threads belonging to a place can
either be specified as comma-separated list of nonnegative thread
numbers or using an interval. Multiple places can also be either
specified by a comma-separated list of places or by an interval.
To specify an interval, a colon followed by the count is placed
after after the hardware thread number or the place. Optionally,
the length can be followed by a colon and the stride number -
otherwise a unit stride is assumed. For instance, the following
specifies the same places list: '"{0,1,2}, {3,4,6}, {7,8,9},
{10,11,12}"'; '"{0:3}, {3:3}, {7:3}, {10:3}"'; and '"{0:2}:4:3"'.
If 'OMP_PLACES' and 'GOMP_CPU_AFFINITY' are unset and
'OMP_PROC_BIND' is either unset or 'false', threads may be moved
between CPUs following no placement policy.
_See also_:
*note OMP_PROC_BIND::, *note GOMP_CPU_AFFINITY::, *note
omp_get_proc_bind::, *note OMP_DISPLAY_ENV::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.5
File: libgomp.info, Node: OMP_STACKSIZE, Next: OMP_SCHEDULE, Prev: OMP_PLACES, Up: Environment Variables
3.11 'OMP_STACKSIZE' - Set default thread stack size
====================================================
_Description_:
Set the default thread stack size in kilobytes, unless the number
is suffixed by 'B', 'K', 'M' or 'G', in which case the size is,
respectively, in bytes, kilobytes, megabytes or gigabytes. This is
different from 'pthread_attr_setstacksize' which gets the number of
bytes as an argument. If the stack size cannot be set due to
system constraints, an error is reported and the initial stack size
is left unchanged. If undefined, the stack size is system
dependent.
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.7
File: libgomp.info, Node: OMP_SCHEDULE, Next: OMP_THREAD_LIMIT, Prev: OMP_STACKSIZE, Up: Environment Variables
3.12 'OMP_SCHEDULE' - How threads are scheduled
===============================================
_Description_:
Allows to specify 'schedule type' and 'chunk size'. The value of
the variable shall have the form: 'type[,chunk]' where 'type' is
one of 'static', 'dynamic', 'guided' or 'auto' The optional 'chunk'
size shall be a positive integer. If undefined, dynamic scheduling
and a chunk size of 1 is used.
_See also_:
*note omp_set_schedule::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Sections
2.7.1.1 and 4.1
File: libgomp.info, Node: OMP_THREAD_LIMIT, Next: OMP_WAIT_POLICY, Prev: OMP_SCHEDULE, Up: Environment Variables
3.13 'OMP_THREAD_LIMIT' - Set the maximum number of threads
===========================================================
_Description_:
Specifies the number of threads to use for the whole program. The
value of this variable shall be a positive integer. If undefined,
the number of threads is not limited.
_See also_:
*note OMP_NUM_THREADS::, *note omp_get_thread_limit::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.10
File: libgomp.info, Node: OMP_WAIT_POLICY, Next: GOMP_CPU_AFFINITY, Prev: OMP_THREAD_LIMIT, Up: Environment Variables
3.14 'OMP_WAIT_POLICY' - How waiting threads are handled
========================================================
_Description_:
Specifies whether waiting threads should be active or passive. If
the value is 'PASSIVE', waiting threads should not consume CPU
power while waiting; while the value is 'ACTIVE' specifies that
they should. If undefined, threads wait actively for a short time
before waiting passively.
_See also_:
*note GOMP_SPINCOUNT::
_Reference_:
OpenMP specification v4.5 (http://www.openmp.org/), Section 4.8
File: libgomp.info, Node: GOMP_CPU_AFFINITY, Next: GOMP_DEBUG, Prev: OMP_WAIT_POLICY, Up: Environment Variables
3.15 'GOMP_CPU_AFFINITY' - Bind threads to specific CPUs
========================================================
_Description_:
Binds threads to specific CPUs. The variable should contain a
space-separated or comma-separated list of CPUs. This list may
contain different kinds of entries: either single CPU numbers in
any order, a range of CPUs (M-N) or a range with some stride
(M-N:S). CPU numbers are zero based. For example,
'GOMP_CPU_AFFINITY="0 3 1-2 4-15:2"' will bind the initial thread
to CPU 0, the second to CPU 3, the third to CPU 1, the fourth to
CPU 2, the fifth to CPU 4, the sixth through tenth to CPUs 6, 8,
10, 12, and 14 respectively and then start assigning back from the
beginning of the list. 'GOMP_CPU_AFFINITY=0' binds all threads to
CPU 0.
There is no libgomp library routine to determine whether a CPU
affinity specification is in effect. As a workaround,
language-specific library functions, e.g., 'getenv' in C or
'GET_ENVIRONMENT_VARIABLE' in Fortran, may be used to query the
setting of the 'GOMP_CPU_AFFINITY' environment variable. A defined
CPU affinity on startup cannot be changed or disabled during the
runtime of the application.
If both 'GOMP_CPU_AFFINITY' and 'OMP_PROC_BIND' are set,
'OMP_PROC_BIND' has a higher precedence. If neither has been set
and 'OMP_PROC_BIND' is unset, or when 'OMP_PROC_BIND' is set to
'FALSE', the host system will handle the assignment of threads to
CPUs.
_See also_:
*note OMP_PLACES::, *note OMP_PROC_BIND::
File: libgomp.info, Node: GOMP_DEBUG, Next: GOMP_STACKSIZE, Prev: GOMP_CPU_AFFINITY, Up: Environment Variables
3.16 'GOMP_DEBUG' - Enable debugging output
===========================================
_Description_:
Enable debugging output. The variable should be set to '0'
(disabled, also the default if not set), or '1' (enabled).
If enabled, some debugging output will be printed during execution.
This is currently not specified in more detail, and subject to
change.
File: libgomp.info, Node: GOMP_STACKSIZE, Next: GOMP_SPINCOUNT, Prev: GOMP_DEBUG, Up: Environment Variables
3.17 'GOMP_STACKSIZE' - Set default thread stack size
=====================================================
_Description_:
Set the default thread stack size in kilobytes. This is different
from 'pthread_attr_setstacksize' which gets the number of bytes as
an argument. If the stack size cannot be set due to system
constraints, an error is reported and the initial stack size is
left unchanged. If undefined, the stack size is system dependent.
_See also_:
*note OMP_STACKSIZE::
_Reference_:
GCC Patches Mailinglist
(http://gcc.gnu.org/ml/gcc-patches/2006-06/msg00493.html), GCC
Patches Mailinglist
(http://gcc.gnu.org/ml/gcc-patches/2006-06/msg00496.html)
File: libgomp.info, Node: GOMP_SPINCOUNT, Next: GOMP_RTEMS_THREAD_POOLS, Prev: GOMP_STACKSIZE, Up: Environment Variables
3.18 'GOMP_SPINCOUNT' - Set the busy-wait spin count
====================================================
_Description_:
Determines how long a threads waits actively with consuming CPU
power before waiting passively without consuming CPU power. The
value may be either 'INFINITE', 'INFINITY' to always wait actively
or an integer which gives the number of spins of the busy-wait
loop. The integer may optionally be followed by the following
suffixes acting as multiplication factors: 'k' (kilo, thousand),
'M' (mega, million), 'G' (giga, billion), or 'T' (tera, trillion).
If undefined, 0 is used when 'OMP_WAIT_POLICY' is 'PASSIVE',
300,000 is used when 'OMP_WAIT_POLICY' is undefined and 30 billion
is used when 'OMP_WAIT_POLICY' is 'ACTIVE'. If there are more
OpenMP threads than available CPUs, 1000 and 100 spins are used for
'OMP_WAIT_POLICY' being 'ACTIVE' or undefined, respectively; unless
the 'GOMP_SPINCOUNT' is lower or 'OMP_WAIT_POLICY' is 'PASSIVE'.
_See also_:
*note OMP_WAIT_POLICY::
File: libgomp.info, Node: GOMP_RTEMS_THREAD_POOLS, Prev: GOMP_SPINCOUNT, Up: Environment Variables
3.19 'GOMP_RTEMS_THREAD_POOLS' - Set the RTEMS specific thread pools
====================================================================
_Description_:
This environment variable is only used on the RTEMS real-time
operating system. It determines the scheduler instance specific
thread pools. The format for 'GOMP_RTEMS_THREAD_POOLS' is a list
of optional '<thread-pool-count>[$<priority>]@<scheduler-name>'
configurations separated by ':' where:
* '<thread-pool-count>' is the thread pool count for this
scheduler instance.
* '$<priority>' is an optional priority for the worker threads
of a thread pool according to 'pthread_setschedparam'. In
case a priority value is omitted, then a worker thread will
inherit the priority of the OpenMP master thread that created
it. The priority of the worker thread is not changed after
creation, even if a new OpenMP master thread using the worker
has a different priority.
* '@<scheduler-name>' is the scheduler instance name according
to the RTEMS application configuration.
In case no thread pool configuration is specified for a scheduler
instance, then each OpenMP master thread of this scheduler instance
will use its own dynamically allocated thread pool. To limit the
worker thread count of the thread pools, each OpenMP master thread
must call 'omp_set_num_threads'.
_Example_:
Lets suppose we have three scheduler instances 'IO', 'WRK0', and
'WRK1' with 'GOMP_RTEMS_THREAD_POOLS' set to '"1@WRK0:3$4@WRK1"'.
