sem_post

Name

sem_post
- increment (unlock) a semaphore

Library

libpthread.lib

Synopsis

#include <semaphore.h>

int sem_post (sem_t *sem);

Return values

If successful, function shall return zero; otherwise, the function shall return -1 and set errno to indicate the error.

Detailed description

The sem_post function increments (unlocks) the semaphore pointed to by sem. If there are threads blocked on the semaphore when sem_post is called, then the highest priority thread that has been blocked the longest on the semaphore will be allowed to return from sem_wait.

Examples

sem_t psem;   
if (sem_init(&psem, 0, 1) < 0) {
        perror("sem_init");
        return -1;
   }
if( sem_post(psem) == -1 ) {
  perror( "sem_post failed");
  return -1;
 }

Errors

The sem_post function will fail if:

[`EINVAL`]
	The sem argument points to an invalid or uninitialized semaphore.

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