First thing I thought of was shared memory. In IPC::Shareable, if one attempts to create a shared memory segment that has already been created in a separate process with exclusive set, the second process will croak(). So what I did is add a graceful flag to its options, and when set, the second process that tries to create the exclusive segment simply exits gracefully with no noise or anything. Observe:

lock.pl:

use warnings;
use strict;

use IPC::Shareable;

tie my $lock, 'IPC::Shareable', {
    key         => 'LOCK',
    create      => 1,
    exclusive   => 1,
    destroy     => 1,
    graceful    => 1
};

$lock = $$;
print "procID: $lock\n";

sleep 5;

[download]

Run it in one window:

spek@scelia ~/scratch $ perl lock.pl
procID: 21241

[download]

...it sleeps for a few seconds, during which we run it in the second window:

spek@scelia ~/repos/ipc-shareable $ perl ~/scratch/lock.pl
spek@scelia ~/repos/ipc-shareable $

[download]

...it exited before it printed anything. After the five second sleep in proc one is done, run it in window two:

spek@scelia ~/repos/ipc-shareable $ perl ~/scratch/lock.pl
procID: 21339

[download]

So, in essence, this question prompted me to update the distribution to handle your very issue, ummm, well, gracefully. I just published it, so it may not yet be available at your mirror. Version 1.01 has the new 'graceful' feature.

In reply to Re: singleton lock not reliable by stevieb
in thread singleton lock not reliable by pidloop

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