sem_open(2) [hpux man page]

sem_open(2)							System Calls Manual						       sem_open(2)

NAME

       sem_open - create/open a named POSIX semaphore

SYNOPSIS


DESCRIPTION

       is  used  to  open  or  create  a named semaphore.  A successful call to will create a descriptor for the semaphore specified by name.  The
       pointer to the semaphore returned by can be used to access the semaphore associated with name in subsequent operations.	The name  argument
       points  to  a string referring to a semaphore. It should begin with a "/" and shall conform to pathname rules except that no path component
       should be "." or "..".

       The oflag argument specifies whether a semaphore is to be created or not.  The following bits in it may be set:

	      If this flag is set, a new semaphore is created if it does not already exist.
			     If this flag is not set, the semaphore should already exist.

	      If this flag is set, the call fails if the semaphore already exists.
			     This flag is valid only when is also set; otherwise, it is ignored.

       The mode and value arguments are provided to supply the permissions and the initial value information necessary for creating  a	new  sema-
       phore.

       To use this function, link in the realtime library by specifying on the compiler or linker command line.

EXAMPLES

       The  following call to will create a new named semaphore if one does not exist, which depends on the flags specified in oflag, has the per-
       missions specified in mode and has an initial value of value.

RETURN VALUE

       If the semaphore was created and initialized, returns a pointer to a structure containing the index of the new descriptor.

       If the semaphore could not be created/initialized, the call returns -1 and sets to indicate the error.  If the named semaphore  is  already
       opened by the calling process, a descriptor and a structure for the named semaphore already exists for the calling process.  A new descrip-
       tor is not created and a pointer to the existing structure is returned for this call.

ERRORS

       fails and does not perform the requested operation if any of the following conditions are encountered:

	      [EACCES]	     The named semaphore exists and the process does not have the permissions to open the semaphore as described by oflag,
			     or the named semaphore does not exist and the process does not have the permission to open it.

	      [EEXIST]	     The flags and are set in oflag and the named semaphore exists.

	      [EINTR]	     A signal interrupted the operation.

	      [EINVAL]	     The argument value is greater than and the flag was specified in oflag.

	      [EINVAL]	     The name argument does not begin with "/" or contains "." or ".." as a pathname component.

	      [EMFILE]	     Too many semaphore descriptors are currently in use by this process.

	      [ENAMETOOLONG] The name string is longer than

	      [ENFILE]	     There are too many semaphores in the system.

	      [ENOENT]	     The flag is not set in oflag and the named semaphore does not exist.

	      [ENOSPC]	     There are insufficient resources for the creation of a new named semaphore.

SEE ALSO

       sem_close(2), sem_post(2), sem_wait(2), sem_unlink(2), privileges(5), <semaphore.h>.

STANDARDS CONFORMANCE

																       sem_open(2)

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