Then there are no thread pool restrictions for scheduler instance
'IO'. In the scheduler instance 'WRK0' there is one thread pool
available. Since no priority is specified for this scheduler
instance, the worker thread inherits the priority of the OpenMP
master thread that created it. In the scheduler instance 'WRK1'
there are three thread pools available and their worker threads run
at priority four.
File: libgomp.info, Node: Enabling OpenACC, Next: OpenACC Runtime Library Routines, Prev: Environment Variables, Up: Top
4 Enabling OpenACC
******************
To activate the OpenACC extensions for C/C++ and Fortran, the
compile-time flag '-fopenacc' must be specified. This enables the
OpenACC directive '#pragma acc' in C/C++ and '!$accp' directives in free
form, 'c$acc', '*$acc' and '!$acc' directives in fixed form, '!$'
conditional compilation sentinels in free form and 'c$', '*$' and '!$'
sentinels in fixed form, for Fortran. The flag also arranges for
automatic linking of the OpenACC runtime library (*note OpenACC Runtime
Library Routines::).
A complete description of all OpenACC directives accepted may be
found in the OpenACC (https://www.openacc.org) Application Programming
Interface manual, version 2.0.
Note that this is an experimental feature and subject to change in
future versions of GCC. See <https://gcc.gnu.org/wiki/OpenACC>; for more
information.
File: libgomp.info, Node: OpenACC Runtime Library Routines, Next: OpenACC Environment Variables, Prev: Enabling OpenACC, Up: Top
5 OpenACC Runtime Library Routines
**********************************
The runtime routines described here are defined by section 3 of the
OpenACC specifications in version 2.0. They have C linkage, and do not
throw exceptions. Generally, they are available only for the host, with
the exception of 'acc_on_device', which is available for both the host
and the acceleration device.
* Menu:
* acc_get_num_devices:: Get number of devices for the given device
type.
* acc_set_device_type:: Set type of device accelerator to use.
* acc_get_device_type:: Get type of device accelerator to be used.
* acc_set_device_num:: Set device number to use.
* acc_get_device_num:: Get device number to be used.
* acc_async_test:: Tests for completion of a specific asynchronous
operation.
* acc_async_test_all:: Tests for completion of all asychronous
operations.
* acc_wait:: Wait for completion of a specific asynchronous
operation.
* acc_wait_all:: Waits for completion of all asyncrhonous
operations.
* acc_wait_all_async:: Wait for completion of all asynchronous
operations.
* acc_wait_async:: Wait for completion of asynchronous operations.
* acc_init:: Initialize runtime for a specific device type.
* acc_shutdown:: Shuts down the runtime for a specific device
type.
* acc_on_device:: Whether executing on a particular device
* acc_malloc:: Allocate device memory.
* acc_free:: Free device memory.
* acc_copyin:: Allocate device memory and copy host memory to
it.
* acc_present_or_copyin:: If the data is not present on the device,
allocate device memory and copy from host
memory.
* acc_create:: Allocate device memory and map it to host
memory.
* acc_present_or_create:: If the data is not present on the device,
allocate device memory and map it to host
memory.
* acc_copyout:: Copy device memory to host memory.
* acc_delete:: Free device memory.
* acc_update_device:: Update device memory from mapped host memory.
* acc_update_self:: Update host memory from mapped device memory.
* acc_map_data:: Map previously allocated device memory to host
memory.
* acc_unmap_data:: Unmap device memory from host memory.
* acc_deviceptr:: Get device pointer associated with specific
host address.
* acc_hostptr:: Get host pointer associated with specific
device address.
* acc_is_present:: Indiciate whether host variable / array is
present on device.
* acc_memcpy_to_device:: Copy host memory to device memory.
* acc_memcpy_from_device:: Copy device memory to host memory.
API routines for target platforms.
* acc_get_current_cuda_device:: Get CUDA device handle.
* acc_get_current_cuda_context::Get CUDA context handle.
* acc_get_cuda_stream:: Get CUDA stream handle.
* acc_set_cuda_stream:: Set CUDA stream handle.
File: libgomp.info, Node: acc_get_num_devices, Next: acc_set_device_type, Up: OpenACC Runtime Library Routines
5.1 'acc_get_num_devices' - Get number of devices for given device type
=======================================================================
_Description_
This function returns a value indicating the number of devices
available for the device type specified in DEVICETYPE.
_C/C++_:
_Prototype_: 'int acc_get_num_devices(acc_device_t devicetype);'
_Fortran_:
_Interface_: 'integer function acc_get_num_devices(devicetype)'
'integer(kind=acc_device_kind) devicetype'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.1.
File: libgomp.info, Node: acc_set_device_type, Next: acc_get_device_type, Prev: acc_get_num_devices, Up: OpenACC Runtime Library Routines
5.2 'acc_set_device_type' - Set type of device accelerator to use.
==================================================================
_Description_
This function indicates to the runtime library which device typr,
specified in DEVICETYPE, to use when executing a parallel or
kernels region.
_C/C++_:
_Prototype_: 'acc_set_device_type(acc_device_t devicetype);'
_Fortran_:
_Interface_: 'subroutine acc_set_device_type(devicetype)'
'integer(kind=acc_device_kind) devicetype'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.2.
File: libgomp.info, Node: acc_get_device_type, Next: acc_set_device_num, Prev: acc_set_device_type, Up: OpenACC Runtime Library Routines
5.3 'acc_get_device_type' - Get type of device accelerator to be used.
======================================================================
_Description_
This function returns what device type will be used when executing
a parallel or kernels region.
_C/C++_:
_Prototype_: 'acc_device_t acc_get_device_type(void);'
_Fortran_:
_Interface_: 'function acc_get_device_type(void)'
'integer(kind=acc_device_kind) acc_get_device_type'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.3.
File: libgomp.info, Node: acc_set_device_num, Next: acc_get_device_num, Prev: acc_get_device_type, Up: OpenACC Runtime Library Routines
5.4 'acc_set_device_num' - Set device number to use.
====================================================
_Description_
This function will indicate to the runtime which device number,
specified by NUM, associated with the specifed device type
DEVICETYPE.
_C/C++_:
_Prototype_: 'acc_set_device_num(int num, acc_device_t devicetype);'
_Fortran_:
_Interface_: 'subroutine acc_set_device_num(devicenum, devicetype)'
'integer devicenum'
'integer(kind=acc_device_kind) devicetype'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.4.
File: libgomp.info, Node: acc_get_device_num, Next: acc_async_test, Prev: acc_set_device_num, Up: OpenACC Runtime Library Routines
5.5 'acc_get_device_num' - Get device number to be used.
========================================================
_Description_
This function returns which device number associated with the
specified device type DEVICETYPE, will be used when executing a
parallel or kernels region.
_C/C++_:
_Prototype_: 'int acc_get_device_num(acc_device_t devicetype);'
_Fortran_:
_Interface_: 'function acc_get_device_num(devicetype)'
'integer(kind=acc_device_kind) devicetype'
'integer acc_get_device_num'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.5.
File: libgomp.info, Node: acc_async_test, Next: acc_async_test_all, Prev: acc_get_device_num, Up: OpenACC Runtime Library Routines
5.6 'acc_async_test' - Test for completion of a specific asynchronous operation.
================================================================================
_Description_
This function tests for completion of the asynchrounous operation
specified in ARG. In C/C++, a non-zero value will be returned to
indicate the specified asynchronous operation has completed. While
Fortran will return a 'true'. If the asynchrounous operation has
not completed, C/C++ returns a zero and Fortran returns a 'false'.
_C/C++_:
_Prototype_: 'int acc_async_test(int arg);'
_Fortran_:
_Interface_: 'function acc_async_test(arg)'
'integer(kind=acc_handle_kind) arg'
'logical acc_async_test'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.6.
File: libgomp.info, Node: acc_async_test_all, Next: acc_wait, Prev: acc_async_test, Up: OpenACC Runtime Library Routines
5.7 'acc_async_test_all' - Tests for completion of all asynchronous operations.
===============================================================================
_Description_
This function tests for completion of all asynchrounous operations.
In C/C++, a non-zero value will be returned to indicate all
asynchronous operations have completed. While Fortran will return
a 'true'. If any asynchronous operation has not completed, C/C++
returns a zero and Fortran returns a 'false'.
_C/C++_:
_Prototype_: 'int acc_async_test_all(void);'
_Fortran_:
_Interface_: 'function acc_async_test()'
'logical acc_get_device_num'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.7.
File: libgomp.info, Node: acc_wait, Next: acc_wait_all, Prev: acc_async_test_all, Up: OpenACC Runtime Library Routines
5.8 'acc_wait' - Wait for completion of a specific asynchronous operation.
==========================================================================
_Description_
This function waits for completion of the asynchronous operation
specified in ARG.
_C/C++_:
_Prototype_: 'acc_wait(arg);'
_Prototype 'acc_async_wait(arg);'
(OpenACC 1.0
compatibility)_:
_Fortran_:
_Interface_: 'subroutine acc_wait(arg)'
'integer(acc_handle_kind) arg'
_Interface 'subroutine acc_async_wait(arg)'
(OpenACC 1.0
compatibility)_:
'integer(acc_handle_kind) arg'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.8.
