opensem(S)                     6 January 1993                     opensem(S)


 Name

    opensem - opens a semaphore

 Syntax


    cc ... -lx


    int opensem (sem_name)
    char *sem_name;


 Description

    opensem opens a semaphore named by semname and returns the unique sema-
    phore identification number semnum used by waitsem and sigsem.  creatsem
    should always be called to initialize the semaphore before the first
    attempt to open it.

 System compatibility

    opensem can only be used to open semaphores created under UNIX version
    3.0, not for UNIX System V semaphores.

 Diagnostics

    opensem returns a value of -1 if an error occurs.  If the semaphore named
    does not exist, errno is set to ENOENT.  If the file specified is not a
    semaphore file (i.e., a file previously created by a process using a call
    to creatsem), errno is set to ENOTNAM.  If the semaphore has become
    invalid due to inappropriate use, errno is set to ENAVAIL.

 Notes

    This feature is a XENIX specific enhancement which may not be present in
    all UNIX implementations.


 Warning

    It is not advisable to open the same semaphore more than once.  Although
    it is possible to do this, it may result in a serious deadlock.

 See also

    creatsem(S), sigsem(S), waitsem(S)

 Standards conformance

    opensem is not part of any currently supported standard; it is an exten-
    sion of AT&T System V provided by the Santa Cruz Operation.