in reply to Tk and IPC - killing of process not working in Linux

I downloaded your script and ran it under the perl debugger on my linux box. As described the Cancel button did not kill the process.

I set a breakpoint on sub work(), and made a note of $pid, and the pid of the perl process.

  DB<1> b work
  DB<2> c
main::work(test.pl:12):         $pid = open PROC, 
main::work(test.pl:13):     'perl -le"$|=1; print and select(undef,und
+ef,undef,0.1) for 1 .. 1000" |'
main::work(test.pl:14):                 or die $!;
  DB<2> n
  DB<2> x $pid
0  9940
  DB<3> x $$                                    
0  9850

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From there, I ran pstree in a normal bash shell to check the child processes of the perl script:

/tmp$ pstree -apA 9850
perl,9850 -d -I /etc/perl -I /usr/local/lib/perl/5.10.1 -I /usr/local/
+share/perl/5.10.1 -I
  |-sh,9940 -c perl -le"$|=1; print and select(undef,undef,undef,0.1) 
+for 1 .. 1000"
  |   `-perl,9941 -le$|=1; print and select(undef,undef,undef,0.1) for
+ 1 .. 1000
  `-{perl},9939

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What this basically means, is that when you stated the test process, you actually started a shell which started the test process. It was the process ID of that shell that you had stored in $pid. When you sent a kill signal to that PID your killed the shell, but not it's child process.

I think you need to figure out how to start your process without going via a shell. I know you can do it via a fork/exec but that is probably to heavyweight and not portable to windows. There are probably other ways, but I don't know them off the top of my head. I suggest you read perlipc.

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Re^2: Tk and IPC - killing of process not working in Linux
by Dirk80 (Pilgrim) on Feb 13, 2011 at 15:53 UTC

    Thank you very much. The hint with the shell helps me a lot.

    Here a solution which is working for Linux and Windows:

    #!perl -slw
use strict;
use threads;
use threads::shared;
use Thread::Queue;

## A shared var to communicate progess between work thread and TK
my $Q = new Thread::Queue;
my $pid:shared;

sub work{

    if( $^O eq "linux" )
    {
        $pid = open PROC,
        "-|",
        "perl",
        "-le",
        '$|=1; print and select(undef,undef,undef,0.1) for 1 .. 1000'
            or die $!;
    }
    elsif( $^O eq "MSWin32" )
    {
        $pid = open PROC,
    'perl -le"$|=1; print and select(undef,undef,undef,0.1) for 1 .. 1
+000" |'
        or die $!;
    }
    else
    {
        die "Not implemented for $^O";
    }

    if( $pid ) {
        while( <PROC> ) {
            $Q->enqueue( $_ );
        }
        close PROC;
    }
}

threads->new( \&work )->detach;

## For lowest memory consumption require (not use)
## Tk::* after you've started the work thread.
use Tk;
use Tk::ProgressBar;

my $mw = MainWindow->new;
my $pb = $mw->ProgressBar()->pack();

my $repeat;
$repeat = $mw->repeat( 100 => sub {
    while( $Q->pending ) {
        my $progress = $Q->dequeue;
        return unless $progress;
        $repeat->cancel if $progress == 100;
        $pb->value( $progress )
    }
} );

$mw->Button('-text' => 'Cancel',
            '-command' => sub{ kill 9, $pid })->pack();

$mw->MainLoop;

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    In perlipc I read that if you give an open to minus more than 3 arguments, than the shell is not called.

    This solution is ok for me. But of course I'd prefer how to find out the pid of the process I want to kill. Independent whether it is called by a shell or not.

    And the other interesting question is why linux is using a shell and windows not?

    Greetings,

    Dirk

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