File: libgomp.info, Node: acc_wait_all, Next: acc_wait_all_async, Prev: acc_wait, Up: OpenACC Runtime Library Routines
5.9 'acc_wait_all' - Waits for completion of all asynchronous operations.
=========================================================================
_Description_
This function waits for the completion of all asynchronous
operations.
_C/C++_:
_Prototype_: 'acc_wait_all(void);'
_Prototype 'acc_async_wait_all(void);'
(OpenACC 1.0
compatibility)_:
_Fortran_:
_Interface_: 'subroutine acc_wait_all()'
_Interface 'subroutine acc_async_wait_all()'
(OpenACC 1.0
compatibility)_:
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.10.
File: libgomp.info, Node: acc_wait_all_async, Next: acc_wait_async, Prev: acc_wait_all, Up: OpenACC Runtime Library Routines
5.10 'acc_wait_all_async' - Wait for completion of all asynchronous operations.
===============================================================================
_Description_
This function enqueues a wait operation on the queue ASYNC for any
and all asynchronous operations that have been previously enqueued
on any queue.
_C/C++_:
_Prototype_: 'acc_wait_all_async(int async);'
_Fortran_:
_Interface_: 'subroutine acc_wait_all_async(async)'
'integer(acc_handle_kind) async'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.11.
File: libgomp.info, Node: acc_wait_async, Next: acc_init, Prev: acc_wait_all_async, Up: OpenACC Runtime Library Routines
5.11 'acc_wait_async' - Wait for completion of asynchronous operations.
=======================================================================
_Description_
This function enqueues a wait operation on queue ASYNC for any and
all asynchronous operations enqueued on queue ARG.
_C/C++_:
_Prototype_: 'acc_wait_async(int arg, int async);'
_Fortran_:
_Interface_: 'subroutine acc_wait_async(arg, async)'
'integer(acc_handle_kind) arg, async'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.9.
File: libgomp.info, Node: acc_init, Next: acc_shutdown, Prev: acc_wait_async, Up: OpenACC Runtime Library Routines
5.12 'acc_init' - Initialize runtime for a specific device type.
================================================================
_Description_
This function initializes the runtime for the device type specified
in DEVICETYPE.
_C/C++_:
_Prototype_: 'acc_init(acc_device_t devicetype);'
_Fortran_:
_Interface_: 'subroutine acc_init(devicetype)'
'integer(acc_device_kind) devicetype'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.12.
File: libgomp.info, Node: acc_shutdown, Next: acc_on_device, Prev: acc_init, Up: OpenACC Runtime Library Routines
5.13 'acc_shutdown' - Shuts down the runtime for a specific device type.
========================================================================
_Description_
This function shuts down the runtime for the device type specified
in DEVICETYPE.
_C/C++_:
_Prototype_: 'acc_shutdown(acc_device_t devicetype);'
_Fortran_:
_Interface_: 'subroutine acc_shutdown(devicetype)'
'integer(acc_device_kind) devicetype'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.13.
File: libgomp.info, Node: acc_on_device, Next: acc_malloc, Prev: acc_shutdown, Up: OpenACC Runtime Library Routines
5.14 'acc_on_device' - Whether executing on a particular device
===============================================================
_Description_:
This function returns whether the program is executing on a
particular device specified in DEVICETYPE. In C/C++ a non-zero
value is returned to indicate the device is execiting on the
specified device type. In Fortran, 'true' will be returned. If
the program is not executing on the specified device type C/C++
will return a zero, while Fortran will return 'false'.
_C/C++_:
_Prototype_: 'acc_on_device(acc_device_t devicetype);'
_Fortran_:
_Interface_: 'function acc_on_device(devicetype)'
'integer(acc_device_kind) devicetype'
'logical acc_on_device'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.14.
File: libgomp.info, Node: acc_malloc, Next: acc_free, Prev: acc_on_device, Up: OpenACC Runtime Library Routines
5.15 'acc_malloc' - Allocate device memory.
===========================================
_Description_
This function allocates LEN bytes of device memory. It returns the
device address of the allocated memory.
_C/C++_:
_Prototype_: 'd_void* acc_malloc(size_t len);'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.15.
File: libgomp.info, Node: acc_free, Next: acc_copyin, Prev: acc_malloc, Up: OpenACC Runtime Library Routines
5.16 'acc_free' - Free device memory.
=====================================
_Description_
Free previously allocated device memory at the device address 'a'.
_C/C++_:
_Prototype_: 'acc_free(d_void *a);'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.16.
File: libgomp.info, Node: acc_copyin, Next: acc_present_or_copyin, Prev: acc_free, Up: OpenACC Runtime Library Routines
5.17 'acc_copyin' - Allocate device memory and copy host memory to it.
======================================================================
_Description_
In C/C++, this function allocates LEN bytes of device memory and
maps it to the specified host address in A. The device address of
the newly allocated device memory is returned.
In Fortran, two (2) forms are supported. In the first form, A
specifies a contiguous array section. The second form A specifies
a variable or array element and LEN specifies the length in bytes.
_C/C++_:
_Prototype_: 'void *acc_copyin(h_void *a, size_t len);'
_Fortran_:
_Interface_: 'subroutine acc_copyin(a)'
'type, dimension(:[,:]...) :: a'
_Interface_: 'subroutine acc_copyin(a, len)'
'type, dimension(:[,:]...) :: a'
'integer len'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.17.
File: libgomp.info, Node: acc_present_or_copyin, Next: acc_create, Prev: acc_copyin, Up: OpenACC Runtime Library Routines
5.18 'acc_present_or_copyin' - If the data is not present on the device, allocate device memory and copy from host memory.
==========================================================================================================================
_Description_
This function tests if the host data specifed by A and of length
LEN is present or not. If it is not present, then device memory
will be allocated and the host memory copied. The device address
of the newly allocated device memory is returned.
In Fortran, two (2) forms are supported. In the first form, A
specifies a contiguous array section. The second form A specifies
a variable or array element and LEN specifies the length in bytes.
_C/C++_:
_Prototype_: 'void *acc_present_or_copyin(h_void *a, size_t len);'
_Prototype_: 'void *acc_pcopyin(h_void *a, size_t len);'
_Fortran_:
_Interface_: 'subroutine acc_present_or_copyin(a)'
'type, dimension(:[,:]...) :: a'
_Interface_: 'subroutine acc_present_or_copyin(a, len)'
'type, dimension(:[,:]...) :: a'
'integer len'
_Interface_: 'subroutine acc_pcopyin(a)'
'type, dimension(:[,:]...) :: a'
_Interface_: 'subroutine acc_pcopyin(a, len)'
'type, dimension(:[,:]...) :: a'
'integer len'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.18.
File: libgomp.info, Node: acc_create, Next: acc_present_or_create, Prev: acc_present_or_copyin, Up: OpenACC Runtime Library Routines
5.19 'acc_create' - Allocate device memory and map it to host memory.
=====================================================================
_Description_
This function allocates device memory and maps it to host memory
specified by the host address A with a length of LEN bytes. In
C/C++, the function returns the device address of the allocated
device memory.
In Fortran, two (2) forms are supported. In the first form, A
specifies a contiguous array section. The second form A specifies
a variable or array element and LEN specifies the length in bytes.
_C/C++_:
_Prototype_: 'void *acc_create(h_void *a, size_t len);'
_Fortran_:
_Interface_: 'subroutine acc_create(a)'
'type, dimension(:[,:]...) :: a'
_Interface_: 'subroutine acc_create(a, len)'
'type, dimension(:[,:]...) :: a'
'integer len'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.19.
File: libgomp.info, Node: acc_present_or_create, Next: acc_copyout, Prev: acc_create, Up: OpenACC Runtime Library Routines
5.20 'acc_present_or_create' - If the data is not present on the device, allocate device memory and map it to host memory.
==========================================================================================================================
_Description_
This function tests if the host data specifed by A and of length
LEN is present or not. If it is not present, then device memory
will be allocated and mapped to host memory. In C/C++, the device
address of the newly allocated device memory is returned.
In Fortran, two (2) forms are supported. In the first form, A
specifies a contiguous array section. The second form A specifies
a variable or array element and LEN specifies the length in bytes.
_C/C++_:
_Prototype_: 'void *acc_present_or_create(h_void *a, size_t len)'
_Prototype_: 'void *acc_pcreate(h_void *a, size_t len)'
_Fortran_:
_Interface_: 'subroutine acc_present_or_create(a)'
'type, dimension(:[,:]...) :: a'
_Interface_: 'subroutine acc_present_or_create(a, len)'
'type, dimension(:[,:]...) :: a'
'integer len'
_Interface_: 'subroutine acc_pcreate(a)'
'type, dimension(:[,:]...) :: a'
_Interface_: 'subroutine acc_pcreate(a, len)'
'type, dimension(:[,:]...) :: a'
'integer len'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.20.
File: libgomp.info, Node: acc_copyout, Next: acc_delete, Prev: acc_present_or_create, Up: OpenACC Runtime Library Routines
5.21 'acc_copyout' - Copy device memory to host memory.
=======================================================
_Description_
This function copies mapped device memory to host memory which is
specified by host address A for a length LEN bytes in C/C++.
In Fortran, two (2) forms are supported. In the first form, A
specifies a contiguous array section. The second form A specifies
a variable or array element and LEN specifies the length in bytes.
