fork report child finish by order child process finish.

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

Hi All, I am testing the fork feature in the Linux. In below code out of 3 child parent randomly check one child and wait for it to finish and moves to another. I was wondering is it possible to make parent to report the child which finish first and another child that finish second and the third?

use strict;
use warnings;
use POSIX ":sys_wait_h";

handler();

sub handler
        {
        my %process = (
                        A => 'sleep 10 && exit 0',
                        B => 'sleep 15 && exit 0',
                        C => 'sleep 25 && exit 1',
                        );

        my @child_pids;
        foreach my $process(keys %process)
                {
                my $pid = fork;
                        if($pid)
                                {
                                #Parent.
                                #
                                print "Launched $process | $pid\n";
                                push(@child_pids, {PID => $pid, PROCES
+S => $process{$process}});
                                }
                        elsif($pid == 0)
                                {
                                exec $process{$process};
                                die "Can't exec $process";
                                }
                        else
                                {
                                #Parent
                                #       Fork failed.
                                die "cant fork $!\n";
                                }
                }
                foreach my $href (@child_pids)
                        {
                                print "Waiting $href->{PID} | $href->{
+PROCESS}\n";
                                while (waitpid($href->{PID}, WNOHANG) 
+== 0)
                                        {
                                        sleep 1;
                                        }
                                print "Failed $href->{PROCESS}\n" unle
+ss($? == 0);
                                print "Done $href->{PID} | $href->{PRO
+CESS}\n";
                        }
        }
[download]

Comment on fork report child finish by order child process finish. Download Code

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Re: fork report child finish by order child process finish. by aitap (Curate) on Sep 10, 2012 at 09:20 UTC
Unless you are training yourself, it should be easier to use Parallel::ForkManager and its `run_on_finish` callback. Manual way to do this is sequentially running waitpid with WHOHANG flag and checking its return value for all pids running. Example (untested): `foreach my $process (@child_pids) { if (waitpid($process->{PID}, WNOHANG)) { print "Process $process->{PROCESS} terminated\n"; } }` [download] Sorry if my advice was wrong.	[reply] [d/l] [select]
Re: fork report child finish by order child process finish. by locked_user sundialsvc4 (Abbot) on Sep 10, 2012 at 16:55 UTC
You are describing a Workflow management system ... the hard way. If the business situation is that “report #4 cannot start until reports #1 and #3 have finished,” and you find yourself writing custom Perl programs to shepherd that ... then you are “doing a thing that has already been done.”
Re: fork report child finish by order child process finish. by tart (Beadle) on Sep 11, 2012 at 02:41 UTC
Thanks aitap! Your advice definitely helped me to move further. Cheers!	[reply]