How to use Parallel::ForkManager and Capture::Tiny together? - linux

Question

Below is a simplified example of my problem. Here exec should give an error because xecho doesn't exist.
Question
Is there a way to have Capture::Tiny capture the output from Parallel::ForkManager?
#!/usr/bin/perl
use strict;
use warnings;
use Parallel::ForkManager;
use Capture::Tiny 'capture';
my ($stdout, $stderr, $exit) = capture {
my $pm = Parallel::ForkManager->new(5);
my $pid = $pm->start;
if (!$pid) {
no warnings; # no warnings "exec" is not working
exec("xecho test");
$pm->finish;
}
};
print "$stdout\n";
print "$exit\n";
print "$stderr\n";

Answer 1

You cannot use Capture::Tiny to capture output from a child process, but you could use the run_on_finish method from Parallel::ForkManager :
use strict;
use warnings;
use Capture::Tiny qw(capture);
use Data::Dump;
use Parallel::ForkManager;
my $pm = Parallel::ForkManager->new(5);
$pm -> run_on_finish (
sub {
my (
$pid, $exit_code, $ident, $exit_signal,
$core_dump, $data_structure_reference
) = #_;
my $info = ${$data_structure_reference};
print "Received from child: \n";
dd $info;
}
);
my $pid = $pm->start;
if (!$pid) {
my ($stdout, $stderr, $exit) = capture {
sleep 4;
exec("xecho");
};
my $info = {stdout => $stdout, stderr => $stderr, exit=> $exit};
$pm->finish(0, \$info);
}
print "Master: waiting for child..\n";
$pm->wait_all_children;
Output:
Master: waiting for child..
Received from child:
{
exit => 0,
stderr => "Can't exec \"xecho\": No such file or directory at ./p.pl line 28.\n",
stdout => "",
}