pheller has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I use both Parallel::ForkManager and File::Where in a large project. For some reason, it seems that where_pm can only be called from the first child process, and this also seems system dependent.

An example to illustrate the problem:

#!perl

use Parallel::ForkManager;
use File::Where qw(where_pm);
use strict;
use warnings;

my $pm = new Parallel::ForkManager(2);
for my $i (1 .. 3) {
  my $pid = $pm->start and next;

  my @ret = File::Where->where_pm("File::Where");
  print $ret[1]."\n";
  $pm->finish;
}
$pm->wait_all_children;

[download]

And, example output:
[pheller@lunatic:~/Source/test]% perl ./test.pl
/Library/Perl/5.8.6
Undefined subroutine File::Where::where_pm at ./test.pl line 12
Undefined subroutine File::Where::where_pm at ./test.pl line 12

[download]
Any thoughts?

Replies are listed 'Best First'.
Re: File::Where->where_pm failure in forked children?
by ikegami (Patriarch) on Mar 15, 2007 at 01:19 UTC

    File::Where relies on DATA. I bet the file pointer is shared among the child processes.

    Sorry, I must run, so I can't verify my guess or come up with a solution right now. But hopefully, it will put you on the right path.

[reply]
[d/l]
      Good call. I created a local copy of Where.pm, removed the SelfLoader bits and the example code runs without fail.

      Any ideas how to solve this, short of creating a modified version of File::Where?
[reply]
        Ok, I figured out a solution myself :-)
        #!perl

use Parallel::ForkManager;
use strict;
use warnings;

my $pm = new Parallel::ForkManager(2);
for my $i (1 .. 3) {
  my $pid = $pm->start and next;

  my @ret = ();
  my $code = "use File::Where; \@ret = File::Where->where_pm(\"File::W
+here\");";
  eval $code;
  print $ret[0]."\n";
  $pm->finish;
}
$pm->wait_all_children;

        [download]
[reply]
[d/l]

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