Keeping an eye on hung system calls..

Steve Keay london-pm-steve at
Tue Jun 6 12:31:45 BST 2006

On Tue, Jun 06, 2006 at 11:14:06AM +0100, Toby Corkindale wrote:
> Two methods we've thought of so far:
> 1) fork() prior to calling system() (or exec()), and then call alarm() before
>    waiting for the child to finish, or killing it from the alarm sighandler.

The following code seems to work on a linux box, and uses a pipe to
avoid messy signal handling issues.  I have no idea how portable this
is, and I'm sure that there is somthing better on CPAN.

use strict;
use IO::Select;

my $child_work_time = shift || 2;
my $timeout = 5;

warn "Process $$ forking...\n";
my $pid = open my $fh, "-|";
defined $pid or die "open: $!";
if ($pid == 0){
    open my $handle, ">&STDOUT";
    open STDOUT, ">&STDERR";
    warn "Process $$ working...\n";
    # -- in real life we would exec("mplayer") or die here --
    sleep $child_work_time;
    warn "Process $$ finished, exiting\n";
} else {
    if (IO::Select->new($fh)->can_read($timeout)){
        warn "Process $$ - child $pid has exited.\n";
    } else {
        warn "Process $$ timeout - killing child $pid.\n";
        kill 9, $pid or warn "kill 9, $pid: $!";

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