pthread_cond_signal - Wakes at least one thread that is
waiting on the specified condition variable
pthread_cond_t *cond );
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
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
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 of the threads 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)
If the calling thread holds the lock to the target condition
variable's associated mutex while setting the variable's
wait predicate, that thread can call
pthread_cond_signal(3) to signal the variable even after
releasing the lock on that mutex. However, for more predictable
scheduling behavior, call pthread_cond_signal(3)
before releasing the target condition variable's associated
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 not a valid condition variable.
Manuals: Guide to DECthreads and Programmer's Guide
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