# standard script to revive hanging processes

# cleanup and die function

sub cleanup($file, $reason) {

        ($file, $reason) = (shift, shift);

        print "unlink: $file\n";

        unlink $file; print $reason."\n"; exit;
}

# start-background-process helper

sub background($cmdline) {

        ($cmdline) = (shift);

        print "background: $cmdline\n";

        defined($pid = fork) or die "$!"; return if $pid;

        setsid or die "$!";

        exec "$cmdline"; exit;
}

# main process loop, make it happen

$cmd = shift or die "no command specified!";

print "revive: starting ($cmd)\n";

# store current process list

$tmp = "/tmp/keepalive".time();

`ps -waxopgid,args > $tmp`;

# revive (kill and restart) specified command

open(LIST, "<$tmp") or &cleanup($tmp, "$!");

while(<LIST>) {

        next if /revive/;

        next unless /([0-9]+).*($cmd.*)$/;

        # running, revive it (kill and restart)

        ($pid, $cmd, $revived) = ($1, $2, ++$revived);

        print "restarting: $pid\n";

        kill -15, $pid; &background("$cmd");
}

&cleanup($tmp, "finished") if $revived;

&background("$cmd") unless $revived;

&cleanup($tmp, "finished");