sem_post(3) [freebsd man page]

SEM_POST(3)						   BSD Library Functions Manual 					       SEM_POST(3)

NAME

     sem_post -- increment (unlock) a semaphore

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 indi-
     cate 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 ISO/IEC 9945-1:1996 (``POSIX.1'').

BSD
								 January 28, 2015							       BSD

SEM_POST(3)						     Linux Programmer's Manual						       SEM_POST(3)

NAME

       sem_post - unlock a semaphore

SYNOPSIS

       #include <semaphore.h>

       int sem_post(sem_t *sem);

       Link with -pthread.

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 proceed 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 maximum allowable value for a semaphore would be exceeded.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       +-----------+---------------+---------+
       |Interface  | Attribute	   | Value   |
       +-----------+---------------+---------+
       |sem_post() | Thread safety | MT-Safe |
       +-----------+---------------+---------+
CONFORMING TO

       POSIX.1-2001.

NOTES

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

EXAMPLE

       See sem_wait(3).

SEE ALSO

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

COLOPHON

       This  page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux								    2017-03-13							       SEM_POST(3)