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SEM_POST

Section: Linux Programmer's Manual (3)
Updated: 2009-03-30
Index Return to Main Contents

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NAME

sem_post - unlock a semaphore  

SYNOPSIS

#include <semaphore.h>

int sem_post(sem_t *sem);

Link with -lrt or -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.

 

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)  

COLOPHON

This page is part of release 3.35 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://man7.org/linux/man-pages/.

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Index

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

CONFORMING TO

NOTES

EXAMPLE

SEE ALSO

COLOPHON

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