pthread_cond_wait(3) Library Functions Manual pthread_cond_wait(3)
NAME
pthread_cond_wait - Causes a thread to wait for the specified condition variable to be signaled or broadcasted.
LIBRARY
DECthreads POSIX 1003.1c Library (libpthread.so)
SYNOPSIS
#include <pthread.h>
int pthread_cond_wait(
pthread_cond_t *cond,
pthread_mutex_t *mutex);
STANDARDS
Interfaces documented on this reference page conform to industry standards 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 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
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 vari-
able.
ERRORS
None
RELATED INFORMATION
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
delim off
pthread_cond_wait(3)