how to autokill a hanging subprocess from a script

WindowBreaker · 07-10-2008, 04:34 PM

I have a perl script which launches a system command repeatedly from a looping control structure. Occasionally, one instance of that command will hang indefinitely until I manually kill it with 'pkill cmdname' from a shell. Then the loop will continue where it left off.

How can I execute a system command in perl, but autokill that command if it takes longer than 60 seconds to complete?

theNbomr · 07-10-2008, 10:22 PM

Something like this should get you started.

Code:

#! /usr/bin/perl -w
use strict;
use POSIX ":sys_wait_h";

    my $kidPid = fork();
    if( $kidPid ){
        print "Parent has child $kidPid\n";
        sleep( 10 );
        my $status = waitpid( -1, WNOHANG );
        print "Wait status: $status\n";
        if( 0 == $status ){
            print "Die, child ",$kidPid,"\n";
            kill( 9, $kidPid );
        }
    }
    else{
    
        # I'm the child
        my $i = 0;
        while( 1 ){
            print $i++,"\n";
            sleep 1;
        }

    }
    exit( 0 );

If the child process is an external program, you can launch it with exec().

--- rod.

Mr. C. · 07-10-2008, 10:25 PM

I'd be more inclined to discover why the script is hanging in the first place...

chrism01 · 07-11-2008, 12:25 AM

Mr C has a good point.
Going by the Perl principle of TMTOWTDI, you could also use IPC::Open2 (http://perldoc.perl.org/IPC/Open2.html) or even IPC::Open3 ( http://perldoc.perl.org/IPC/Open3.html) and wrap a SIGALRM ( http://perldoc.perl.org/functions/alarm.html) around it for closer control/checking.

WindowBreaker · 07-11-2008, 02:07 AM

Quote:

Originally Posted by Mr. C.

I'd be more inclined to discover why the script is hanging in the first place...

Good question. It's a compiled program called khtml2png2 used to gather screenshots. About 1 out of 20 times it will just hang for hours on end. I've compiled and ran the thing on multiple computers with different linux distro's - same problem.

Thanks to everyone for the responses. I ended up using perl's 'alarm' function. In the hopes that it will help somebody else, here's how I did it:

Code:

$SIG{ALRM} = \&timed_out;

eval{
 alarm(60);
 system('command';
 alarm(0);
};

sub timed_out{ die; }

Mr. C. · 07-11-2008, 02:16 AM

Ok, I see, it is someone else's poorly-written piece of software that hangs. Apparently, these issues have been around for a while with this software. You might want to report it to the author though.