opensem(2)                SYSTEM CALLS                 opensem(2)



NAME
     opensem - opens a semaphore

SYNOPSIS
     cc [flag ...] file ... -lx
     int opensem(int semname, char *semnum);

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.

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.

SEE ALSO
     creatsem(2), sigsem(2), waitsem(2).

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.


























            Last change: XENIX Compatibility Package            1