_C/C++_:
_Prototype_: 'acc_copyout(h_void *a, size_t len);'
_Fortran_:
_Interface_: 'subroutine acc_copyout(a)'
'type, dimension(:[,:]...) :: a'
_Interface_: 'subroutine acc_copyout(a, len)'
'type, dimension(:[,:]...) :: a'
'integer len'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.21.
File: libgomp.info, Node: acc_delete, Next: acc_update_device, Prev: acc_copyout, Up: OpenACC Runtime Library Routines
5.22 'acc_delete' - Free device memory.
=======================================
_Description_
This function frees previously allocated device memory specified by
the device address A and the length of LEN bytes.
In Fortran, two (2) forms are supported. In the first form, A
specifies a contiguous array section. The second form A specifies
a variable or array element and LEN specifies the length in bytes.
_C/C++_:
_Prototype_: 'acc_delete(h_void *a, size_t len);'
_Fortran_:
_Interface_: 'subroutine acc_delete(a)'
'type, dimension(:[,:]...) :: a'
_Interface_: 'subroutine acc_delete(a, len)'
'type, dimension(:[,:]...) :: a'
'integer len'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.22.
File: libgomp.info, Node: acc_update_device, Next: acc_update_self, Prev: acc_delete, Up: OpenACC Runtime Library Routines
5.23 'acc_update_device' - Update device memory from mapped host memory.
========================================================================
_Description_
This function updates the device copy from the previously mapped
host memory. The host memory is specified with the host address A
and a length of LEN bytes.
In Fortran, two (2) forms are supported. In the first form, A
specifies a contiguous array section. The second form A specifies
a variable or array element and LEN specifies the length in bytes.
_C/C++_:
_Prototype_: 'acc_update_device(h_void *a, size_t len);'
_Fortran_:
_Interface_: 'subroutine acc_update_device(a)'
'type, dimension(:[,:]...) :: a'
_Interface_: 'subroutine acc_update_device(a, len)'
'type, dimension(:[,:]...) :: a'
'integer len'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.23.
File: libgomp.info, Node: acc_update_self, Next: acc_map_data, Prev: acc_update_device, Up: OpenACC Runtime Library Routines
5.24 'acc_update_self' - Update host memory from mapped device memory.
======================================================================
_Description_
This function updates the host copy from the previously mapped
device memory. The host memory is specified with the host address
A and a length of LEN bytes.
In Fortran, two (2) forms are supported. In the first form, A
specifies a contiguous array section. The second form A specifies
a variable or array element and LEN specifies the length in bytes.
_C/C++_:
_Prototype_: 'acc_update_self(h_void *a, size_t len);'
_Fortran_:
_Interface_: 'subroutine acc_update_self(a)'
'type, dimension(:[,:]...) :: a'
_Interface_: 'subroutine acc_update_self(a, len)'
'type, dimension(:[,:]...) :: a'
'integer len'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.24.
File: libgomp.info, Node: acc_map_data, Next: acc_unmap_data, Prev: acc_update_self, Up: OpenACC Runtime Library Routines
5.25 'acc_map_data' - Map previously allocated device memory to host memory.
============================================================================
_Description_
This function maps previously allocated device and host memory.
The device memory is specified with the device address D. The host
memory is specified with the host address H and a length of LEN.
_C/C++_:
_Prototype_: 'acc_map_data(h_void *h, d_void *d, size_t len);'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.25.
File: libgomp.info, Node: acc_unmap_data, Next: acc_deviceptr, Prev: acc_map_data, Up: OpenACC Runtime Library Routines
5.26 'acc_unmap_data' - Unmap device memory from host memory.
=============================================================
_Description_
This function unmaps previously mapped device and host memory. The
latter specified by H.
_C/C++_:
_Prototype_: 'acc_unmap_data(h_void *h);'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.26.
File: libgomp.info, Node: acc_deviceptr, Next: acc_hostptr, Prev: acc_unmap_data, Up: OpenACC Runtime Library Routines
5.27 'acc_deviceptr' - Get device pointer associated with specific host address.
================================================================================
_Description_
This function returns the device address that has been mapped to
the host address specified by H.
_C/C++_:
_Prototype_: 'void *acc_deviceptr(h_void *h);'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.27.
File: libgomp.info, Node: acc_hostptr, Next: acc_is_present, Prev: acc_deviceptr, Up: OpenACC Runtime Library Routines
5.28 'acc_hostptr' - Get host pointer associated with specific device address.
==============================================================================
_Description_
This function returns the host address that has been mapped to the
device address specified by D.
_C/C++_:
_Prototype_: 'void *acc_hostptr(d_void *d);'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.28.
File: libgomp.info, Node: acc_is_present, Next: acc_memcpy_to_device, Prev: acc_hostptr, Up: OpenACC Runtime Library Routines
5.29 'acc_is_present' - Indicate whether host variable / array is present on device.
====================================================================================
_Description_
This function indicates whether the specified host address in A and
a length of LEN bytes is present on the device. In C/C++, a
non-zero value is returned to indicate the presence of the mapped
memory on the device. A zero is returned to indicate the memory is
not mapped on the device.
In Fortran, two (2) forms are supported. In the first form, A
specifies a contiguous array section. The second form A specifies
a variable or array element and LEN specifies the length in bytes.
If the host memory is mapped to device memory, then a 'true' is
returned. Otherwise, a 'false' is return to indicate the mapped
memory is not present.
_C/C++_:
_Prototype_: 'int acc_is_present(h_void *a, size_t len);'
_Fortran_:
_Interface_: 'function acc_is_present(a)'
'type, dimension(:[,:]...) :: a'
'logical acc_is_present'
_Interface_: 'function acc_is_present(a, len)'
'type, dimension(:[,:]...) :: a'
'integer len'
'logical acc_is_present'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.29.
File: libgomp.info, Node: acc_memcpy_to_device, Next: acc_memcpy_from_device, Prev: acc_is_present, Up: OpenACC Runtime Library Routines
5.30 'acc_memcpy_to_device' - Copy host memory to device memory.
================================================================
_Description_
This function copies host memory specified by host address of SRC
to device memory specified by the device address DEST for a length
of BYTES bytes.
_C/C++_:
_Prototype_: 'acc_memcpy_to_device(d_void *dest, h_void *src, size_t
bytes);'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.30.
File: libgomp.info, Node: acc_memcpy_from_device, Next: acc_get_current_cuda_device, Prev: acc_memcpy_to_device, Up: OpenACC Runtime Library Routines
5.31 'acc_memcpy_from_device' - Copy device memory to host memory.
==================================================================
_Description_
This function copies host memory specified by host address of SRC
from device memory specified by the device address DEST for a
length of BYTES bytes.
_C/C++_:
_Prototype_: 'acc_memcpy_from_device(d_void *dest, h_void *src,
size_t bytes);'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
3.2.31.
File: libgomp.info, Node: acc_get_current_cuda_device, Next: acc_get_current_cuda_context, Prev: acc_memcpy_from_device, Up: OpenACC Runtime Library Routines
5.32 'acc_get_current_cuda_device' - Get CUDA device handle.
============================================================
_Description_
This function returns the CUDA device handle. This handle is the
same as used by the CUDA Runtime or Driver API's.
_C/C++_:
_Prototype_: 'void *acc_get_current_cuda_device(void);'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
A.2.1.1.
File: libgomp.info, Node: acc_get_current_cuda_context, Next: acc_get_cuda_stream, Prev: acc_get_current_cuda_device, Up: OpenACC Runtime Library Routines
5.33 'acc_get_current_cuda_context' - Get CUDA context handle.
==============================================================
_Description_
This function returns the CUDA context handle. This handle is the
same as used by the CUDA Runtime or Driver API's.
_C/C++_:
_Prototype_: 'acc_get_current_cuda_context(void);'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
A.2.1.2.
File: libgomp.info, Node: acc_get_cuda_stream, Next: acc_set_cuda_stream, Prev: acc_get_current_cuda_context, Up: OpenACC Runtime Library Routines
5.34 'acc_get_cuda_stream' - Get CUDA stream handle.
====================================================
_Description_
This function returns the CUDA stream handle. This handle is the
same as used by the CUDA Runtime or Driver API's.
_C/C++_:
_Prototype_: 'acc_get_cuda_stream(void);'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
A.2.1.3.
File: libgomp.info, Node: acc_set_cuda_stream, Prev: acc_get_cuda_stream, Up: OpenACC Runtime Library Routines
5.35 'acc_set_cuda_stream' - Set CUDA stream handle.
====================================================
_Description_
This function associates the stream handle specified by STREAM with
the asynchronous value specified by ASYNC.
_C/C++_:
_Prototype_: 'acc_set_cuda_stream(int async void *stream);'
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section
A.2.1.4.
File: libgomp.info, Node: OpenACC Environment Variables, Next: CUDA Streams Usage, Prev: OpenACC Runtime Library Routines, Up: Top
6 OpenACC Environment Variables
*******************************
The variables 'ACC_DEVICE_TYPE' and 'ACC_DEVICE_NUM' are defined by
section 4 of the OpenACC specification in version 2.0. The variable
'GCC_ACC_NOTIFY' is used for diagnostic purposes.
* Menu:
* ACC_DEVICE_TYPE::
* ACC_DEVICE_NUM::
* GCC_ACC_NOTIFY::
File: libgomp.info, Node: ACC_DEVICE_TYPE, Next: ACC_DEVICE_NUM, Up: OpenACC Environment Variables
6.1 'ACC_DEVICE_TYPE'
=====================
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section 4.1.
