pthread_cond_wait - Causes a thread to wait for the specified
condition variable to be signaled or broadcasted
pthread_mutex_t *mutex );
DECthreads POSIX 1003.1c Library (libpthread.so)
Interfaces documented on this reference page conform to
industry standards as follows:
IEEE Std 1003.1c-1995, POSIX System Application Program
Condition variable that the calling thread waits on.
Mutex associated with the condition variable specified in
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
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
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
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.
Manuals: Guide to DECthreads and Programmer's Guide
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