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1.4.9.sem_post() #
NAME
sem_post – increment the count of a semaphore
SYNOPSIS
#include <semaphore.h>
- int sem_post(sem_t *sem );
Callable from ISR.
- typedef struct {
- …
- } sem_t /*opaque POSIX semaphore*/
DESCRIPTION
If, prior to the call to sem_post(), the value of sem was 0, and other threads were blocked waiting for the semaphore, then one of them will be allowed to return successfully from its call to sem_wait(). The thread which has been waiting the longest is unblocked.
If, prior to the call to sem_post(), no other threads were blocked for the semaphore, then its value is incremented by one.
RETURN VALUES
If successful, sem_post() returns 0, otherwise it returns -1, and sets errno to indicate the error condition.
ERRORS
- EINVAL
- sem does not refer to a valid semaphore.