Hi Anonymous Monk,

Unfortunately, one cannot serialize Imager objects or will crash. This is true for Storable and Sereal::Encoder/Decoder. The thing to do is to save the image into a scalar variable before sending to the manager process.

Testing was done using Ubuntu 18.04.

$ sudo apt update
$ sudo apt install libimager-perl libmce-perl
$ sudo apt install libsereal-encoder-perl libsereal-decoder-perl
$ sudo apt install ttf-mscorefonts-installer

[download]

MCE::Map demonstration

Here is the working parallel demonstration via MCE::Map. 
#!/usr/bin/perl

use strict;
use warnings;
use Imager;
use MCE::Map;

STDOUT->autoflush;

MCE::Map->init(
  max_workers => 6,
  chunk_size  => 1,
  init_relay  => ''
);

my @data = mce_map {
  my $x = $_;
  my $i = Imager->new(xsize=>120, ysize=>50)
  or die  Imager->errstr;
  
  $i->string(
    text  => $x,
    color => Imager::Color->new('ffffff'),
    font  => Imager::Font->new(
      file  => '/usr/share/fonts/truetype/msttcorefonts/cour.ttf',
    # file  => '/System/Library/Fonts/Courier.dfont',
    # face  => 'Courier New', # mswin
      size  => 42,
      aa    => 1),
    x     => 5,
    y     => 35
  );

  # One cannot serialize Imager objects or will crash.
  # Instead save the image to a scalar and send that.
  # The manager process later reads from scalar refs.

  $i->write(data => \my $data, type => 'gif');

  MCE::relay { print "\r$x" };

  $data;
  
} [ 0 .. 9999 ];

MCE::Map->finish;

Imager->write_multi({
  file => 'gif.gif', type => 'gif', gif_loop => 0, gif_delay => 1
}, map { Imager->read_multi(data => \$_) } @data) or die Imager->errst
+r;

print " frame GIF done!\n";

[download]

MCE::Loop demonstration

Here is another way using MCE::Loop. I call MCE gather inside the relay block. 
#!/usr/bin/perl

use strict;
use warnings;
use Imager;
use MCE::Loop;

STDOUT->autoflush;

my @data;

MCE::Loop->init(
  max_workers => 6,
  chunk_size  => 1,
  init_relay  => '',
  gather      => sub {
    push @data, $_[1];
    print "\r$_[0]";
  }
);

mce_loop {
  my $x = $_;
  my $i = Imager->new(xsize=>120, ysize=>50)
  or die  Imager->errstr;
  
  $i->string(
    text  => $x,
    color => Imager::Color->new('ffffff'),
    font  => Imager::Font->new(
      file  => '/usr/share/fonts/truetype/msttcorefonts/cour.ttf',
    # file  => '/System/Library/Fonts/Courier.dfont',
    # face  => 'Courier New', # mswin
      size  => 42,
      aa    => 1),
    x     => 5,
    y     => 35
  );

  # One cannot serialize Imager objects or will crash.
  # Instead save the image to a scalar and send that.
  # The manager process later reads from scalar refs.

  $i->write(data => \my $data, type => 'gif');

  MCE::relay { MCE->gather($x, $data) };

} [ 0 .. 9999 ];

MCE::Loop->finish;

Imager->write_multi({
  file => 'gif.gif', type => 'gif', gif_loop => 0, gif_delay => 1
}, map { Imager->read_multi(data => \$_) } @data) or die Imager->errst
+r;

print " frame GIF done!\n";

[download]

Chunking demonstration for HEDT systems

Reducing IPC overhead (i.e. relay) is possible simply by chunking. 
#!/usr/bin/perl

use strict;
use warnings;
use Imager;
use MCE::Loop;

STDOUT->autoflush;

my $count = 0;
my @data;

MCE::Loop->init(
  max_workers => MCE::Util::get_ncpu(),
  chunk_size  => 100,
  init_relay  => '',
  gather      => sub {
    if (@_ == 1) {
      print "\r", $count++;
    } else {
      push @data, @{ $_[1] };
    }
  }
);

mce_loop {
  my ($mce, $chunk_ref, $chunk_id) = @_;
  my @i_data;

  for my $x (@{ $chunk_ref }) {
    my $i = Imager->new(xsize=>120, ysize=>50)
    or die  Imager->errstr;
  
    $i->string(
      text  => $x,
      color => Imager::Color->new('ffffff'),
      font  => Imager::Font->new(
        file  => '/usr/share/fonts/truetype/msttcorefonts/cour.ttf',
      # file  => '/System/Library/Fonts/Courier.dfont',
      # face  => 'Courier New', # mswin
        size  => 42,
        aa    => 1),
      x     => 5,
      y     => 35
    );

    # One cannot serialize Imager objects or will crash.
    # Instead save the image to a scalar and send that.
    # The manager process later reads from scalar refs.

    $i->write(data => \my $data, type => 'gif');
    push @i_data, $data;

    MCE->gather($x);
  }

  MCE::relay { MCE->gather($chunk_id, \@i_data) };

} [ 0 .. 9999 ];

MCE::Loop->finish;

Imager->write_multi({
  file => 'gif.gif', type => 'gif', gif_loop => 0, gif_delay => 1
}, map { Imager->read_multi(data => \$_) } @data) or die Imager->errst
+r;

print " frame GIF done!\n";

[download]

This has been rather interesting. There is an overall speedup, but not what I expected. Well, here are the various ways to run parallel. One may call gather multiple times inside a MCE code block. However, MCE::relay must be one time only. Not more or less.

Regards, Mario

In reply to Re: MCE segmentation fault by marioroy
in thread MCE segmentation fault by Anonymous Monk

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