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



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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().

FUTURE DIRECTIONS
       None.

SEE ALSO
       pthread__cond__broadcast(), pthread__cond__timedwait(),
       pthread__mutex__destroy()

       The Base Definitions volume of POSIX.1-2017, <pthread.h>

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_COND_DESTROY(3)
