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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.

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 .

IEEE/The Open Group                                   2013                          PTHREAD_COND_DESTROY(3POSIX)