sem_close.2 (2010 09)

sem_close(2) sem_close(2)

NAME

sem_close - close a named POSIX semaphore

SYNOPSIS

#include <sys/semaphore.h>

int sem_close(sem_t *sem);

DESCRIPTION

sem_close() is used to close a named semaphore. A successful call to

sem_close() will do the fol-

lowing: Remove the process’s descriptor for the semaphore referenced by the speciﬁed

sem_t structure

sem . Remove the semaphore referenced by the speciﬁed

sem_t structure sem , if the semaphore is

marked for removal by a call to

sem_unlink()

and there are no other descriptors referencing this

semaphore.

When the process’s descriptor for the semaphore referenced by sem is removed, subsequent use of this

semaphore by this process will fail. Descriptors for named semaphores are also removed by processes on

exit. Calling

sem_close() does not affect other processes referencing the same semaphore.

To use this function, link in the realtime library by specifying

-lrt on the compiler or linker command

line.

EXAMPLES

The following call to

sem_close() will close a named semaphore referred to by sem by removing the

process’s descriptor to the semaphore and removing the semaphore if it is marked for removal by a previ-

ous sem_unlink() and there are no descriptors referencing it.

sem_close(sem);

RETURN VALUE

If the semaphore was closed and the descriptors referencing it were removed, sem_close() returns 0 to

the caller.

If the semaphore could not be closed, the call returns -1 and sets

errno to indicate the error.

ERRORS

sem_close() fails and does not perform the requested operation if the following condition is encoun-

tered:

[EINVAL] The argument sem is not a valid named semaphore.

WARNINGS

A single sem_close() call will make the semaphore unusable by the process no matter how many

times that process had called sem_open() for the same semaphore. Subsequent calls to sem_close()

by the same process for the same semaphore will result in an undeﬁned behavior.