Open System Services System Calls Reference Manual (G06.25+, H06.03+)

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pthread_cond_wait(2) OSS System Calls Reference Manual

NAME

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

or broadcast

LIBRARY

G-series native OSS processes: /G/system/sysnn/zsptsrl

H-series OSS processes: /G/system/zdllnnn/zsptdll

SYNOPSIS

#include <spthread.h>

int pthread_cond_wait(

pthread_cond_t *cond,

pthread_mutex_t *mutex );

PARAMETERS

cond speciﬁes the condition variable that the calling thread waits on.

mutex speciﬁes the mutex associated with the condition variable speciﬁed by the cond

parameter.

DESCRIPTION

This function causes a thread to wait for the speciﬁed condition variable to be signaled or broad-

cast. 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, return from this function does not imply anything about the value of the

predicate, and it should be reevaluated upon return.

This function atomically releases the mutex and causes the calling thread to wait on the condi-

tion variable. When the thread regains control after calling pthread_cond_wait(), the mutex is

locked and the thread is the owner, 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).

If a thread 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, that thread must call either the

pthread_cond_signal( ) or pthread_cond_broadcast( ) function for that condition variable. If

neither call is made, any thread waiting on the condition variable continues to wait.

This function might (with low probability) return when the condition variable has not been sig-

naled or broadcast. When this occurs, the mutex is reacquired before the function returns. To

handle this type of situation, enclose each call to this function in a loop that checks the predicate.

The loop documents your intent and protects against spurious wakeups while allowing correct

behavior even if another thread consumes the desired state before the awakened thread runs.

Threads are not allowed to wait on the same condition variable by specifying different mutexes.

Call this function after you have locked the mutex speciﬁed by mutex. The results of this func-

tion are unpredictable if this function is called before the mutex is locked.

RETURN VALUES

If an error condition occurs, this function returns an integer value indicating the type of error.

Possible return values are:

0 Successful completion.

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