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



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 condi-
       tion 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 that are statically allocated. The effect shall be equivalent
       to dynamic initialization by a call to pthread_cond_init() with parame-
       ter  attr specified as NULL, except that no error checks are performed.

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.

       The [EBUSY] and [EINVAL] error checks, if implemented, shall act as  if
       they  were performed immediately at the beginning of processing for the
       function and caused an error return prior to modifying the state of the
       condition variable specified by cond.

ERRORS
       The pthread_cond_destroy() function may fail if:

       EBUSY  The implementation has detected an attempt to destroy the object
	      referenced by cond while it is referenced	 (for  example,	 while
	      being used in a pthread_cond_wait() or pthread_cond_timedwait())
	      by another thread.

       EINVAL The value specified by cond is invalid.


       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.


       The pthread_cond_init() function may fail if:

       EBUSY  The implementation has detected an attempt to  reinitialize  the
	      object referenced by cond, a previously initialized, but not yet
	      destroyed, condition variable.

       EINVAL The value specified by attr is invalid.


       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
       See  pthread_mutex_init()  ;  a	similar rationale applies to condition
       variables.

FUTURE DIRECTIONS
       None.

SEE ALSO
       pthread_cond_broadcast() , pthread_cond_signal() ,  pthread_cond_timed-
       wait()	,   the	  Base	Definitions  volume  of	 IEEE Std 1003.1-2001,
       <pthread.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 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 .



IEEE/The Open Group		     2003	       PTHREAD_COND_DESTROY(P)
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