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Manual Pages  — SEM_POST

NAME

sem_post – increment (unlock) a semaphore

CONTENTS

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <semaphore.h>

int
sem_post(sem_t *sem);

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().

The sem_post() function is signal-reentrant and may be called within signal handlers.

RETURN VALUES

The sem_post function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

ERRORS

The sem_post() function will fail if:
[EINVAL]
  The sem argument points to an invalid semaphore.
[EOVERFLOW]
  The semaphore value would exceed SEM_VALUE_MAX.

SEE ALSO

sem_getvalue(3), sem_trywait(3), sem_wait(3)

STANDARDS

The sem_post() function conforms to IEEE Std 1003.1-96 ("POSIX.1").

SEM_POST (3) January 28, 2015

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