Re^4: Please Explain the Parallel::ForkManager Idiom my $pid = $pm->start and next;

[Jim]

Why?

Exactly! That's the code in the demo script in the Parallel::ForkManager documentation. It's the example I was running and studying earlier. The PIDs and exit codes are included in the code for didactic reasons.

You'll appreciate my similar demo script based on the same kids-in-line-at-the-pool theme.

use strict;
use warnings;

use Parallel::ForkManager;

$| = 1;

my $MAXIMUM_KIDS_IN_POOL =  3;
my $MAXIMUM_TIME_IN_POOL = 30; # Seconds

my $lifeguard = Parallel::ForkManager->new($MAXIMUM_KIDS_IN_POOL);

my @kids = qw( Ann Bob Cal Dan Eve Fay Gus Hal Ike Joe Kim Lee Meg );

$lifeguard->run_on_start(
    sub {
        my ($pid, $kid) = @_;
        print "\nThe lifeguard waves $kid into the pool\n";
    }
);

$lifeguard->run_on_finish(
    sub {
        my ($pid, $exit_code, $kid) = @_;
        print "\n$kid climbs out of the pool\n";
    }
);

$lifeguard->run_on_wait(
    sub {
       print ".";
    }, 0.3
);

my $number_of_kids = @kids;

print "\nThere are $number_of_kids kids in line at the pool\n\n@kids\n
+";

KID_IN_LINE:
for my $kid (@kids) {
    my $pid = $lifeguard->start($kid);

    next KID_IN_LINE if $pid != 0;

    srand();

    my $time = int(rand($MAXIMUM_TIME_IN_POOL)) + 1;

    print "\n$kid jumps into the pool\n";

    sleep $time;

    print "\nThe lifeguard orders $kid out of the pool after $time sec
+onds\n";

    sleep 0.5;

    $lifeguard->finish();
}

print "\nAll the kids have been in the pool\n";

$lifeguard->wait_all_children();

print "\nAll the kids are out of the pool\n";

exit 0;

(As I post this script here, I notice there are vestiges of the original script still in the callback subs; namely, $pid and $exit_code. I could remove them.)

Jim

UPDATE:  And if I'm truly serious about not caring about the PIDs, I could do this instead:

    next KID_IN_LINE if $lifeguard->start($kid) != 0;

ANOTHER UPDATE:  More weirdness. This works fine…

$lifeguard->run_on_start(
    sub {
        my $kid = pop;
        print "\nThe lifeguard waves $kid into the pool\n";
    }
);

…but this blows up with Use of uninitialized value $kid in concatenation (.) or string at Pool.pl line 27…

$lifeguard->run_on_finish(
    sub {
        my $kid = pop;
        print "\n$kid climbs out of the pool\n";
    }
);

No variation of pop()-ing @_ in run_on_finish() works.

YET ANOTHER UPDATE:  OK, this is documented in…ahem…the documentation.