sem_close - Man Page

close a named semaphore


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <semaphore.h>

int sem_close(sem_t *sem);


The sem_close() function shall indicate that the calling process is finished using the named semaphore indicated by sem. The effects of calling sem_close() for an unnamed semaphore (one created by sem_init()) are undefined. The sem_close() function shall deallocate (that is, make available for reuse by a subsequent sem_open() by this process) any system resources allocated by the system for use by this process for this semaphore. The effect of subsequent use of the semaphore indicated by sem by this process is undefined. If any threads in the calling process are currently blocked on the semaphore, the behavior is undefined. If the semaphore has not been removed with a successful call to sem_unlink(), then sem_close() has no effect on the state of the semaphore. If the sem_unlink() function has been successfully invoked for name after the most recent call to sem_open() with O_CREAT for this semaphore, then when all processes that have opened the semaphore close it, the semaphore is no longer accessible.

Return Value

Upon successful completion, a value of zero shall be returned. Otherwise, a value of -1 shall be returned and errno set to indicate the error.


The sem_close() function may fail if:


The sem argument is not a valid semaphore descriptor.

The following sections are informative.



Application Usage




Future Directions


See Also

semctl(), semget(), semop(), sem_init(), sem_open(), sem_unlink()

The Base Definitions volume of POSIX.1-2017, <semaphore.h>

Referenced By

_Exit(3p), semaphore.h(0p), semctl(3p), semget(3p), semop(3p), sem_open(3p), sem_unlink(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual