pthread_cond_wait

Causes a thread to wait for a condition variable to be signaled or broadcasted.

Syntax

pthread_cond_wait( cond, mutex );

Argument Data Type Access

cond opaque pthread_cond_t read mutex opaque pthread_mutex_t read

C Binding

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

Arguments

cond: Condition variable waited on.
mutex: Mutex associated with the condition variable specified in cond.

Description

This routine causes a thread to wait for a condition variable to be signaled or broadcasted. Each condition corresponds to one or more Boolean relations (predicates) based on shared data. The calling thread waits for the data to reach a particular state (for the predicate to become true).

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. If the wait is satisfied as a result of some thread calling pthread_cond_signal or pthread_cond_ broadcast, the mutex is reacquired and the routine returns.

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 or pthread_ cond_broadcast 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 this routine in a loop that checks the predicate.)

Return Values

If an error condition occurs, this routine returns -1 and errno is set to the corresponding error value. Possible return values are as follows:

Return Error Description

0 Successful completion. -1 [EINVAL] The value specified by cond or mutex is invalid. Different mutexes are supplied for concurrent pthread_cond_wait or pthread_cond_timedwait operations.