OPENSEM(S)               XENIX System V                OPENSEM(S)



     Name
          opensem - Opens a semaphore.

     Syntax
          int opensem(sem_name)
          char *sem_name;

          sem_num = opensem(sem_name);

     Description
          opensem opens a semaphore named by sem_name and returns the
          unique semaphore identification number sem_num 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
          version 3.0, not for  System V semaphores.

     See Also
          creatsem(S), sigsem(S), waitsem(S)

     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.  This function must
          be linked with the linker option -lx.

     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.















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