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

Hi all

I'm currently using Parallel::ForkManager to perfom parallel operations. When I create a new child using the start method, I need to send the generated pid to the child process, however I cant do it (I know the start method returns the pid but this pid is not visible in the child process).

So, how can I know the pid in the child process?

And finally, How can I kill a child process? Sometimes in the wait_all_children method I get stuck beacuse the parent waits for a child that never ends. I need something to kill a child process if it runs more than 5m without finishing.

Thanks a lot.

Replies are listed 'Best First'.
Re: Parallel::ForkManager question
by ikegami (Patriarch) on Mar 13, 2008 at 22:20 UTC

    You want to know the child's PID in the child? $$.
    You want to know the parent's PID in the child? Just store $$ into a variable (say $ppid) before the loop.
    You want to know the child's PID in the parent? Use the snippet below. 

    for (...) {
   my $pid = $pm->start;
   if ($pid) {
      # We're in the parent.
      ...[ do something with $pid ]...
      next;
   }

   # We're in the child.
   ...
}

    [download]

    Update: Added third question and answer.

[reply]
[d/l]
[select]
Re: Parallel::ForkManager question
by pc88mxer (Vicar) on Mar 13, 2008 at 22:29 UTC
    You can collect the pids of all the children created by Parallel::ForkManager thusly: 
    my $parent_pid = $$;
my @pids;
my $pm = new Parallel::ForkManager($MAX_PROCESSES);
foreach $data (@all_data) {
  my $pid = $pm->start;
  if ($pid) {
      push(@pids, $pid);
      next;
  }
  # child executes here
  # ... and pid of parent is in $parent_pid
  $pm->finish; # child exits here
}
kill $signal, @pids; # signal children

    [download]
    This code also incorporates ikegami's comment about how the child can get the parent's pid.
[reply]
[d/l]
[select]
Re: Parallel::ForkManager question
by ctilmes (Vicar) on Mar 13, 2008 at 22:23 UTC
    Your PID is $$.

    You can kill a process with 'kill <signal>, <pid>', e.g. "kill 9 => 2713" (or "use Config; kill KILL => 2713;")

[reply]

Back to Seekers of Perl Wisdom