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sem_open(3)
NAME
  sem_open - Opens/creates a named semaphore for use by a process (P1003.1b)

SYNOPSIS
  #include <semaphore.h>

  sem_t *sem_open (
  const char *name,
  int oflag, ...);

PARAMETERS
  name	  Points to the string naming the semaphore object.

  oflag	  Controls whether the semaphore is created or only accessed by the
	  call to sem_open.  The O_CREAT and O_EXCL flag bits may be set in
	  oflag.

DESCRIPTION
  Use the sem_open function to establish the connection between a named
  semaphore and a process.  Subsequently, the calling process can reference
  the semaphore by using the address returned from the call.  The semaphore
  is available in subsequent calls to sem_wait, sem_trywait, sem_post, and
  sem_getvalue functions.  The semaphore remains usable by the process until
  the semaphore is closed by a successful call to the sem_close function.

  The oflag flag controls whether the semaphore is created or only accessed
  by the call to sem_open.  The O_CREAT and O_EXCL flag bits may be set in
  oflag as follows:

  O_CREAT	 This flag is used to create a semaphore if it does not
		 already exist.	 The O_CREAT argument requires additional
		 arguments:  mode of type mode_t, and value of type unsigned
		 int.  After the semaphore is created, other processes can
		 open the semaphore by calling sem_open with the same value
		 for the name argument.

  The semaphore's user ID is set to the user ID of the process and the
  semaphore's group ID is set to a system default group or to the group ID of
  the process.	The semaphore's permission bits shall be set to the value of
  the mode argument, except for those set in the file mode creation mask of
  the process.

  O_EXCL	 If O_EXCL and O_CREAT are set, sem_open will fail if a
		 semaphore of the same name already exists.

RETURN VALUES
  On successful completion, this function opens the semaphore and returns the
  semaphore's descriptor.  Otherwise, the function returns -1 and sets errno
  to indicate the error.

ERRORS
  The sem_open function fails under the following conditions:

  [EACCES]	      The named semaphore exists and the permissions
		      specified by oflag are denied, or the namedsemaphore
		      does not exist and the permissions specified by oflag
		      are denied.

  [EEXIST]	      O_CREAT and O_EXCL are set and the named semaphore
		      already exists.

  [EINTR]	      The sem_open operation was interrupted by a signal.

  [EINVAL]	      The sem_open operation is not supported for the given
		      name.  Or, O_CREAT was specified in oflag and value wa
		      greater than {SEM_VALUE_MAX}.

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

  [ENAMETOOLONG]      The length of the name string exceeds {PATH_MAX}, or a
		      pathname component is longer than {NAME_MAX} while
		      {_POSIX_NO_TRUNC} is in effect.

  [ENFILE]	      Too many semaphores are currently open in the system.

  [ENOENT]	      O_CREAT is not set and the named semaphore does not
		      exist.

  [ENOSPC]	      There is insufficient space for the creation of the new
		      named semaphore.

RELATED INFORMATION
  Functions: sem_close(3), sem_post(3), sem_trywait(3), sem_unlink(3),
  sem_wait(3)

Index for Section 3

Alphabetical listing for S

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