I have been looking at utilizing Parallel::ForkManager in a project where I work, but I have run into a question for which I hope someone may be able to shed some light, or suggest a solution.

The project I am working on involves a process which processes information regarding a large number of devices, which means it may take several hours to collect and process all the information being used. I am looking at using P::FM as a way of handling a number of these concurrently to reduce the running time.

Because of the processing involved, however, there is a limited window of time in which the process may run without impacting other systems. Looking through the Perl Cookbook, I found example 16.21, referring to the use of eval() and signals, and thought perhaps I could combine the approaches. This is where my experience fails me as to what to expect.

Below is a snippet (haven't started writing the actual code) to give an idea of what I am thinking, but I want to confirm that there will be no weirdness that is immediately apparent, and that I am on the right track with the idea. Does this seem reasonable? Is there a better way? Is my understanding of what will happen with set_max_procs(0) correct?

Let me express my appreciation for any comments and assistance in advance. 

#!/usr/bin/perl -w
#
# Sample snipped, containing code taken from the 
# documentation for Parallel::ForkManager and 
# example 16.21 from the _Perl_Cookbook_.
#
use strict;
use vars qw($pm);
use Parallel::ForkManager;

#
# Maximum of 20 simultaneous processes,
# and begin graceful shutdown after 6 hrs.
#
my $MAX_PROCESSES = 20;
my $MAX_TIME = 6 * 3600;

$pm = new Parallel::ForkManager($MAX_PROCESSES) 
or die("Unable to create ForkManager object: $!\n");

#
# &load_data() subroutine defined elsewhere
#
my (@all_data);
@all_data = &load_data();

$SIG{ARLM} = sub { die("TimeOut"); };
eval {
    alarm($MAX_TIME);
    foreach my $data (@all_data) {
        my $pid = $pm->start and next;

        # Process or call processing routines 
        # for $data here

        $pm->finish;
    }
    $pm->wait_all_children;
    alarm(0);
};
if ($@) {
    if ($@ =~ m/TimeOut/) {
        $pm->set_max_procs(0);
        $pm->wait_all_children;
    }
    else {
        alarm(0);
        die;
    }
}

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In reply to Graceful shutdowns and Parallel::ForkManager by atcroft

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