opensem(S)
opensem --
opens a semaphore
Syntax
cc ... -lx
int opensem (sem_name)
char *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 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 extension of AT&T System V provided by the Santa Cruz Operation.
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003