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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 ooption,
  mode_t mode,
  unsigned int value);

LIBRARY
  Realtime Library (librt.so, librt.a)

PARAMETERS
  name
      Points to a string naming the semaphore object.

  ooption
      Specifies whether the semaphore is to be created (O_CREAT option bit
      set) or only opened (O_CREAT option bit clear).  If O_CREAT is set, the
      O_EXCL option bit may additionally be set to specify that the call
      should fail if a semaphore of the same name already exists.  The
      O_CREAT and O_EXCL options are defined in the <fcntl.h> header file.

  mode
      Specifies the semaphore's permission bits. This argument is used only
      when the semaphore is being created.

  value
      Specifies the initial value to be given to the semaphore. This argument
      is used only when the semaphore is being created.

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 O_CREAT option bit in the ooption parameter controls whether the
  semaphore is created or only opened by the call to sem_open.

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

  After a semaphore is created, other processes can open the semaphore by
  calling sem_open with the same value for the name argument.

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 ooption are
      denied, or the named semaphore does not exist and the permissions
      specified by ooption 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 ooption and value was 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]
      Insufficient space exists for the creation of a new named semaphore.

SEE ALSO
  Functions: sem_close(3), sem_post(3), sem_trywait(3), sem_unlink(3),
  sem_wait(3), mkfifo(3)

  Guide to Realtime Programming

Index for Section 3

Alphabetical listing for S

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