Or maybe you want to prevent the child from running longer than a certain amount of time. 

use strict;
use warnings;

use IO::Select  qw( );
use IPC::Open2  qw( open2 );
use Time::HiRes qw( time );   # Optional

my $timeout    = 30.000;   # Abort after this many seconds.
my $command    = '...';    # The command to execute.
my $from_child = '';       # Receives the output of the command.

my $pid = open2(undef, my $fh_from_child, $command);
my $sel = IO::Select->new($fh_from_child);
my $abort_time = time + $timeout;
for (;;) {
   my $time_left = $abort_time - time;
   my @r = $time_left > 0 ? $sel->can_read($time_left): ();
   if (!@r) {
      kill(TERM => $pid);
      die("Child took more than $timeout seconds.\n");
   }

   read($fh_from_child, $from_child, 4096, length($from_child))
      or last;
}

print($from_child);

waitpid($pid, 0);

[download]

Also tested. Also won't work on Windows.

Update: Added call to kill. Could still use some work there.

Update: Or maybe you want to give a notice at a fixed interval? It should be easy to combine the techniques used in each of my posts to do this.

In reply to Re: Threads or no Threads (total timeout) by ikegami
in thread Threads or no Threads by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.