File locking is hard to do right but possible, and can be used to ensure your process doesn't collide with another instance of itself.

There will certainly be caveats under Windows, some of which might be enumerated in perlport.

I think there is some lock modules on cpan that simplify/abstract the complexity

Hi Dave,

What if I can manage that same script does not runs in parallel will perl scritps accessing separate excel files can also cause any issue?? I also used Win32::OLE module for many scripts.

So you now are ok with the same script running as long as it's acting on different files? Then yes, that's just fine. Use flock, as discussed in the slides I linked to, to lock the files you are acting upon. That will ensure that multiple instances of your script cannot possibly touch the same file. If you do that, sure, there's nothing wrong with running the same script multiple times simultaneously against different data sets, so long as none of the instances attempt to write to the same file.




Dave

To prevent multiple instances of the same script from running, I found it very beneficial to (try to) lock $0.

This approach will fail for symlinks and hardlinks maybe.

That's a good point Corion regarding locking $0. I updated the code by not appending the suffix ".lock" when path is given. The lock is released automatically upon termination of the script.

use Mutex::Flock;

( my $mutex = Mutex::Flock->new( path => $0 ) )->lock_exclusive;

...
[download]

Another way, with the timewait method.

my $mutex = MCE::Mutex::Flock->new( path => $0 );

# terminate script if a previous instance is still running
exit unless $mutex->timedwait(2);

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[download]

The module is beneficial regarding supporting threads and processes. I will make time to complete it and subsequently a release for CPAN.

Regards, Mario

Edit: Added timedwait example.

Greetings 9mohit2,

I put together a Fcntl-based (flock) advisory locking module posted here. Any Perl toolbox might want this.

I'm sorry, but lack the time making modules for CPAN. This is my contribution to the Perl community. Thanks all. I love PerlMonks and enjoyed posting solutions from time to time.

Regards, Mario

Greetings.

The project is completed including a release on CPAN. To ensure a given script is executing once, the following is how to do it using Mutex. That will block until obtaining an exclusive lock. A false value is returned if the timeout is reached, and a true value otherwise.

use Mutex;

my $mutex = Mutex->new( path => $0 );

# terminate script if a previous instance is still running
exit unless $mutex->timedwait( 2 );

...
[download]

Regards, Mario

Edit: Updated the CPAN link to point to the 1.001 release.

Have you considered using a job queue something like Queue::DBI perhaps ?.