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(3)) are undefined. The
sem_close () function shall deallocate (that is,
make available for reuse by a subsequent sem_open(3) 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(3), then sem_close ()
has no effect on the state of the semaphore. If the
sem_unlink(3) function has been successfully invoked for
name after
the most recent call to sem_open(3) 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 may 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(3), semget(3), semop(3) , sem_init(3), sem_open(3), sem_unlink(3), the Base Definitions volume of IEEE Std 1003.1-2001 (“POSIX.1”), <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 (“POSIX.1”)/Cor 2-2004, item XSH/TC2/D6/113 is applied, updating the ERRORS section so that the [EINVAL] error becomes optional.
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