Am using Parallel::ForkManager using ActiveState Perl 5.10.1 (1006) on Vista Home Premium SP1 and have been getting something rather strange happen.

When initiated in "debug"

my $pm = new Parallel::ForkManager(0);

the code runs in about 11 seconds to run - but if I tell it to run any number of instances (including 1)

my $pm = new Parallel::ForkManager(1); my $pm = new Parallel::ForkManager(5);

then the run time INCREASES ("1" takes seconds and "5" takes many hours to run) rather than the expected decrease (given that I'm running the code on a quad core system doing naff all otherwise ... and the Windows Performance Monitor suggests that the other cores come alive as expected).

Which suggests that I'm doing summat odd - but I've tried to implement code that is based on reference model provided in the ForkManager documentation. 


sub scoring {
    return 1;
}

my @results = ();
$pm->run_on_finish(
    sub {
                my ($pid, $exit_code, $ident ) = @_;
                $results[$ident] = $exit_code;
            }
);

for ( my $i = 0; $i < 1000000; $i++ ) {
    my $pid = $pm->start($i) and next;
    my $result = scoring();
    $pm->finish($result);
}
$pm->wait_all_children;

[download]

This is cut down PoC code - the real version does much more processing in the child, but the runtime issue is the same... massively increased run-time when actually forking.

Any ideas ?

In reply to ForkManager Running Real Slow by zacc

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