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PTHREAD_COND_WAIT(3C)					 PTHREAD_COND_WAIT(3C)

NAME
       pthread_cond_wait, pthread_cond_timedwait, pthread_cond_reltimedwait_np
       - wait on a condition

SYNOPSIS
       cc -mt [ flag... ] file... -lpthread [ library... ]
       #include <pthread.h>

       int pthread_cond_wait(pthread_cond_t *restrict cond,
	    pthread_mutex_t *restrict mutex);

       int pthread_cond_timedwait(pthread_cond_t *restrict cond,
	    pthread_mutex_t *restrict mutex,
	    const struct timespec *restrict abstime);

       int pthread_cond_reltimedwait_np(pthread_cond_t *cond,
	    pthread_mutex_t *mutex, const struct timespec *reltime);

DESCRIPTION
       The	pthread_cond_wait(),	   pthread_cond_timedwait(),	   and
       pthread_cond_reltimedwait_np()  functions are used to block on a condi‐
       tion variable. They are called with mutex locked by the calling	thread
       or undefined behavior will result.

       These  functions	 atomically release mutex and cause the calling thread
       to block on the condition variable cond. Atomically here means ``atomi‐
       cally  with  respect to access by another  thread to the mutex and then
       the condition variable." That is, if another thread is able to  acquire
       the  mutex after the about-to-block thread has released it, then a sub‐
       sequent call to pthread_cond_signal()  or  pthread_cond_broadcast()  in
       that  thread  behaves  as  if  it  were issued after the about-to-block
       thread has blocked.

       Upon successful return, the mutex has been locked and is owned  by  the
       calling	thread.	 If  mutex is a robust mutex where an owner terminated
       while holding the lock and the  state  is  recoverable,	the  mutex  is
       acquired even though the function returns an error value.

       When  using condition variables there is always a boolean predicate, an
       invariant, associated with each condition wait that must be true before
       the    thread	should	  proceed.    Spurious	  wakeups   from   the
       pthread_cond_wait(),  pthread_cond_timedwait(),	or   pthread_cond_rel‐
       timedwait_np()	functions   could   occur.   Since   the  return  from
       pthread_cond_wait(),  pthread_cond_timedwait(),	or   pthread_cond_rel‐
       timedwait_np()  does  not imply anything about the value of this predi‐
       cate, the predicate should always be reevaluated.

       The order in which blocked threads are  awakened	 by  pthread_cond_sig‐
       nal()  or pthread_cond_broadcast() is determined by the scheduling pol‐
       icy. See pthreads(5).

       The  effect   of	  using	  more	 than	one   mutex   for   concurrent
       pthread_cond_wait(),   pthread_cond_timedwait(),	 or  pthread_cond_rel‐
       timedwait_np() operations on the same condition variable will result in
       undefined behavior.

       A  condition  wait (whether timed or not) is a cancellation point. When
       the cancelability enable state of  a  thread  is	 set  to  PTHREAD_CAN‐
       CEL_DEFERRED, a side effect of acting upon a cancellation request while
       in a condition wait is that the mutex is reacquired before calling  the
       first cancellation cleanup handler.

       A  thread  that	has  been unblocked because it has been canceled while
       blocked in a call to  pthread_cond_wait()  or  pthread_cond_timedwait()
       does not consume any condition signal that may be directed concurrently
       at the condition variable if there are other  threads  blocked  on  the
       condition variable.

       The     pthread_cond_timedwait()	   function    is    the    same    as
       pthread_cond_wait() except that an error is returned  if	 the  absolute
       time  specified	by  abstime  passes  (that  is,	 system time equals or
       exceeds abstime) before the condition cond is signaled or broadcast, or
       if  the	absolute  time specified by abstime has already been passed at
       the time of the call. The abstime argument is of type struct  timespec,
       defined	   in	 time.h(3HEAD).	   When	   such	   time-outs	occur,
       pthread_cond_timedwait() will nonetheless  release  and	reacquire  the
       mutex  referenced  by  mutex.  The function pthread_cond_timedwait() is
       also a cancellation point.

