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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