Opens/creates a named semaphore for use by a process.

    This function is supported on OpenVMS Integrity servers and
    Alpha only.

    Format

      #include  <semaphore.h>

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

1  –  Argument

 name

    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

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

 value

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

2  –  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.

3  –  Return Values

    sem                Successful completion. The function opens
                       the semaphore and returns the semaphore's
                       descriptor.
    sem_failed         Indicates an error. The function sets errno to
                       one of the following values:

                       o  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.

                       o  EEXIST-O_CREAT and O_EXCL are set, and the
                          named semaphore already exists.

                       o  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}.

                       o  EMFILE-Too many semaphore descriptors or
                          file descriptors are currently in use by
                          this process.

                       o  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.

                       o  ENFILE-Too many semaphores are currently
                          open in the system. ENOENT O_CREAT is
                          not set, and the named semaphore does not
                          exist.

                       o  ENOSPC-Insufficient space exists for the
                          creation of a new named semaphore.

                       o  EVMSERR-OpenVMS specific nontranslatable
                          error code.