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sem_unlink(3) [freebsd man page]

SEM_OPEN(3)						   BSD Library Functions Manual 					       SEM_OPEN(3)

NAME
sem_open, sem_close, sem_unlink -- named semaphore operations LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <semaphore.h> sem_t * sem_open(const char *name, int oflag, ...); int sem_close(sem_t *sem); int sem_unlink(const char *name); DESCRIPTION
The sem_open() function creates or opens the named semaphore specified by name. The returned semaphore may be used in subsequent calls to sem_getvalue(3), sem_wait(3), sem_trywait(3), sem_post(3), and sem_close(). This implementation places strict requirements on the value of name: it must begin with a slash ('/') and contain no other slash characters. The following bits may be set in the oflag argument: O_CREAT Create the semaphore if it does not already exist. The third argument to the call to sem_open() must be of type mode_t and specifies the mode for the semaphore. Only the S_IWUSR, S_IWGRP, and S_IWOTH bits are examined; it is not possible to grant only ``read'' permission on a semaphore. The mode is modified according to the process's file creation mask; see umask(2). The fourth argument must be an unsigned int and specifies the initial value for the semaphore, and must be no greater than SEM_VALUE_MAX. O_EXCL Create the semaphore if it does not exist. If the semaphore already exists, sem_open() will fail. This flag is ignored unless O_CREAT is also specified. The sem_close() function closes a named semaphore that was opened by a call to sem_open(). The sem_unlink() function removes the semaphore named name. Resources allocated to the semaphore are only deallocated when all processes that have the semaphore open close it. RETURN VALUES
If successful, the sem_open() function returns the address of the opened semaphore. If the same name argument is given to multiple calls to sem_open() by the same process without an intervening call to sem_close(), the same address is returned each time. If the semaphore cannot be opened, sem_open() returns SEM_FAILED and the global variable errno is set to indicate the error. The sem_close() and sem_unlink() functions return the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ERRORS
The sem_open() function will fail if: [EACCES] The semaphore exists and the permissions specified by oflag at the time it was created deny access to this process. [EACCES] The semaphore does not exist, but permission to create it is denied. [EEXIST] O_CREAT and O_EXCL are set but the semaphore already exists. [EINTR] The call was interrupted by a signal. [EINVAL] The sem_open() operation is not supported for the given name. [EINVAL] The value argument is greater than SEM_VALUE_MAX. [ENAMETOOLONG] The name argument is too long. [ENFILE] The system limit on semaphores has been reached. [ENOENT] O_CREAT is not set but the named semaphore does not exist. [ENOSPC] There is not enough space to create the semaphore. The sem_close() function will fail if: [EINVAL] The sem argument is not a valid semaphore. The sem_unlink() function will fail if: [EACCES] Permission is denied to unlink the semaphore. [ENAMETOOLONG] The specified name is too long. [ENOENT] The named semaphore does not exist. SEE ALSO
close(2), open(2), umask(2), unlink(2), sem_getvalue(3), sem_post(3), sem_trywait(3), sem_wait(3) STANDARDS
The sem_open(), sem_close(), and sem_unlink() functions conform to ISO/IEC 9945-1:1996 (``POSIX.1''). HISTORY
Support for named semaphores first appeared in FreeBSD 5.0. BSD
January 9, 2010 BSD

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sem_close(3C)						   Standard C Library Functions 					     sem_close(3C)

NAME
sem_close - close a named semaphore SYNOPSIS
#include <semaphore.h> int sem_close(sem_t *sem); DESCRIPTION
The sem_close() function is used to 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(3C)) are undefined. The sem_close() function deallocates (that is, make available for reuse by a subsequent sem_open(3C) 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(3C), then sem_close() has no effect on the state of the semaphore. If the sem_unlink(3C) function has been successfully invoked for name after the most recent call to sem_open(3C) with O_CREAT for this semaphore, then when all processes that have opened the semaphore close it, the semaphore is no longer be accessible. RETURN VALUES
If successful, sem_close() returns 0, otherwise it returns -1 and sets errno to indicate the error. ERRORS
The sem_close() function will fail if: EINVAL The sem argument is not a valid semaphore descriptor. ENOSYS The sem_close() function is not supported by the system. USAGE
The sem_close() function should not be called for an unnamed semaphore initialized by sem_init(3C). ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ |ATTRIBUTE TYPE |ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Committed | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ |Standard |See standards(5). | +-----------------------------+-----------------------------+ SEE ALSO
sem_init(3C), sem_open(3C), sem_unlink(3C), attributes(5), standards(5) NOTES
Solaris 2.6 was the first release to support the Asynchronous Input and Output option. Prior to this release, this function always returned -1 and set errno to ENOSYS. SunOS 5.11 5 Feb 2008 sem_close(3C)

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