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PTHREAD_GETCONCURRENCY(3P) POSIX Programmer's ManualPTHREAD_GETCONCURRENCY(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
NAME
       pthread_getconcurrency, pthread_setconcurrency - get and set the  level
       of concurrency
SYNOPSIS
       #include <pthread.h>
       int pthread_getconcurrency(void);
       int pthread_setconcurrency(int new_level);

DESCRIPTION
       Unbound  threads in a process may or may not be required to be simulta-
       neously active. By default, the threads implementation ensures  that  a
       sufficient  number  of  threads are active so that the process can con-
       tinue to make progress. While this conserves system resources,  it  may
       not produce the most effective level of concurrency.
       The  pthread_setconcurrency()  function allows an application to inform
       the threads implementation of its desired concurrency level, new_level.
       The  actual  level  of  concurrency provided by the implementation as a
       result of this function call is unspecified.
       If new_level is zero, it causes the implementation to maintain the con-
       currency  level  at  its  discretion as if pthread_setconcurrency() had
       never been called.
       The pthread_getconcurrency() function shall return the value set  by  a
       previous   call   to  the  pthread_setconcurrency()  function.  If  the
       pthread_setconcurrency() function was not previously called, this func-
       tion shall return zero to indicate that the implementation is maintain-
       ing the concurrency level.
       A call to pthread_setconcurrency() shall inform the  implementation  of
       its  desired  concurrency level. The implementation shall use this as a
       hint, not a requirement.
       If an implementation does not support multiplexing of user  threads  on
       top  of several kernel-scheduled entities, the pthread_setconcurrency()
       and pthread_getconcurrency() functions are  provided  for  source  code
       compatibility  but  they  shall have no effect when called. To maintain
       the  function  semantics,  the  new_level  parameter  is   saved   when
       pthread_setconcurrency()  is  called  so  that  a  subsequent  call  to
       pthread_getconcurrency() shall return the same value.
RETURN VALUE
       If successful, the pthread_setconcurrency() function shall return zero;
       otherwise, an error number shall be returned to indicate the error.
       The  pthread_getconcurrency()  function shall always return the concur-
       rency level set by a previous call to pthread_setconcurrency(). If  the
       pthread_setconcurrency()  function  has never been called, pthread_get-
       concurrency() shall return zero.
ERRORS
       The pthread_setconcurrency() function shall fail if:
       EINVAL The value specified by new_level is negative.
       EAGAIN The value specific by new_level would cause a system resource to
              be exceeded.

       These functions shall not return an error code of [EINTR].
       The following sections are informative.
EXAMPLES
       None.
APPLICATION USAGE
       Use  of these functions changes the state of the underlying concurrency
       upon which the application depends. Library developers are  advised  to
       not use the pthread_getconcurrency() and pthread_setconcurrency() func-
       tions since their use may conflict with an applications  use  of  these
       functions.
RATIONALE
       None.
FUTURE DIRECTIONS
       None.
SEE ALSO
       The Base Definitions volume of IEEE Std 1003.1-2001, <pthread.h>
COPYRIGHT
       Portions  of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       --  Portable  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  of
       Electrical  and  Electronics  Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE and
       The  Open Group Standard, the original IEEE and The Open Group Standard
       is the referee document. The original Standard can be  obtained  online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003           PTHREAD_GETCONCURRENCY(3P)