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);

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

       These functions atomically release mutex and cause the calling thread to block on  the  condition  variable  cond.  Atomically  here  means
       ``atomically  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  subsequent  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.

       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_reltimed-
       wait_np()  functions may occur. Since the return from pthread_cond_wait(), pthread_cond_timedwait(), or pthread_cond_reltimedwait_np() does
       not imply anything about the value of this predicate, the predicate should always be re-evaluated.

       The order in which blocked threads are awakened by pthread_cond_signal() 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_reltimedwait_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 re-acquired 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 broadcasted, or if the absolute
       time specified by abstime has already been passed at the time of the call. When such time-outs occur, pthread_cond_timedwait()  will  none-
       theless 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 pthreads as indicated by the
       ``_np'' (non-portable) suffix. The pthread_cond_reltimedwait_np() function 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. 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  broadcasted.  When such timeouts occur, pthread_cond_reltimedwait_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.

       Except  in  the	case of ETIMEDOUT, all 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 spec-
       ified by cond.

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

       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.

       The pthread_cond_wait() and pthread_cond_timedwait() functions may fail if:

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

       EINVAL	       Different mutexes were supplied for concurrent pthread_cond_wait() or pthread_cond_timedwait(), operations on the same con-
		       dition variable.

       EPERM	       The mutex was not owned by the current thread at the time of the call.

       When  a	thread	makes  a  call	to  pthread_cond_wait(),  pthread_cond_timedwait(),  or  pthread_cond_reltimedwait_np(),  if  the   symbol
       _POSIX_THREAD_PRIO_INHERIT  is  defined	and the mutex is initialized with the protocol attribute having the value PTHREAD_PRIO_INHERIT and
       the robustness attribute having	the  value  PTHREAD_MUTEX_ROBUST_NP  (see  pthread_mutexattr_getrobust_np(3C)),  the  pthread_cond_wait(),
       pthread_cond_timedwait(), and pthread_cond_reltimedwait_np() functions will fail if:

       EOWNERDEAD	       The  last  owner of this mutex died while holding the mutex. This mutex is now owned by the caller. The caller must
			       now attempt to make the state protected by the mutex consistent. If it is able to  clean  up  the  state,  then	it
			       should	call   pthread_mutex_consistent_np()   for   the   mutex   and	unlock	the  mutex.  Subsequent  calls	to
			       pthread_cond_wait(), pthread_cond_timedwait(), and pthread_cond_reltimedwait_np() will behave normally, as  before.
			       If  the caller is not able to clean up the state, pthread_mutex_consistent_np() should not be called for the mutex,
			       but it should be unlocked. Subsequent calls to pthread_cond_wait(), pthread_cond_timedwait(), and pthread_cond_rel-
			       timedwait_np()  will  fail to acquire the mutex with the error value ENOTRECOVERABLE. If the owner who acquired the
			       lock with EOWNERDEAD dies, the next owner will acquire the lock with EOWNERDEAD.

       ENOTRECOVERABLE	       The mutex trying to be acquired is protecting the state that has been left irrecoverable by the mutex's last owner,
			       who died while holding the lock. The mutex has not been acquired. This condition can occur when the lock was previ-
			       ously acquired with EOWNERDEAD, and the owner was not able to clean up the state and  unlocked  the  mutex  without
			       making the mutex consistent.

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

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

       pthread_cond_signal(3C), pthread_cond_broadcast(3C), attributes(5), condition(5), pthreads(5), standards(5)

								    23 Mar 2005 					     pthread_cond_wait(3C)