Very Computer

We cannot  trust pid numbers in Unix ,  because they are reused.

Is there a safe way to see if a process is alive from another process ?

We have a application that uses shared library for the API processes.
If we restart our main application we need to know if there is any
API processes out there. We need to map them in to our global memory
region
again after we have restarted the main application.

We have been thinking about locking but can't really see how to check
locks from different processes (pthread_mutex_lock).

Is there some system wide locking in UNIX ??
I'm a VMS person so i don't know that much about UNIX , but i know there

is system and cluster wide locking in VMS !

Maybe one solution is to set a file lock , but rather avoid that !

Regards

Stig Simonsson

Quote:>Maybe one solution is to set a file lock , but rather avoid that !

Too bad, that's what I was going to suggest.

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System V style IPC provides semaphores accessible between processes.  I
haven't ever had occasion to use this and so I don't know the details,
but it might be worth investigating.
--

Nate Eldredge

Apart from file-locking and inter-process semaphores,

there is another way to do this.

Use a pre-assigned unix port. When your application

starts-up, it can find out whether the port is already

in use. The advantage of this method is that you can

also exchange information during startup using the port.

-Sameer

http://www.cs.arizona.edu/~samverk

You obviously didn't read the first sentence of his message.  Since PIDs
can be reused, this won't tell you if it's the process you care about, it
could be some unrelated process that happened to get the same PID.

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More like:

        if (kill(pid, 0) == 0 || errno != ESRCH) {
            /* alive */
        }
--
Expressed in this posting are my opinions.  They are in no way related
to opinions held by my employer, Sun Microsystems.
Statements on Sun products included here are not gospel and may
be fiction rather than truth.

System V semaphores could be useful because of the AOE (adjust on exit)
feature.  Using the SEM_UNDO flag with a sem_op means the kernel will
essentially 'undo' the sem_op if the process that performed the sem_op
dies.  For more info, see Advanced Programming in the UNIX Environment
(W.R. Stevens).