UpTide, welcome to the monastery.

The following is a modification by BrowserUk's demonstration. Task A, B, C are spawned with 1, 2, 3 workers respectively. If threads is desired, load threads before MCE. By default, MCE spawns child processes on UNIX and Cygwin.

#!/usr/bin/perl

use strict;
use warnings;

use threads;
use Thread::Queue;

sub task_a {
    my ($Qb, $Qc) = @_;
    for (1 .. 1e5) {
        $Qb->enqueue(1e3 + int(rand 1000));
        $Qc->enqueue(2e3 + int(rand 1000));
    }
    $Qb->enqueue(undef) for 1 .. 2;
}

sub task_b {
    my ($Qb, $Qc) = @_;
    while ( my $arg1 = $Qb->dequeue() ) {
        $Qc->enqueue($arg1 * 10);
    }
    $Qc->enqueue(undef) for 1 .. 3;
}

sub task_c {
    my ($Qc) = @_;
    while ( my $arg1 = $Qc->dequeue() ) {
        print "$arg1\n";
    }
}

my $Qb = new Thread::Queue;
my $Qc = new Thread::Queue;
my @thrs;

push @thrs, threads->new( \&task_a, $Qb, $Qc ) for 1 .. 1;
push @thrs, threads->new( \&task_b, $Qb, $Qc ) for 1 .. 2;
push @thrs, threads->new( \&task_c, $Qc      ) for 1 .. 3;

$_->join for @thrs;

print "Done\n";
[download]

The following does the same thing using the MCE module. The await method prevents the queue from exceeding 200 items.

#!/usr/bin/perl

use strict;
use warnings;

use MCE::Step;

sub task_a {
   for (1 .. 1e5) {
      MCE->await('B', 200) if $_ % 200 == 0;
      MCE->enq('B', 1e3 + int(rand 1000));

      MCE->await('C', 200) if $_ % 200 == 0;
      MCE->enq('C', 2e3 + int(rand 1000));
   }
}

sub task_b {
    my ($mce, $arg1, $arg2, $argN) = @_;
    MCE->enq('C', $arg1 * 10);
}

sub task_c {
    my ($mce, $arg1, $arg2, $argN) = @_;
    print "$arg1\n";
}

MCE::Step->init(
   task_name   => [ 'A', 'B', 'C' ],
   max_workers => [  1,   2,   3  ],
);

mce_step \&task_a, \&task_b, \&task_c;

print "Done\n";
[download]

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