File: libgomp.info, Node: ACC_DEVICE_NUM, Next: GCC_ACC_NOTIFY, Prev: ACC_DEVICE_TYPE, Up: OpenACC Environment Variables
6.2 'ACC_DEVICE_NUM'
====================
_Reference_:
OpenACC specification v2.0 (https://www.openacc.org), section 4.2.
File: libgomp.info, Node: GCC_ACC_NOTIFY, Prev: ACC_DEVICE_NUM, Up: OpenACC Environment Variables
6.3 'GCC_ACC_NOTIFY'
====================
_Description_:
Print debug information pertaining to the accelerator.
File: libgomp.info, Node: CUDA Streams Usage, Next: OpenACC Library Interoperability, Prev: OpenACC Environment Variables, Up: Top
7 CUDA Streams Usage
********************
This applies to the 'nvptx' plugin only.
The library provides elements that perform asynchronous movement of
data and asynchronous operation of computing constructs. This
asynchronous functionality is implemented by making use of CUDA
streams(1).
The primary means by that the asychronous functionality is accessed
is through the use of those OpenACC directives which make use of the
'async' and 'wait' clauses. When the 'async' clause is first used with
a directive, it creates a CUDA stream. If an 'async-argument' is used
with the 'async' clause, then the stream is associated with the
specified 'async-argument'.
Following the creation of an association between a CUDA stream and
the 'async-argument' of an 'async' clause, both the 'wait' clause and
the 'wait' directive can be used. When either the clause or directive
is used after stream creation, it creates a rendezvous point whereby
execution waits until all operations associated with the
'async-argument', that is, stream, have completed.
Normally, the management of the streams that are created as a result
of using the 'async' clause, is done without any intervention by the
caller. This implies the association between the 'async-argument' and
the CUDA stream will be maintained for the lifetime of the program.
However, this association can be changed through the use of the library
function 'acc_set_cuda_stream'. When the function 'acc_set_cuda_stream'
is called, the CUDA stream that was originally associated with the
'async' clause will be destroyed. Caution should be taken when changing
the association as subsequent references to the 'async-argument' refer
to a different CUDA stream.
---------- Footnotes ----------
(1) See "Stream Management" in "CUDA Driver API", TRM-06703-001,
Version 5.5, for additional information
File: libgomp.info, Node: OpenACC Library Interoperability, Next: The libgomp ABI, Prev: CUDA Streams Usage, Up: Top
8 OpenACC Library Interoperability
**********************************
8.1 Introduction
================
The OpenACC library uses the CUDA Driver API, and may interact with
programs that use the Runtime library directly, or another library based
on the Runtime library, e.g., CUBLAS(1). This chapter describes the use
cases and what changes are required in order to use both the OpenACC
library and the CUBLAS and Runtime libraries within a program.
8.2 First invocation: NVIDIA CUBLAS library API
===============================================
In this first use case (see below), a function in the CUBLAS library is
called prior to any of the functions in the OpenACC library. More
specifically, the function 'cublasCreate()'.
When invoked, the function initializes the library and allocates the
hardware resources on the host and the device on behalf of the caller.
Once the initialization and allocation has completed, a handle is
returned to the caller. The OpenACC library also requires
initialization and allocation of hardware resources. Since the CUBLAS
library has already allocated the hardware resources for the device, all
that is left to do is to initialize the OpenACC library and acquire the
hardware resources on the host.
Prior to calling the OpenACC function that initializes the library
and allocate the host hardware resources, you need to acquire the device
number that was allocated during the call to 'cublasCreate()'. The
invoking of the runtime library function 'cudaGetDevice()' accomplishes
this. Once acquired, the device number is passed along with the device
type as parameters to the OpenACC library function
'acc_set_device_num()'.
Once the call to 'acc_set_device_num()' has completed, the OpenACC
library uses the context that was created during the call to
'cublasCreate()'. In other words, both libraries will be sharing the
same context.
/* Create the handle */
s = cublasCreate(&h);
if (s != CUBLAS_STATUS_SUCCESS)
{
fprintf(stderr, "cublasCreate failed %d\n", s);
exit(EXIT_FAILURE);
}
/* Get the device number */
e = cudaGetDevice(&dev);
if (e != cudaSuccess)
{
fprintf(stderr, "cudaGetDevice failed %d\n", e);
exit(EXIT_FAILURE);
}
/* Initialize OpenACC library and use device 'dev' */
acc_set_device_num(dev, acc_device_nvidia);
Use Case 1
8.3 First invocation: OpenACC library API
=========================================
In this second use case (see below), a function in the OpenACC library
is called prior to any of the functions in the CUBLAS library. More
specificially, the function 'acc_set_device_num()'.
In the use case presented here, the function 'acc_set_device_num()'
is used to both initialize the OpenACC library and allocate the hardware
resources on the host and the device. In the call to the function, the
call parameters specify which device to use and what device type to use,
i.e., 'acc_device_nvidia'. It should be noted that this is but one
method to initialize the OpenACC library and allocate the appropriate
hardware resources. Other methods are available through the use of
environment variables and these will be discussed in the next section.
Once the call to 'acc_set_device_num()' has completed, other OpenACC
functions can be called as seen with multiple calls being made to
'acc_copyin()'. In addition, calls can be made to functions in the
CUBLAS library. In the use case a call to 'cublasCreate()' is made
subsequent to the calls to 'acc_copyin()'. As seen in the previous use
case, a call to 'cublasCreate()' initializes the CUBLAS library and
allocates the hardware resources on the host and the device. However,
since the device has already been allocated, 'cublasCreate()' will only
initialize the CUBLAS library and allocate the appropriate hardware
resources on the host. The context that was created as part of the
OpenACC initialization is shared with the CUBLAS library, similarly to
the first use case.
dev = 0;
acc_set_device_num(dev, acc_device_nvidia);
/* Copy the first set to the device */
d_X = acc_copyin(&h_X[0], N * sizeof (float));
if (d_X == NULL)
{
fprintf(stderr, "copyin error h_X\n");
exit(EXIT_FAILURE);
}
/* Copy the second set to the device */
d_Y = acc_copyin(&h_Y1[0], N * sizeof (float));
if (d_Y == NULL)
{
fprintf(stderr, "copyin error h_Y1\n");
exit(EXIT_FAILURE);
}
/* Create the handle */
s = cublasCreate(&h);
if (s != CUBLAS_STATUS_SUCCESS)
{
fprintf(stderr, "cublasCreate failed %d\n", s);
exit(EXIT_FAILURE);
}
/* Perform saxpy using CUBLAS library function */
s = cublasSaxpy(h, N, &alpha, d_X, 1, d_Y, 1);
if (s != CUBLAS_STATUS_SUCCESS)
{
fprintf(stderr, "cublasSaxpy failed %d\n", s);
exit(EXIT_FAILURE);
}
/* Copy the results from the device */
acc_memcpy_from_device(&h_Y1[0], d_Y, N * sizeof (float));
Use Case 2
8.4 OpenACC library and environment variables
=============================================
There are two environment variables associated with the OpenACC library
that may be used to control the device type and device number:
'ACC_DEVICE_TYPE' and 'ACC_DEVICE_NUM', respecively. These two
environement variables can be used as an alternative to calling
'acc_set_device_num()'. As seen in the second use case, the device type
and device number were specified using 'acc_set_device_num()'. If
however, the aforementioned environment variables were set, then the
call to 'acc_set_device_num()' would not be required.
The use of the environment variables is only relevant when an OpenACC
function is called prior to a call to 'cudaCreate()'. If 'cudaCreate()'
is called prior to a call to an OpenACC function, then you must call
'acc_set_device_num()'(2)
---------- Footnotes ----------
(1) See section 2.26, "Interactions with the CUDA Driver API" in
"CUDA Runtime API", Version 5.5, and section 2.27, "VDPAU
Interoperability", in "CUDA Driver API", TRM-06703-001, Version 5.5, for
additional information on library interoperability.
(2) More complete information about 'ACC_DEVICE_TYPE' and
'ACC_DEVICE_NUM' can be found in sections 4.1 and 4.2 of the OpenACC
(https://www.openacc.org) Application Programming Interfaceâ€, Version
2.0.
File: libgomp.info, Node: The libgomp ABI, Next: Reporting Bugs, Prev: OpenACC Library Interoperability, Up: Top
9 The libgomp ABI
*****************
The following sections present notes on the external ABI as presented by
libgomp. Only maintainers should need them.
* Menu:
* Implementing MASTER construct::
* Implementing CRITICAL construct::
* Implementing ATOMIC construct::
* Implementing FLUSH construct::
* Implementing BARRIER construct::
* Implementing THREADPRIVATE construct::
* Implementing PRIVATE clause::
* Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses::
* Implementing REDUCTION clause::
* Implementing PARALLEL construct::
* Implementing FOR construct::
* Implementing ORDERED construct::
* Implementing SECTIONS construct::
* Implementing SINGLE construct::
* Implementing OpenACC's PARALLEL construct::
File: libgomp.info, Node: Implementing MASTER construct, Next: Implementing CRITICAL construct, Up: The libgomp ABI
9.1 Implementing MASTER construct
=================================
if (omp_get_thread_num () == 0)
block
Alternately, we generate two copies of the parallel subfunction and
only include this in the version run by the master thread. Surely this
is not worthwhile though...
