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PTHREAD_COND_DESTROY(3P) POSIX Programmer's Manual PTHREAD_COND_DESTROY(3P)
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.
pthread_cond_destroy, pthread_cond_init — destroy and initialize
condition variables
#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;
The pthread_cond_destroy() function shall destroy the given condition
variable specified by cond; the object becomes, in effect,
uninitialized. 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
condition variable upon which other threads are currently blocked
results in undefined behavior.
The pthread_cond_init() function shall initialize the condition
variable 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 variable 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_broadcast(), 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
variable attributes object.
If successful, the pthread_cond_destroy() and pthread_cond_init()
functions shall return zero; otherwise, an error number shall be
returned to indicate the error.
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.
A condition variable can be destroyed immediately after all the
threads that are blocked on it are awakened. For example, consider
the following 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
awakened (line A), since the mutex and the code ensure that no other
thread can touch the element to be deleted.
None.
If an implementation detects that the value specified by the cond
argument to pthread_cond_destroy() does not refer to an initialized
condition 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
argument to pthread_cond_destroy() or pthread_cond_init() refers to a
condition 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
argument 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(3p).
None.
pthread_cond_broadcast(3p), pthread_cond_timedwait(3p),
pthread_mutex_destroy(3p)
The Base Definitions volume of POSIX.1‐2008, pthread.h(0p)
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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 PTHREAD_COND_DESTROY(3P)
Pages that refer to this page: pthread.h(0p), pthread_condattr_destroy(3p), pthread_condattr_getclock(3p), pthread_condattr_getpshared(3p), pthread_cond_broadcast(3p), pthread_mutexattr_destroy(3p), pthread_mutexattr_getprioceiling(3p), pthread_mutexattr_getprotocol(3p), pthread_mutexattr_getpshared(3p)