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



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  con-
       dition 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,  uninitial-
       ized.  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	condi-
       tion variable upon which other threads are currently blocked results in
       undefined behavior.

       The pthread_cond_init() function shall initialize the  condition	 vari-
       able 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 vari-
       able 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_broad-
       cast(), 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 vari-
       able attributes object.

RETURN VALUE
       If successful, the pthread_cond_destroy() and pthread_cond_init() func-
       tions 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 follow-
       ing 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 awak-
       ened (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 argu-
       ment to pthread_cond_destroy() does not refer to an initialized	condi-
       tion  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 argu-
       ment  to pthread_cond_destroy() or pthread_cond_init() refers to a con-
       dition 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 argu-
       ment  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 Electri-
       cal 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.ker-
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IEEE/The Open Group		     2013	      PTHREAD_COND_DESTROY(3P)