File: libgomp.info, Node: Implementing CRITICAL construct, Next: Implementing ATOMIC construct, Prev: Implementing MASTER construct, Up: The libgomp ABI
9.2 Implementing CRITICAL construct
===================================
Without a specified name,
void GOMP_critical_start (void);
void GOMP_critical_end (void);
so that we don't get COPY relocations from libgomp to the main
application.
With a specified name, use omp_set_lock and omp_unset_lock with name
being transformed into a variable declared like
omp_lock_t gomp_critical_user_<name> __attribute__((common))
Ideally the ABI would specify that all zero is a valid unlocked
state, and so we wouldn't need to initialize this at startup.
File: libgomp.info, Node: Implementing ATOMIC construct, Next: Implementing FLUSH construct, Prev: Implementing CRITICAL construct, Up: The libgomp ABI
9.3 Implementing ATOMIC construct
=================================
The target should implement the '__sync' builtins.
Failing that we could add
void GOMP_atomic_enter (void)
void GOMP_atomic_exit (void)
which reuses the regular lock code, but with yet another lock object
private to the library.
File: libgomp.info, Node: Implementing FLUSH construct, Next: Implementing BARRIER construct, Prev: Implementing ATOMIC construct, Up: The libgomp ABI
9.4 Implementing FLUSH construct
================================
Expands to the '__sync_synchronize' builtin.
File: libgomp.info, Node: Implementing BARRIER construct, Next: Implementing THREADPRIVATE construct, Prev: Implementing FLUSH construct, Up: The libgomp ABI
9.5 Implementing BARRIER construct
==================================
void GOMP_barrier (void)
File: libgomp.info, Node: Implementing THREADPRIVATE construct, Next: Implementing PRIVATE clause, Prev: Implementing BARRIER construct, Up: The libgomp ABI
9.6 Implementing THREADPRIVATE construct
========================================
In _most_ cases we can map this directly to '__thread'. Except that OMP
allows constructors for C++ objects. We can either refuse to support
this (how often is it used?) or we can implement something akin to
.ctors.
Even more ideally, this ctor feature is handled by extensions to the
main pthreads library. Failing that, we can have a set of entry points
to register ctor functions to be called.
File: libgomp.info, Node: Implementing PRIVATE clause, Next: Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses, Prev: Implementing THREADPRIVATE construct, Up: The libgomp ABI
9.7 Implementing PRIVATE clause
===============================
In association with a PARALLEL, or within the lexical extent of a
PARALLEL block, the variable becomes a local variable in the parallel
subfunction.
In association with FOR or SECTIONS blocks, create a new automatic
variable within the current function. This preserves the semantic of
new variable creation.
File: libgomp.info, Node: Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses, Next: Implementing REDUCTION clause, Prev: Implementing PRIVATE clause, Up: The libgomp ABI
9.8 Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses
========================================================================
This seems simple enough for PARALLEL blocks. Create a private struct
for communicating between the parent and subfunction. In the parent,
copy in values for scalar and "small" structs; copy in addresses for
others TREE_ADDRESSABLE types. In the subfunction, copy the value into
the local variable.
It is not clear what to do with bare FOR or SECTION blocks. The only
thing I can figure is that we do something like:
#pragma omp for firstprivate(x) lastprivate(y)
for (int i = 0; i < n; ++i)
body;
which becomes
{
int x = x, y;
// for stuff
if (i == n)
y = y;
}
where the "x=x" and "y=y" assignments actually have different uids
for the two variables, i.e. not something you could write directly in
C. Presumably this only makes sense if the "outer" x and y are global
variables.
COPYPRIVATE would work the same way, except the structure broadcast
would have to happen via SINGLE machinery instead.
File: libgomp.info, Node: Implementing REDUCTION clause, Next: Implementing PARALLEL construct, Prev: Implementing FIRSTPRIVATE LASTPRIVATE COPYIN and COPYPRIVATE clauses, Up: The libgomp ABI
9.9 Implementing REDUCTION clause
=================================
The private struct mentioned in the previous section should have a
pointer to an array of the type of the variable, indexed by the thread's
TEAM_ID. The thread stores its final value into the array, and after
the barrier, the master thread iterates over the array to collect the
values.
File: libgomp.info, Node: Implementing PARALLEL construct, Next: Implementing FOR construct, Prev: Implementing REDUCTION clause, Up: The libgomp ABI
9.10 Implementing PARALLEL construct
====================================
#pragma omp parallel
{
body;
}
becomes
void subfunction (void *data)
{
use data;
body;
}
setup data;
GOMP_parallel_start (subfunction, &data, num_threads);
subfunction (&data);
GOMP_parallel_end ();
void GOMP_parallel_start (void (*fn)(void *), void *data, unsigned num_threads)
The FN argument is the subfunction to be run in parallel.
The DATA argument is a pointer to a structure used to communicate
data in and out of the subfunction, as discussed above with respect to
FIRSTPRIVATE et al.
The NUM_THREADS argument is 1 if an IF clause is present and false,
or the value of the NUM_THREADS clause, if present, or 0.
The function needs to create the appropriate number of threads and/or
launch them from the dock. It needs to create the team structure and
assign team ids.
void GOMP_parallel_end (void)
Tears down the team and returns us to the previous
'omp_in_parallel()' state.
File: libgomp.info, Node: Implementing FOR construct, Next: Implementing ORDERED construct, Prev: Implementing PARALLEL construct, Up: The libgomp ABI
9.11 Implementing FOR construct
===============================
#pragma omp parallel for
for (i = lb; i <= ub; i++)
body;
becomes
void subfunction (void *data)
{
long _s0, _e0;
while (GOMP_loop_static_next (&_s0, &_e0))
{
long _e1 = _e0, i;
for (i = _s0; i < _e1; i++)
body;
}
GOMP_loop_end_nowait ();
}
GOMP_parallel_loop_static (subfunction, NULL, 0, lb, ub+1, 1, 0);
subfunction (NULL);
GOMP_parallel_end ();
#pragma omp for schedule(runtime)
for (i = 0; i < n; i++)
body;
becomes
{
long i, _s0, _e0;
if (GOMP_loop_runtime_start (0, n, 1, &_s0, &_e0))
do {
long _e1 = _e0;
for (i = _s0, i < _e0; i++)
body;
} while (GOMP_loop_runtime_next (&_s0, _&e0));
GOMP_loop_end ();
}
Note that while it looks like there is trickiness to propagating a
non-constant STEP, there isn't really. We're explicitly allowed to
evaluate it as many times as we want, and any variables involved should
automatically be handled as PRIVATE or SHARED like any other variables.
So the expression should remain evaluable in the subfunction. We can
also pull it into a local variable if we like, but since its supposed to
remain unchanged, we can also not if we like.
If we have SCHEDULE(STATIC), and no ORDERED, then we ought to be able
to get away with no work-sharing context at all, since we can simply
perform the arithmetic directly in each thread to divide up the
iterations. Which would mean that we wouldn't need to call any of these
routines.
There are separate routines for handling loops with an ORDERED
clause. Bookkeeping for that is non-trivial...
File: libgomp.info, Node: Implementing ORDERED construct, Next: Implementing SECTIONS construct, Prev: Implementing FOR construct, Up: The libgomp ABI
9.12 Implementing ORDERED construct
===================================
void GOMP_ordered_start (void)
void GOMP_ordered_end (void)
File: libgomp.info, Node: Implementing SECTIONS construct, Next: Implementing SINGLE construct, Prev: Implementing ORDERED construct, Up: The libgomp ABI
9.13 Implementing SECTIONS construct
====================================
A block as
#pragma omp sections
{
#pragma omp section
stmt1;
#pragma omp section
stmt2;
#pragma omp section
stmt3;
}
becomes
for (i = GOMP_sections_start (3); i != 0; i = GOMP_sections_next ())
switch (i)
{
case 1:
stmt1;
break;
case 2:
stmt2;
break;
case 3:
stmt3;
break;
}
GOMP_barrier ();
File: libgomp.info, Node: Implementing SINGLE construct, Next: Implementing OpenACC's PARALLEL construct, Prev: Implementing SECTIONS construct, Up: The libgomp ABI
9.14 Implementing SINGLE construct
==================================
A block like
#pragma omp single
{
body;
}
becomes
if (GOMP_single_start ())
body;
GOMP_barrier ();
while
#pragma omp single copyprivate(x)
body;
becomes
datap = GOMP_single_copy_start ();
if (datap == NULL)
{
body;
data.x = x;
GOMP_single_copy_end (&data);
}
else
x = datap->x;
GOMP_barrier ();
File: libgomp.info, Node: Implementing OpenACC's PARALLEL construct, Prev: Implementing SINGLE construct, Up: The libgomp ABI
9.15 Implementing OpenACC's PARALLEL construct
==============================================
void GOACC_parallel ()
File: libgomp.info, Node: Reporting Bugs, Next: Copying, Prev: The libgomp ABI, Up: Top
10 Reporting Bugs
*****************
Bugs in the GNU Offloading and Multi Processing Runtime Library should
be reported via Bugzilla (http://gcc.gnu.org/bugzilla/). Please add
"openacc", or "openmp", or both to the keywords field in the bug report,
as appropriate.
