SEM_POST

Section: Linux Programmer's Manual (3)
Updated: 2017-03-13
Index Return to Main Contents

---

 

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 4.13 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/.

---

 

Index

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

ATTRIBUTES

CONFORMING TO

NOTES

EXAMPLE

SEE ALSO

COLOPHON