pthread_cond_destroy(3p) — Linux manual page

PTHREAD_..._DESTROY(3P) POSIX Programmer's ManualPTHREAD_..._DESTROY(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_cond_destroy, pthread_cond_init — destroy and initialize
       condition 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, 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.

       See Section 2.9.9, Synchronization Object Copies and Alternative
       Mappings for further requirements.

       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.

RETURN VALUE

       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.

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 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(&ep->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.

APPLICATION USAGE

       None.

RATIONALE

       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).

FUTURE DIRECTIONS

       None.

SEE ALSO

       pthread_cond_broadcast(3p), pthread_cond_timedwait(3p),
       pthread_mutex_destroy(3p)

       The Base Definitions volume of POSIX.1‐2017, pthread.h(0p)

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 .

       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               2017           PTHREAD_..._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)

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