sem_post(3)		    Library Functions Manual		     sem_post(3)

NAME
     sem_post - unlock a semaphore

LIBRARY
     POSIX threads library (libpthread, -lpthread)

SYNOPSIS
     #include <semaphore.h>

     int sem_post(sem_t *sem);

DESCRIPTION
     sem_post()	 increments  (unlocks)	the semaphore pointed to by sem.  If the
     semaphore's value consequently becomes  greater  than  zero,  then	 another
     process  or  thread blocked in a sem_wait(3) call will be woken up and pro-
     ceed to lock the semaphore.

RETURN VALUE
     sem_post() returns 0 on success; on error, the value of  the  semaphore  is
     left unchanged, -1 is returned, and errno is set to indicate the error.

ERRORS
     EINVAL
	    sem is not a valid semaphore.

     EOVERFLOW
	    The value would exceed SEM_VALUE_MAX.

ATTRIBUTES
     For  an  explanation  of the terms used in this section, see attributes(7).
     allbox; lbx lb lb l l l.  Interface Attribute Value T{ sem_post()
     T}	  Thread safety	  MT-Safe

STANDARDS
     POSIX.1-2008.

HISTORY
     POSIX.1-2001.

NOTES
     sem_post() is async-signal-safe: it may be safely called  within  a  signal
     handler.

EXAMPLES
     See sem_wait(3) and shm_open(3).

SEE ALSO
     sem_getvalue(3), sem_wait(3), sem_overview(7), signal-safety(7)

Linux man-pages 6.18		   2026-02-08			     sem_post(3)