PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

PTHREAD_COND_DESTROY(3P)  POSIX Programmer's Manual PTHREAD_COND_DESTROY(3P)

PROLOG         top

       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         top

       pthread_cond_destroy, pthread_cond_init — destroy and initialize
       condition variables

SYNOPSIS         top

       #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         top

       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.

RETURN VALUE         top

       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         top

       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         top

       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.

APPLICATION USAGE         top

       None.

RATIONALE         top

       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         top

       None.

SEE ALSO         top

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

       The Base Definitions volume of POSIX.1‐2008, pthread.h(0p)

COPYRIGHT         top

       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)