NAME    [Toc]    [Back]

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

SYNOPSIS    [Toc]    [Back]

       #include <pthread.h>

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

LIBRARY    [Toc]    [Back]

       DECthreads POSIX 1003.1c Library (libpthread.so)

STANDARDS    [Toc]    [Back]

       Interfaces documented on this reference  page  conform  to
       industry standards as follows:

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

PARAMETERS    [Toc]    [Back]

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

DESCRIPTION    [Toc]    [Back]

       This routine causes a thread to  wait  for  the  specified
       condition  variable  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 cancelability
       is  enabled, the thread reacquires the mutex (blocking for
       it if necessary) before the cleanup handlers are  run  (or
       before the exception 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
  cancelability  enabled  are  those which disable
       asynchronous cancelability.

RETURN VALUES    [Toc]    [Back]

       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    [Toc]    [Back]

       None

SEE ALSO    [Toc]    [Back]

       Functions:                      pthread_cond_broadcast(3),
       pthread_cond_destroy(3),             pthread_cond_init(3),
       pthread_cond_signal(3), pthread_cond_timedwait(3),

       Manuals: Guide to DECthreads and Programmer's Guide



                                             pthread_cond_wait(3)