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

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 con-
       dition variable attributes object. Upon successful initialization, the state of the condi-
       tion 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
       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(&rp->notbusy);
               free(ep);
           }

       In this example, the condition variable and its list element may be freed (line B) immedi-
       ately 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 recom-
       mended 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 initial-
       ized 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().

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 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 discrep-
       ancy 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(3POSIX)