File: libgomp.info, Node: Copying, Next: GNU Free Documentation License, Prev: Reporting Bugs, Up: Top
GNU General Public License
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Version 3, 29 June 2007
Copyright (C) 2007 Free Software Foundation, Inc. <http://fsf.org/>;
Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.
Preamble
========
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TERMS AND CONDITIONS
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Notwithstanding any other provision of this License, you have
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THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
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IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES
AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR
DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR
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BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
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If the disclaimer of warranty and limitation of liability provided
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END OF TERMS AND CONDITIONS
===========================
How to Apply These Terms to Your New Programs
=============================================
If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.
To do so, attach the following notices to the program. It is safest
to attach them to the start of each source file to most effectively
state the exclusion of warranty; and each file should have at least the
"copyright" line and a pointer to where the full notice is found.
ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
Copyright (C) YEAR NAME OF AUTHOR
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>;.
Also add information on how to contact you by electronic and paper
mail.
If the program does terminal interaction, make it output a short
notice like this when it starts in an interactive mode:
PROGRAM Copyright (C) YEAR NAME OF AUTHOR
This program comes with ABSOLUTELY NO WARRANTY; for details type 'show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type 'show c' for details.
The hypothetical commands 'show w' and 'show c' should show the
appropriate parts of the General Public License. Of course, your
program's commands might be different; for a GUI interface, you would
use an "about box".
You should also get your employer (if you work as a programmer) or
school, if any, to sign a "copyright disclaimer" for the program, if
necessary. For more information on this, and how to apply and follow
the GNU GPL, see <http://www.gnu.org/licenses/>;.
The GNU General Public License does not permit incorporating your
program into proprietary programs. If your program is a subroutine
library, you may consider it more useful to permit linking proprietary
applications with the library. If this is what you want to do, use the
GNU Lesser General Public License instead of this License. But first,
please read <http://www.gnu.org/philosophy/why-not-lgpl.html>;.
File: libgomp.info, Node: GNU Free Documentation License, Next: Funding, Prev: Copying, Up: Top
GNU Free Documentation License
******************************
Version 1.3, 3 November 2008
Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
<http://fsf.org/>;
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or
noncommercially. Secondarily, this License preserves for the
author and publisher a way to get credit for their work, while not
being considered responsible for modifications made by others.
This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.
It complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for
free software, because free software needs free documentation: a
free program should come with manuals providing the same freedoms
that the software does. But this License is not limited to
software manuals; it can be used for any textual work, regardless
of subject matter or whether it is published as a printed book. We
recommend this License principally for works whose purpose is
instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium,
that contains a notice placed by the copyright holder saying it can
be distributed under the terms of this License. Such a notice
grants a world-wide, royalty-free license, unlimited in duration,
to use that work under the conditions stated herein. The
"Document", below, refers to any such manual or work. Any member
of the public is a licensee, and is addressed as "you". You accept
the license if you copy, modify or distribute the work in a way
requiring permission under copyright law.
A "Modified Version" of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.
A "Secondary Section" is a named appendix or a front-matter section
of the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document's overall
subject (or to related matters) and contains nothing that could
fall directly within that overall subject. (Thus, if the Document
is in part a textbook of mathematics, a Secondary Section may not
explain any mathematics.) The relationship could be a matter of
historical connection with the subject or with related matters, or
of legal, commercial, philosophical, ethical or political position
regarding them.
The "Invariant Sections" are certain Secondary Sections whose
titles are designated, as being those of Invariant Sections, in the
notice that says that the Document is released under this License.
If a section does not fit the above definition of Secondary then it
is not allowed to be designated as Invariant. The Document may
contain zero Invariant Sections. If the Document does not identify
any Invariant Sections then there are none.
The "Cover Texts" are certain short passages of text that are
listed, as Front-Cover Texts or Back-Cover Texts, in the notice
that says that the Document is released under this License. A
Front-Cover Text may be at most 5 words, and a Back-Cover Text may
be at most 25 words.
A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
general public, that is suitable for revising the document
straightforwardly with generic text editors or (for images composed
of pixels) generic paint programs or (for drawings) some widely
available drawing editor, and that is suitable for input to text
formatters or for automatic translation to a variety of formats
suitable for input to text formatters. A copy made in an otherwise
Transparent file format whose markup, or absence of markup, has
been arranged to thwart or discourage subsequent modification by
readers is not Transparent. An image format is not Transparent if
used for any substantial amount of text. A copy that is not
"Transparent" is called "Opaque".
Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, LaTeX input format,
SGML or XML using a publicly available DTD, and standard-conforming
simple HTML, PostScript or PDF designed for human modification.
Examples of transparent image formats include PNG, XCF and JPG.
Opaque formats include proprietary formats that can be read and
edited only by proprietary word processors, SGML or XML for which
the DTD and/or processing tools are not generally available, and
the machine-generated HTML, PostScript or PDF produced by some word
processors for output purposes only.
The "Title Page" means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the
material this License requires to appear in the title page. For
works in formats which do not have any title page as such, "Title
Page" means the text near the most prominent appearance of the
work's title, preceding the beginning of the body of the text.
The "publisher" means any person or entity that distributes copies
of the Document to the public.
A section "Entitled XYZ" means a named subunit of the Document
whose title either is precisely XYZ or contains XYZ in parentheses
following text that translates XYZ in another language. (Here XYZ
stands for a specific section name mentioned below, such as
"Acknowledgements", "Dedications", "Endorsements", or "History".)
To "Preserve the Title" of such a section when you modify the
Document means that it remains a section "Entitled XYZ" according
to this definition.
The Document may include Warranty Disclaimers next to the notice
which states that this License applies to the Document. These
Warranty Disclaimers are considered to be included by reference in
this License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and
has no effect on the meaning of this License.
2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License
applies to the Document are reproduced in all copies, and that you
add no other conditions whatsoever to those of this License. You
may not use technical measures to obstruct or control the reading
or further copying of the copies you make or distribute. However,
you may accept compensation in exchange for copies. If you
distribute a large enough number of copies you must also follow the
conditions in section 3.
You may also lend copies, under the same conditions stated above,
and you may publicly display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly
have printed covers) of the Document, numbering more than 100, and
the Document's license notice requires Cover Texts, you must
enclose the copies in covers that carry, clearly and legibly, all
these Cover Texts: Front-Cover Texts on the front cover, and
Back-Cover Texts on the back cover. Both covers must also clearly
and legibly identify you as the publisher of these copies. The
front cover must present the full title with all words of the title
equally prominent and visible. You may add other material on the
covers in addition. Copying with changes limited to the covers, as
long as they preserve the title of the Document and satisfy these
conditions, can be treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto
adjacent pages.
If you publish or distribute Opaque copies of the Document
numbering more than 100, you must either include a machine-readable
Transparent copy along with each Opaque copy, or state in or with
each Opaque copy a computer-network location from which the general
network-using public has access to download using public-standard
network protocols a complete Transparent copy of the Document, free
of added material. If you use the latter option, you must take
reasonably prudent steps, when you begin distribution of Opaque
copies in quantity, to ensure that this Transparent copy will
remain thus accessible at the stated location until at least one
year after the last time you distribute an Opaque copy (directly or
through your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of
the Document well before redistributing any large number of copies,
to give them a chance to provide you with an updated version of the
Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document
under the conditions of sections 2 and 3 above, provided that you
release the Modified Version under precisely this License, with the
Modified Version filling the role of the Document, thus licensing
distribution and modification of the Modified Version to whoever
possesses a copy of it. In addition, you must do these things in
the Modified Version:
A. Use in the Title Page (and on the covers, if any) a title
distinct from that of the Document, and from those of previous
versions (which should, if there were any, be listed in the
History section of the Document). You may use the same title
as a previous version if the original publisher of that
version gives permission.
B. List on the Title Page, as authors, one or more persons or
entities responsible for authorship of the modifications in
the Modified Version, together with at least five of the
principal authors of the Document (all of its principal
authors, if it has fewer than five), unless they release you
from this requirement.
C. State on the Title page the name of the publisher of the
Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license
notice giving the public permission to use the Modified
Version under the terms of this License, in the form shown in
the Addendum below.
G. Preserve in that license notice the full lists of Invariant
Sections and required Cover Texts given in the Document's
license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled "History", Preserve its Title,
and add to it an item stating at least the title, year, new
authors, and publisher of the Modified Version as given on the
Title Page. If there is no section Entitled "History" in the
Document, create one stating the title, year, authors, and
publisher of the Document as given on its Title Page, then add
an item describing the Modified Version as stated in the
previous sentence.
J. Preserve the network location, if any, given in the Document
for public access to a Transparent copy of the Document, and
likewise the network locations given in the Document for
previous versions it was based on. These may be placed in the
"History" section. You may omit a network location for a work
that was published at least four years before the Document
itself, or if the original publisher of the version it refers
to gives permission.
K. For any section Entitled "Acknowledgements" or "Dedications",
Preserve the Title of the section, and preserve in the section
all the substance and tone of each of the contributor
acknowledgements and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document, unaltered
in their text and in their titles. Section numbers or the
equivalent are not considered part of the section titles.
M. Delete any section Entitled "Endorsements". Such a section
may not be included in the Modified Version.
N. Do not retitle any existing section to be Entitled
"Endorsements" or to conflict in title with any Invariant
Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no
material copied from the Document, you may at your option designate
some or all of these sections as invariant. To do this, add their
titles to the list of Invariant Sections in the Modified Version's
license notice. These titles must be distinct from any other
section titles.
