Hello 1nickt,

The gather option must be set each time when running MCE inside a loop. In that case, it's easier to use MCE::Flow instead which allows one to pass a hash containing MCE options for the job.

use strict; use warnings; use feature 'say';
use Data::Dumper; ++$Data::Dumper::Sortkeys;

use MCE::Flow;
use MCE::Candy;

my $aref = [];

MCE::Flow::init(
    max_workers => 4,
    chunk_size  => 1,
);

for ( 0, 1 ) {
    say "Test $_";
    mce_flow {
        gather => MCE::Candy::out_iter_array( $aref )
    },
    sub {
        my ( $mce, $chunk_ref, $chunk_id ) = @_;
      # warn "chunk_ref " . Dumper $chunk_ref;
        my ($chunk) = @{ $chunk_ref };
      # warn "chunk " . Dumper $chunk;

        MCE->gather( $chunk_id, $chunk->{'foo'} );
    },
    get_data( $_ );

    say "$_ : " . Dumper $aref;
    $aref = [];
}

sub get_data {
    my $which = shift;
    if ( $which == 1 ) {
        return [
            { foo => 'bar', baz => 'qux' }
        ];
    } else {
        return [
            { foo => 'bar', baz => 'qux' },
            { foo => 'qux', baz => 'bar' },
        ];
    }
}
[download]

Output

Test 0
0 : $VAR1 = [
          'bar',
          'qux'
        ];

Test 1
1 : $VAR1 = [
          'bar'
        ];
[download]

Regards, Mario.

Update:

When gathering data and running inside a loop, it's important to specify the gather option each time. MCE::Candy::out_iter_array($aref) returns a closure block contaning a lexical order_id variable starting at 1. Basically, order_id correlates to chunk_id. Out of order items are held temporarily.

sub out_iter_array {

   my $_aref = shift; my %_tmp; my $_order_id = 1;

   _croak("The argument to \"out_iter_array\" is not an array ref.")
      unless ( ref $_aref eq 'ARRAY' );

   return sub {
      my $_chunk_id = shift;

      if ( $_chunk_id == $_order_id && keys %_tmp == 0 ) {
         # already orderly
         $_order_id++; push @{ $_aref }, @_;
      }
      else {
         # hold temporarily otherwise until orderly
         @{ $_tmp{ $_chunk_id } } = @_;

         while ( 1 ) {
            last unless exists $_tmp{ $_order_id };
            push @{ $_aref }, @{ delete $_tmp{ $_order_id++ } };
         }
      }
   };
}
[download]