Name

sem_post — unlock a semaphore

Synopsis

        #include <semaphore.h>
int sem_post( sem_t *sem);
 
[Note] Note

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 4.12 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/.


  t
Copyright (C) 2006 Michael Kerrisk <mtk.manpagesgmail.com>

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