You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties--for example, statements of peer review or that the text
has been approved by an organization as the authoritative
definition of a standard.
You may add a passage of up to five words as a Front-Cover Text,
and a passage of up to 25 words as a Back-Cover Text, to the end of
the list of Cover Texts in the Modified Version. Only one passage
of Front-Cover Text and one of Back-Cover Text may be added by (or
through arrangements made by) any one entity. If the Document
already includes a cover text for the same cover, previously added
by you or by arrangement made by the same entity you are acting on
behalf of, you may not add another; but you may replace the old
one, on explicit permission from the previous publisher that added
the old one.
The author(s) and publisher(s) of the Document do not by this
License give permission to use their names for publicity for or to
assert or imply endorsement of any Modified Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under
this License, under the terms defined in section 4 above for
modified versions, provided that you include in the combination all
of the Invariant Sections of all of the original documents,
unmodified, and list them all as Invariant Sections of your
combined work in its license notice, and that you preserve all
their Warranty Disclaimers.
The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name
but different contents, make the title of each such section unique
by adding at the end of it, in parentheses, the name of the
original author or publisher of that section if known, or else a
unique number. Make the same adjustment to the section titles in
the list of Invariant Sections in the license notice of the
combined work.
In the combination, you must combine any sections Entitled
"History" in the various original documents, forming one section
Entitled "History"; likewise combine any sections Entitled
"Acknowledgements", and any sections Entitled "Dedications". You
must delete all sections Entitled "Endorsements."
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other
documents released under this License, and replace the individual
copies of this License in the various documents with a single copy
that is included in the collection, provided that you follow the
rules of this License for verbatim copying of each of the documents
in all other respects.
You may extract a single document from such a collection, and
distribute it individually under this License, provided you insert
a copy of this License into the extracted document, and follow this
License in all other respects regarding verbatim copying of that
document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other
separate and independent documents or works, in or on a volume of a
storage or distribution medium, is called an "aggregate" if the
copyright resulting from the compilation is not used to limit the
legal rights of the compilation's users beyond what the individual
works permit. When the Document is included in an aggregate, this
License does not apply to the other works in the aggregate which
are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half
of the entire aggregate, the Document's Cover Texts may be placed
on covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic
form. Otherwise they must appear on printed covers that bracket
the whole aggregate.
8. TRANSLATION
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section
4. Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also
include the original English version of this License and the
original versions of those notices and disclaimers. In case of a
disagreement between the translation and the original version of
this License or a notice or disclaimer, the original version will
prevail.
If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to
Preserve its Title (section 1) will typically require changing the
actual title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document
except as expressly provided under this License. Any attempt
otherwise to copy, modify, sublicense, or distribute it is void,
and will automatically terminate your rights under this License.
However, if you cease all violation of this License, then your
license from a particular copyright holder is reinstated (a)
provisionally, unless and until the copyright holder explicitly and
finally terminates your license, and (b) permanently, if the
copyright holder fails to notify you of the violation by some
reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from
that copyright holder, and you cure the violation prior to 30 days
after your receipt of the notice.
Termination of your rights under this section does not terminate
the licenses of parties who have received copies or rights from you
under this License. If your rights have been terminated and not
permanently reinstated, receipt of a copy of some or all of the
same material does not give you any rights to use it.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of
the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
<http://www.gnu.org/copyleft/>;.
Each version of the License is given a distinguishing version
number. If the Document specifies that a particular numbered
version of this License "or any later version" applies to it, you
have the option of following the terms and conditions either of
that specified version or of any later version that has been
published (not as a draft) by the Free Software Foundation. If the
Document does not specify a version number of this License, you may
choose any version ever published (not as a draft) by the Free
Software Foundation. If the Document specifies that a proxy can
decide which future versions of this License can be used, that
proxy's public statement of acceptance of a version permanently
authorizes you to choose that version for the Document.
11. RELICENSING
"Massive Multiauthor Collaboration Site" (or "MMC Site") means any
World Wide Web server that publishes copyrightable works and also
provides prominent facilities for anybody to edit those works. A
public wiki that anybody can edit is an example of such a server.
A "Massive Multiauthor Collaboration" (or "MMC") contained in the
site means any set of copyrightable works thus published on the MMC
site.
"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.
"Incorporate" means to publish or republish a Document, in whole or
in part, as part of another Document.
An MMC is "eligible for relicensing" if it is licensed under this
License, and if all works that were first published under this
License somewhere other than this MMC, and subsequently
incorporated in whole or in part into the MMC, (1) had no cover
texts or invariant sections, and (2) were thus incorporated prior
to November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the
site under CC-BY-SA on the same site at any time before August 1,
2009, provided the MMC is eligible for relicensing.
ADDENDUM: How to use this License for your documents
====================================================
To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:
Copyright (C) YEAR YOUR NAME.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3
or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the section entitled ``GNU
Free Documentation License''.
If you have Invariant Sections, Front-Cover Texts and Back-Cover
Texts, replace the "with...Texts." line with this:
with the Invariant Sections being LIST THEIR TITLES, with
the Front-Cover Texts being LIST, and with the Back-Cover Texts
being LIST.
If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.
If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of free
software license, such as the GNU General Public License, to permit
their use in free software.
File: libgomp.info, Node: Funding, Next: Library Index, Prev: GNU Free Documentation License, Up: Top
Funding Free Software
*********************
If you want to have more free software a few years from now, it makes
sense for you to help encourage people to contribute funds for its
development. The most effective approach known is to encourage
commercial redistributors to donate.
Users of free software systems can boost the pace of development by
encouraging for-a-fee distributors to donate part of their selling price
to free software developers--the Free Software Foundation, and others.
The way to convince distributors to do this is to demand it and
expect it from them. So when you compare distributors, judge them
partly by how much they give to free software development. Show
distributors they must compete to be the one who gives the most.
To make this approach work, you must insist on numbers that you can
compare, such as, "We will donate ten dollars to the Frobnitz project
for each disk sold." Don't be satisfied with a vague promise, such as
"A portion of the profits are donated," since it doesn't give a basis
for comparison.
Even a precise fraction "of the profits from this disk" is not very
meaningful, since creative accounting and unrelated business decisions
can greatly alter what fraction of the sales price counts as profit. If
the price you pay is $50, ten percent of the profit is probably less
than a dollar; it might be a few cents, or nothing at all.
Some redistributors do development work themselves. This is useful
too; but to keep everyone honest, you need to inquire how much they do,
and what kind. Some kinds of development make much more long-term
difference than others. For example, maintaining a separate version of
a program contributes very little; maintaining the standard version of a
program for the whole community contributes much. Easy new ports
contribute little, since someone else would surely do them; difficult
ports such as adding a new CPU to the GNU Compiler Collection contribute
more; major new features or packages contribute the most.
By establishing the idea that supporting further development is "the
proper thing to do" when distributing free software for a fee, we can
assure a steady flow of resources into making more free software.
Copyright (C) 1994 Free Software Foundation, Inc.
Verbatim copying and redistribution of this section is permitted
without royalty; alteration is not permitted.
File: libgomp.info, Node: Library Index, Prev: Funding, Up: Top
Library Index
*************
* Menu:
* Environment Variable: OMP_CANCELLATION. (line 6)
* Environment Variable <1>: OMP_DISPLAY_ENV. (line 6)
* Environment Variable <2>: OMP_DEFAULT_DEVICE. (line 6)
* Environment Variable <3>: OMP_DYNAMIC. (line 6)
* Environment Variable <4>: OMP_MAX_ACTIVE_LEVELS. (line 6)
* Environment Variable <5>: OMP_MAX_TASK_PRIORITY. (line 6)
* Environment Variable <6>: OMP_NESTED. (line 6)
* Environment Variable <7>: OMP_NUM_THREADS. (line 6)
* Environment Variable <8>: OMP_PROC_BIND. (line 6)
* Environment Variable <9>: OMP_PLACES. (line 6)
* Environment Variable <10>: OMP_STACKSIZE. (line 6)
* Environment Variable <11>: OMP_SCHEDULE. (line 6)
* Environment Variable <12>: OMP_THREAD_LIMIT. (line 6)
* Environment Variable <13>: OMP_WAIT_POLICY. (line 6)
* Environment Variable <14>: GOMP_CPU_AFFINITY. (line 6)
* Environment Variable <15>: GOMP_DEBUG. (line 6)
* Environment Variable <16>: GOMP_STACKSIZE. (line 6)
* Environment Variable <17>: GOMP_SPINCOUNT. (line 6)
* Environment Variable <18>: GOMP_RTEMS_THREAD_POOLS.
(line 6)
* FDL, GNU Free Documentation License: GNU Free Documentation License.
(line 6)
* Implementation specific setting: OMP_NESTED. (line 6)
* Implementation specific setting <1>: OMP_NUM_THREADS. (line 6)
* Implementation specific setting <2>: OMP_SCHEDULE. (line 6)
* Implementation specific setting <3>: GOMP_STACKSIZE. (line 6)
* Implementation specific setting <4>: GOMP_SPINCOUNT. (line 6)
* Implementation specific setting <5>: GOMP_RTEMS_THREAD_POOLS.
(line 6)
* Introduction: Top. (line 6)
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