       The pthread_cond_reltimedwait_np() function is a non-standard extension
       provided	 by  the  Solaris version of POSIX threads as indicated by the
       ``_np'' (non-portable) suffix. The pthread_cond_reltimedwait_np() func‐
       tion  is	 the  same as pthread_cond_timedwait() except that the reltime
       argument specifies a non-negative time relative to the  current	system
       time  rather  than  an  absolute	 time. The reltime argument is of type
       struct timespec, defined in time.h(3HEAD). An error value  is  returned
       if the relative time passes (that is, system time equals or exceeds the
       starting system time plus the relative time) before the condition  cond
       is  signaled or broadcast.  When such timeouts occur, pthread_cond_rel‐
       timedwait_np() releases and reacquires the mutex referenced  by	mutex.
       The  pthread_cond_reltimedwait_np()  function  is  also	a cancellation
       point.

       If a signal is delivered to a thread waiting for a condition  variable,
       upon  return from the signal handler the thread resumes waiting for the
       condition variable as if it was not interrupted, or it returns 0 due to
       spurious wakeup.

RETURN VALUES
       Except in the case of ETIMEDOUT, EOWNERDEAD, or ENOTRECOVERABLE, all of
       these error checks act as if they were  performed  immediately  at  the
       beginning  of processing for the function and cause an error return, in
       effect, prior to modifying the state of the mutex specified by mutex or
       the condition variable specified by cond.

       Upon successful completion, 0 is returned. Otherwise, an error value is
       returned to indicate the error.

ERRORS
       These functions will fail if:

       EPERM
		The mutex type is PTHREAD_MUTEX_ERRORCHECK or the mutex	 is  a
		robust mutex, and the current thread does not own the mutex.

       The  pthread_cond_timedwait() function will fail if:

       ETIMEDOUT
		    The	   absolute    time    specified    by	  abstime   to
		    pthread_cond_timedwait() has passed.

       The pthread_cond_reltimedwait_np() function will fail if:

       EINVAL
		    The value specified by reltime is invalid.

       ETIMEDOUT
		    The	  relative    time    specified	   by	 reltime    to
		    pthread_cond_reltimedwait_np() has passed.

       These functions may fail if:

       EINVAL
		 The  value  specified	by cond, mutex, abstime, or reltime is
		 invalid.

       EINVAL
		 Different mutexes were supplied for concurrent operations  on
		 the same condition variable.

       If the mutex specified by mutex is a robust mutex (initialized with the
       robustness attribute  PTHREAD_MUTEX_ROBUST),  the  pthread_cond_wait(),
       pthread_cond_timedwait(),  and pthread_cond_reltimedwait_np() functions
       will, under the specified conditions, return the following  error  val‐
       ues.   For  complete  information,  see	the pthread_mutex_lock(3C) and
       pthread_mutexattr_setrobust(3C) manual pages.

       EOWNERDEAD
			  The last owner of this mutex died while holding  the
			  mutex,  leaving the state it was protecting possibly
			  inconsistent. The mutex is now owned by the caller.

       ENOTRECOVERABLE
			  The mutex was protecting state  that	has  now  been
			  left irrecoverable. The mutex has not been acquired.

ATTRIBUTES
       See attributes(5) for descriptions of the following attributes:

       ┌────────────────────┬─────────────────┐
       │  ATTRIBUTE TYPE    │ ATTRIBUTE VALUE │
       ├────────────────────┼─────────────────┤
       │Interface Stability │ Standard	      │
       ├────────────────────┼─────────────────┤
       │MT-Level	    │ MT-Safe	      │
       └────────────────────┴─────────────────┘

SEE ALSO
       pthread_cond_signal(3C),			   pthread_cond_broadcast(3C),
       pthread_mutex_lock(3C), pthread_mutexattr_getrobust(3C), time.h(3HEAD),
       attributes(5), condition(5), pthreads(5), standards(5)

				 Nov 11, 2008		 PTHREAD_COND_WAIT(3C)
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