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pthread_cond_wait(3)					  pthread_cond_wait(3)

NAME
       pthread_cond_wait - Causes a thread to wait for the specified condition
       variable to be signaled or broadcasted

SYNOPSIS
       #include <pthread.h>

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

LIBRARY
       DECthreads POSIX 1003.1c Library (libpthread.so)

STANDARDS
       Interfaces documented on this reference page conform to industry	 stan‐
       dards as follows:

       IEEE Std 1003.1c-1995, POSIX System Application Program Interface

PARAMETERS
       Condition  variable that the calling thread waits on.  Mutex associated
       with the condition variable specified in cond.

DESCRIPTION
       This routine causes a thread to wait for the specified condition	 vari‐
       able  to	 be signaled or broadcasted. Each condition corresponds to one
       or more Boolean relations, called a predicate, based  on	 shared	 data.
       The  calling  thread waits for the data to reach a particular state for
       the predicate to become true. However, the  return  from	 this  routine
       does not imply anything about the value of the predicate, and it should
       be reevaluated upon return.

       Call this routine after you have locked the mutex specified  in	mutex.
       The results of this routine are unpredictable if this routine is called
       without first locking the mutex.

       This routine atomically releases	 the  mutex  and  causes  the  calling
       thread  to wait on the condition. When the thread regains control after
       calling pthread_cond_wait(3), the mutex is locked and the thread is the
       owner. This is true regardless of why the wait ended. If general cance‐
       lability is enabled, the thread reacquires the mutex (blocking  for  it
       if necessary) before the cleanup handlers are run (or before the excep‐
       tion is raised).

       A thread that changes the state of storage protected by	the  mutex  in
       such  a way that a predicate associated with a condition variable might
       now   be	  true,	  must	 call	either	  pthread_cond_signal(3)    or
       pthread_cond_broadcast(3)  for that condition variable. If neither call
       is made, any thread waiting on  the  condition  variable	 continues  to
       wait.

       This  routine  might  (with  low probability) return when the condition
       variable has not been signaled or broadcasted. When  this  occurs,  the
       mutex  is reacquired before the routine returns. To handle this type of
       situation, enclose each call to this routine in a loop that checks  the
       predicate.  The loop provides documentation of your intent and protects
       against these spurious wakeups, while also  allowing  correct  behavior
       even  if	 another thread consumes the desired state before the awakened
       thread runs.

       It is illegal for threads to wait on the	 same  condition  variable  by
       specifying different mutexes.

       The  only routines which are supported for use with asynchronous cance‐
       lability enabled are those which disable asynchronous cancelability.

RETURN VALUES
       If an error condition occurs, this routine  returns  an	integer	 value
       indicating  the	type  of error. Possible return values are as follows:
       Successful completion.  The  value  specified  by  cond,	 or  mutex  is
       invalid,	  or:	Different   mutexes   are   supplied   for  concurrent
       pthread_cond_wait(3) operations or pthread_cond_timedwait operations on
       the same condition variable, or: The mutex was not owned by the calling
       thread at the time of  the  call.   DECthreads  cannot  acquire	memory
       needed to block using a statically initialized condition variable.

ERRORS
       None

SEE ALSO
       Functions:      pthread_cond_broadcast(3),     pthread_cond_destroy(3),
       pthread_cond_init(3),	pthread_cond_signal(3),	   pthread_cond_timed‐
       wait(3),

       Manuals: Guide to DECthreads and Programmer's Guide

							  pthread_cond_wait(3)
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