5

How do I share the hash reference $ref across main thread and worker threads ?

#!/usr/bin/perl
use strict;
use warnings;

use threads;
use threads::shared;

my $ref = {};
$ref->{0}->{abc} = 123;
$ref->{1}->{abc} = 223;

printf( "%d\n", $ref->{0}->{abc} );
printf( "%d\n", $ref->{1}->{abc} );

issue_all_jobs($ref);

while (1)
{
    printf( "%d\n", $ref->{0}->{abc} );
    printf( "%d\n", $ref->{1}->{abc} );
    sleep(1);
}

sub issue_all_jobs
{
    my ($ref) = @_;
    for ( my $i = 0; $i < 2; $i++ )
    {
        $ref->{$i}->{handle} = new threads( \&issue_job, $ref, $i );
        $ref->{$i}->{handle}->detach();
    }
}

sub issue_job
{
    my ( $ref, $i ) = @_;
    $ref->{$i}->{abc} = 555123 + $i;
    sleep(2);
}
Jean
  • 21,665
  • 24
  • 69
  • 119

1 Answers1

5

This doesn't work as well as you might think. One of the limitations of threads::shared is that it works fine for sharing single dimensional containers, but it gets rather messy when trying to work on nested data structures, because the compiler doesn't 'know' what it needs to share.

http://perldoc.perl.org/threads/shared.html#BUGS-AND-LIMITATIONS

So - for starters - you need to designate your shared variables as shared in the first place. Either at declaration:

my $ref : shared;

But as you're trying to share a hash 

shared_clone ( $ref );

But personally - I'd shy away from such things. I dislike using shared memory objects, and would generally prefer to use Thread::Semaphore and Thread::Queue and pass data back and forth in a queue. Storable helps a great deal with this, as you can freeze and thaw a data object for insertion into a queue.

Sobrique
  • 52,974
  • 7
  • 60
  • 101
  • Thank you for continuing to bring your threading expertise to SO. I appreciate your contributions. – Miller Oct 28 '14 at 21:27
  • 3
    Major reason I started learning threading/forking - and for that matter, OO - is because it makes all the people I know who are on a high horse about how 'perl is inferior' look a bit sick when I suggest it. – Sobrique Oct 29 '14 at 07:31