NAME

sem_close - close a named semaphore (REALTIME)

SYNOPSIS

[SEM] #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. The effect of subsequent use of the semaphore indicated by sem by this process 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.

ERRORS

The sem_close() function shall fail if:

[EINVAL]

The sem argument is not a valid semaphore descriptor.

EXAMPLES

None.

APPLICATION USAGE

The sem_close() function is part of the Semaphores option and need not be available on all implementations.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

semctl() , semget() , semop() , sem_init() , sem_open() , sem_unlink() , the Base Definitions volume of IEEE Std 1003.1-2001, <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.