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man pages section 3: Basic Library Functions

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Updated: Wednesday, July 27, 2022



pthread_cond_signal, pthread_cond_broadcast - signal or broadcast a condition


#include <pthread.h>

int pthread_cond_signal(pthread_cond_t *cond);
int pthread_cond_broadcast(pthread_cond_t *cond);


These two functions are used to unblock threads blocked on a condition variable.

The pthread_cond_signal() call unblocks at least one of the threads that are blocked on the specified condition variable cond (if any threads are blocked on cond).

The pthread_cond_broadcast() call unblocks all threads currently blocked on the specified condition variable cond.

If more than one thread is blocked on a condition variable, the scheduling policy determines the order in which threads are unblocked. When each thread unblocked as a result of a pthread_cond_signal() or pthread_cond_broadcast() returns from its call to pthread_cond_wait() or pthread_cond_timedwait(), the thread owns the mutex with which it called pthread_cond_wait() or pthread_cond_timedwait(). The thread(s) that are unblocked contend for the mutex according to the scheduling policy (if applicable), and as if each had called pthread_mutex_lock().

The pthread_cond_signal() or pthread_cond_broadcast() functions may be called by a thread whether or not it currently owns the mutex that threads calling pthread_cond_wait() or pthread_cond_timedwait() have associated with the condition variable during their waits; however, if predictable scheduling behavior is required, then that mutex is locked by the thread calling pthread_cond_signal() or pthread_cond_broadcast().

The pthread_cond_signal() and pthread_cond_broadcast() functions have no effect if there are no threads currently blocked on cond.

Return Values

If successful, the pthread_cond_signal() and pthread_cond_broadcast() functions return 0. Otherwise, an error number is returned to indicate the error.


The pthread_cond_signal() and pthread_cond_broadcast() function may fail if:


The value cond does not refer to an initialized condition variable.


See attributes(7) for descriptions of the following attributes:

Interface Stability

See Also

pthread_cond_init(3C), pthread_cond_timedwait(3C), pthread_cond_wait(3C), attributes(7), condition(7), standards(7)