pthread_cond_signal - Wakes at least one thread that is waiting on the specified condition variable.
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 Interface
Condition variable to be signaled.
This routine unblocks at least one thread waiting on the specified condition variable cond. Calling this routine implies that data guarded by the associated mutex has changed, thus it might be possible for one of the waiting threads to proceed. In general, only one thread will be released.
If no threads are waiting on the specified condition variable, this routine takes no action. The signal does not propagate to the next condition variable wait.
This routine should be called when any thread waiting on the specified condition variable might find its predicate true, but only one thread should proceed. If more than one thread can proceed, or if any thread would not be able to proceed, then you must use pthread_cond_broadcast(3).
The scheduling policy determines which thread is awakened. For policies SCHED_FIFO and SCHED_RR, a blocked thread is chosen in priority order, using first-in/first-out (FIFO) within priorities.
You can call this routine even when the associated mutex is locked. However, if predictable scheduling behavior is required, then that mutex should be locked by the thread calling pthread_cond_signal(3).
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 is invalid.
Functions: pthread_cond_broadcast(3), pthread_cond_destroy(3), pthread_cond_init(3), pthread_cond_timedwait(3), pthread_cond_wait(3)
Manuals: Guide to DECthreads and Programmer's Guide