pthread_cond_signal(3)pthread_cond_signal(3)NAMEpthread_cond_signal - Wakes at least one thread that is waiting on the
specified condition variable
SYNOPSIS
#include <pthread.h>
int pthread_cond_signal(
pthread_cond_t *cond );
LIBRARY
DECthreads POSIX 1003.1c Library (libpthread.so)
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
IEEE Std 1003.1c-1995, POSIX System Application Program Interface
PARAMETERS
Condition variable to be signaled.
DESCRIPTION
This routine unblocks at least one thread waiting on the specified con‐
dition 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 con‐
dition 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) within priorities.
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 mutex.
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 is not a valid con‐
dition variable.
ERRORS
None
SEE ALSO
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
pthread_cond_signal(3)