How can I timeout a forked process that might hang?

Question

I am writing a Perl script that will write some inputs and send those inputs to an external program. There is a small but non-zero chance that this program will hang, and I want

Answer 1

The above code (by strictlyrude27) didn't work out of the box, because -$PID is spelt in capitals. (BTW: there's also: http://www.gnu.org/software/coreutils/manual/html_node/timeout-invocation.html)

Here's an example with test:

#!/usr/bin/perl
use strict;
use warnings;
use File::Basename;

my $prg = basename $0;
my $num_secs_sleep = 2;
my $num_secs_to_timeout = 1;
my $orig_program = "sleep $num_secs_sleep; echo \"Look ma, survived!\"";
my $program = $orig_program;
my $expect = "";

if (@ARGV){
  if($ARGV[0] eq "test"){
    test();
    exit 0;
  } elsif (@ARGV == 1) {
    $num_secs_to_timeout = $ARGV[0];
  } elsif (@ARGV == 2) {
    $program = $ARGV[0];
    $num_secs_to_timeout = $ARGV[1];
  } else {
    die "Usage: $prg [ \"test\" | [program] seconds ] "
  }
}

if($orig_program eq $program) {
  if(@ARGV < 2) {
    $expect = $num_secs_to_timeout > $num_secs_sleep ?
      "(we expected to survive.)" : "(we expected to TIME OUT!)";
  }
  print STDERR "sleeping: $num_secs_sleep seconds$/";
}

print STDERR <', \$stdout or die "Can't open STDOUT: $!";
  Timed::timed("sleep 1", 3);
  is($stdout, undef);
  Timed::timed("sleep 2", 1);
  is($stdout, "TIME OUT!$/");
}

################################################################################
package Timed;
use strict;
use warnings;

sub timed {
  my $retval;
  my ($program, $num_secs_to_timeout) = @_;
  my $pid = fork;
  if ($pid > 0){ # parent process
    eval{
      local $SIG{ALRM} = 
        sub {kill 9, -$pid; print STDOUT "TIME OUT!$/"; $retval = 124;};
      alarm $num_secs_to_timeout;
      waitpid($pid, 0);
      alarm 0;
    };
    return defined($retval) ? $retval : $?>>8;
  }
  elsif ($pid == 0){ # child process
    setpgrp(0,0);
    exec($program);
  } else { # forking not successful
  }
}