NAME

sem_close — close a named semaphore

SYNOPSIS

#include <semaphore.h>

int sem_close(sem_t *sem);


DESCRIPTION

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. If the semaphore indicated by sem is implemented using a file descriptor, the file descriptor shall be closed. 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 all semaphore handles to 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.

ERRORS

The sem_close() function may fail if:

[EINVAL]

The sem argument is not a valid semaphore descriptor.

EXAMPLES

None.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

semctl, semget, semop, sem_init, sem_open, sem_unlink

XBD <semaphore.h>

CHANGE HISTORY

First released in Issue 5. Included for alignment with the POSIX Realtime Extension.

Issue 6

The sem_close() function is marked as part of the Semaphores option.

The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Semaphores option.

IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/113 is applied, updating the ERRORS section so that the [EINVAL] error becomes optional.

Issue 7

The sem_close() function is moved from the Semaphores option to the Base.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0523 [37] is applied.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0317 [870] is applied.

Issue 8

Austin Group Defect 368 is applied, adding a requirement that if sem is implemented using a file descriptor, sem_close() closes the file descriptor.

Austin Group Defect 1324 is applied, clarifying the circumstances under which an unlinked semaphore is no longer accessible.