Provided by: manpages-posix-dev_2013a-2_all bug

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.

       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)
       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().

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
       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 .