pthread_cond_signal

Wakes at least one thread that is waiting on a condition variable.

Syntax

pthread_cond_signal( cond );

Argument Data Type Access

cond opaque pthread_cond_t modify

C Binding

#include 


int
pthread_cond_signal (
         pthread_cond_t   *cond);

Arguments

cond: Condition variable to be signaled.

Description

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, so that it might be possible for one of the waiting threads to proceed. In general, only one will be released.

If no threads are waiting on the specified condition variable, then 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.

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.

Return Values

If an error condition occurs, this routine returns an integer value indicating the type of error. Possible return values are as follows:

Return Description

0 Successful completion. [EINVAL] The value specified by cond is invalid.

Associated Routines

   pthread_cond_broadcast
   pthread_cond_destroy
   pthread_cond_init
   pthread_cond_timedwait
   pthread_cond_wait