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sem_post
<html> <head> <title>sem_post</title> <META NAME="KEYWORDS" CONTENT="sem_post"> </head> <body BGCOLOR="#ffffff" LINK="#0000ff" VLINK="#0000ff" ALINK="#0000ff" TEXT="#000000"> <center> <h1><b>sem_post</b></h1></center> <PRE> <STRONG><A HREF="/man3/SEM_POST">SEM_POST(3)</A></STRONG> Linux Programmer's Manual <STRONG><A HREF="/man3/SEM_POST">SEM_POST(3)</A></STRONG> 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 an- other process or thread blocked in a <STRONG><A HREF="/man3/sem_wait">sem_wait(3)</A></STRONG> 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 er- ror. 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 at- <STRONG><A HREF="/man7/tributes">tributes(7)</A></STRONG>. +-----------+---------------+---------+ |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 sig- nal handler. EXAMPLE See <STRONG><A HREF="/man3/sem_wait">sem_wait(3)</A></STRONG>. SEE ALSO <STRONG><A HREF="/man3/sem_getvalue">sem_getvalue(3)</A></STRONG>, <STRONG><A HREF="/man3/sem_wait">sem_wait(3)</A></STRONG>, <STRONG><A HREF="/man7/sem_overview">sem_overview(7)</A></STRONG>, <STRONG><A HREF="/man7/signal-safety">signal-safety(7)</A></STRONG> COLOPHON This page is part of release 5.05 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 <STRONG><A HREF="/man3/SEM_POST">SEM_POST(3)</A></STRONG></PRE> <center> <h6>Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2025 <a href="http://www.he.net">Hurricane Electric</a>. All Rights Reserved.</h6></center> </body> </html>