Re^4: Child process inter communication

[marioroy]

Update: Added next statement to not delay unless the inbox is empty.

The following is a demonstration using Parallel::ForkManager + MCE::Shared + Foo::Inbox.

use strict;
use warnings;

use Foo::Inbox;
use Parallel::ForkManager;
use MCE::Shared;

use List::Util 'shuffle';
use Time::HiRes 'sleep';

my $inbox = MCE::Shared->share( Foo::Inbox->new() );
my @names = shuffle qw/ Barny Betty Fred Wilma /;
my $index = 0;

$| = 1;

sub foo {
  my $name  = shift;
  my $count = 0;

  # remove my name from the list
  @names = grep { $_ ne $name } shuffle @names;

  # send greeting to names on the list
  $inbox->send($name, \@names, 'Hello');

  while ( 1 ) {
    if ( my ($from, $data) = $inbox->recv($name) ) {

      # so soon, alrighty then ;-)
      last if $data->[0] eq 'END';

      # display the message received
      printf "%-5s received %s from %s\n", $name, $data->[0], $from;

      # forward the message to another worker
      $inbox->send($name, $names[ ++$index % @names ], $data->[0])
        if ( $from eq 'manager' );

      next;
    }

    sleep 0.01;
  }
}

my $pm = new Parallel::ForkManager(scalar @names);

$pm->set_waitpid_blocking_sleep(0);

foreach my $name ( @names ) {
  $pm->start($name) and next;

  # Have the shared-manager assign a data channel for IPC.
  # This is done automatically for MCE, MCE::Hobo, and threads.
  MCE::Shared->init();

  # Enter the foo routine.
  foo($name);

  $pm->finish($name);
}

# Enter message or type quit to terminate the script.

while ( my $msg = <STDIN> ) {
  chomp $msg; next unless ( length $msg );
  $inbox->end(), last() if ( $msg eq 'quit' );
  $inbox->send('manager', $names[ ++$index % @names ], $msg);
}

$pm->wait_all_children;

MCE::Signal handles signal handling behind the scene if one were to press Ctrl-C (SIGINT). Ditto for the process receiving SIGQUIT or SIGTERM. What is nice about this arrangement is that MCE::Shared and MCE::Signal (loaded by MCE::Shared::Server) complements Parallel::ForkManager quite nice ;-).

For SIGPIPE to work reliably, it requires $| = 1 on STDOUT. Then the following is possible on any Unix platforms. The script terminates gracefully including the tempdir removal inside Parallel::ForkManager.

perl script.pl | head -5

Regards, Mario