Ways to do timeouts in Perl?

Question

I frequently use the following pattern to set an upper bound to the running time of a particular code fragment in Perl:

my $TIMEOUT_IN_SECONDS = 5;
eval {
           


        

Answer 1

Take care with signal handling. Perl receives signals asynchronously and they may be lost or interfere with each other if a signal is received while another signal is being handled by the callback.

Event-handling libraries' Win32 support is pretty so-so in Perl (I have to support non-cygwin Win32), so I generally use a simple polling loop for timeouts:

use Time::HiRes qw(sleep);

sub timeout {
  my $timeout = shift;
  my $poll_interval = shift;
  my $test_condition = shift;
  until ($test_condition->() || $timeout <= 0) {
    $timeout -= $poll_interval;
    sleep $poll_interval;
  }
  return $timeout > 0; # condition was met before timeout
}

my $success = timeout(30, 0.1, \&some_condition_is_met);

The sleep timer can be easily made user- or caller-configurable and unless you are doing an extremely tight loop or have multiple callers waiting on the loop (where you can end up with a race or dead lock), it is a simple, reliable, and cross-platform way to implement a timeout.

Also note that the loop overhead will mean that you cannot guarantee that the timeout is observed absolutely. $test_condition, the decrement, garbage collection, etc. can interfere.