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NetBSD 6.1.5 - man page for sem_unlink (netbsd section 3)

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

NAME
     sem_open, sem_close, sem_unlink -- named semaphore operations

LIBRARY
     POSIX Real-time Library (librt, -lrt)

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().

     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 exam-
	      ined; 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 sem-
     aphore 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 and 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), sem(4)

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 NetBSD 2.0.

BUGS
     This implementation places strict requirements on the value of name: it must begin with a
     slash ('/'), contain no other slash characters, and be less than 14 characters in length not
     including the terminating null character.

BSD					 January 21, 2005				      BSD
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