PTHREAD_COND_DESTROY(3P) POSIX Programmer's Manual PTHREAD_COND_DESTROY(3P)
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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_cond_destroy, pthread_cond_init -- destroy and initialize con-
dition variables
SYNOPSIS
#include <pthread.h>
int pthread_cond_destroy(pthread_cond_t *cond);
int pthread_cond_init(pthread_cond_t *restrict cond,
const pthread_condattr_t *restrict attr);
pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
DESCRIPTION
The pthread_cond_destroy() function shall destroy the given condition
variable specified by cond; the object becomes, in effect, uninitial-
ized. An implementation may cause pthread_cond_destroy() to set the
object referenced by cond to an invalid value. A destroyed condition
variable object can be reinitialized using pthread_cond_init(); the
results of otherwise referencing the object after it has been destroyed
are undefined.
It shall be safe to destroy an initialized condition variable upon
which no threads are currently blocked. Attempting to destroy a condi-
tion variable upon which other threads are currently blocked results in
undefined behavior.
The pthread_cond_init() function shall initialize the condition vari-
able referenced by cond with attributes referenced by attr. If attr is
NULL, the default condition variable attributes shall be used; the
effect is the same as passing the address of a default condition vari-
able attributes object. Upon successful initialization, the state of
the condition variable shall become initialized.
Only cond itself may be used for performing synchronization. The result
of referring to copies of cond in calls to pthread_cond_wait(),
pthread_cond_timedwait(), pthread_cond_signal(), pthread_cond_broad-
cast(), and pthread_cond_destroy() is undefined.
Attempting to initialize an already initialized condition variable
results in undefined behavior.
In cases where default condition variable attributes are appropriate,
the macro PTHREAD_COND_INITIALIZER can be used to initialize condition
variables. The effect shall be equivalent to dynamic initialization by
a call to pthread_cond_init() with parameter attr specified as NULL,
except that no error checks are performed.
The behavior is undefined if the value specified by the cond argument
to pthread_cond_destroy() does not refer to an initialized condition
variable.
The behavior is undefined if the value specified by the attr argument
to pthread_cond_init() does not refer to an initialized condition vari-
able attributes object.
RETURN VALUE
If successful, the pthread_cond_destroy() and pthread_cond_init() func-
tions shall return zero; otherwise, an error number shall be returned
to indicate the error.
ERRORS
The pthread_cond_init() function shall fail if:
EAGAIN The system lacked the necessary resources (other than memory) to
initialize another condition variable.
ENOMEM Insufficient memory exists to initialize the condition variable.
These functions shall not return an error code of [EINTR].
The following sections are informative.
EXAMPLES
A condition variable can be destroyed immediately after all the threads
that are blocked on it are awakened. For example, consider the follow-
ing code:
struct list {
pthread_mutex_t lm;
...
}
struct elt {
key k;
int busy;
pthread_cond_t notbusy;
...
}
/* Find a list element and reserve it. */
struct elt *
list_find(struct list *lp, key k)
{
struct elt *ep;
pthread_mutex_lock(&lp->lm);
while ((ep = find_elt(l, k) != NULL) && ep->busy)
pthread_cond_wait(&ep->notbusy, &lp->lm);
if (ep != NULL)
ep->busy = 1;
pthread_mutex_unlock(&lp->lm);
return(ep);
}
delete_elt(struct list *lp, struct elt *ep)
{
pthread_mutex_lock(&lp->lm);
assert(ep->busy);
... remove ep from list ...
ep->busy = 0; /* Paranoid. */
(A) pthread_cond_broadcast(&ep->notbusy);
pthread_mutex_unlock(&lp->lm);
(B) pthread_cond_destroy(&rp->notbusy);
free(ep);
}
In this example, the condition variable and its list element may be
freed (line B) immediately after all threads waiting for it are awak-
ened (line A), since the mutex and the code ensure that no other thread
can touch the element to be deleted.
APPLICATION USAGE
None.
RATIONALE
If an implementation detects that the value specified by the cond argu-
ment to pthread_cond_destroy() does not refer to an initialized condi-
tion variable, it is recommended that the function should fail and
report an [EINVAL] error.
If an implementation detects that the value specified by the cond argu-
ment to pthread_cond_destroy() or pthread_cond_init() refers to a con-
dition variable that is in use (for example, in a pthread_cond_wait()
call) by another thread, or detects that the value specified by the
cond argument to pthread_cond_init() refers to an already initialized
condition variable, it is recommended that the function should fail and
report an [EBUSY] error.
If an implementation detects that the value specified by the attr argu-
ment to pthread_cond_init() does not refer to an initialized condition
variable attributes object, it is recommended that the function should
fail and report an [EINVAL] error.
See also pthread_mutex_destroy().
FUTURE DIRECTIONS
None.
SEE ALSO
pthread_cond_broadcast(), pthread_cond_timedwait(),
pthread_mutex_destroy()
The Base Definitions volume of POSIX.1-2008, <pthread.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri-
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the source
files to man page format. To report such errors, see https://www.ker-
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 PTHREAD_COND_DESTROY(3P)
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