I have a *nix program that emulates 'top' in that it continually loops and renders data in a shell window. The program starts, and creates three threads which gather distinct information, update a global shared hash, sleep for some period, and then repeat. The sleep is there because I don't want to hammer the resources.

A fourth thread renders all the shared global data, sleeps and repeats, while the main program loops and performs a non-blocking read to see if a key has been pressed. If 'q' has, then it sets a shared global $quit = 1, then joins the threads and exits.

The effect is one of pretty, blinking lights, that demo well. The program is performing very well, except that when I press 'q', all the threads are looping and sleeping, and only get to check $quit between sleep calls. This means that there is a delay (of up to 10 seconds) until all threads wake up and notice $quit == 1.

As I see it, I could simply exit as soon as I see a 'q' pressed, but that seems untidy. Is there a way to avoid the delay, and interrupt all the sleep calls? Could someone suggest an entirely better way of doing this? (Code simplified for brevity). 

  #! /usr/bin/perl -w
  use strict;
  use threads;  
  use threads::shared;
  use Term::ReadKey;

  my $quit : shared = 0;
  
  sub gatherData1 { while (!$quit) {... sleep 1}  }
  sub gatherData2 { while (!$quit) {... sleep 5}  }
  sub gatherData3 { while (!$quit) {... sleep 10} }
  sub renderData  { while (!$quit) {... sleep 1}  }

  my $gatherer1 = threads->new (\&gatherData1);
  my $gatherer2 = threads->new (\&gatherData2);
  my $gatherer3 = threads->new (\&gatherData3);
  my $renderer  = threads->new (\&renderData);

  while (!$quit)
  {
    ReadMode 'cbreak';
    $quit = 1 if defined (my $char = ReadKey (0)) && $char eq 'q';
    ReadMode 'normal';
  }

  $gatherer1->join;
  $gatherer2->join;
  $gatherer3->join;
  $renderer->join;
  exit 0;

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In reply to Dormus interruptus by pbeckingham

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