Add tiny tick timer to example

Author: Greg Bowler

example/02-countdown.php

@@ -3,6 +3,10 @@
  * This example shows how a PeriodicTimer can be used to schedule ticks
  * forever, combined with an IndividualTimer that will cause the loop to halt
  * after a specified period.
+ *
+ * To articulate the use of asynchronous methods, a "tiny tick timer" is
+ * introduced that runs very frequently, alongside the countdown. You can
+ * imagine the concurrent timers being used to execute actual workloads.
  */
 
 use Gt\Async\Loop;
@@ -13,6 +17,7 @@
 
 $stopTimer = new IndividualTimer(5);
 $periodicTimer = new PeriodicTimer(1, true);
+$tinyTickTimer = new PeriodicTimer(0.1, true);
 $countdownNumber = 5;
 
 $loop = new Loop();
@@ -21,12 +26,16 @@
 	echo "Countdown: $countdownNumber", PHP_EOL;
 	$countdownNumber--;
 });
+$tinyTickTimer->addCallback(function() {
+	echo ".";
+});
 $stopTimer->addCallback(function() use($loop) {
 	echo "LIFT OFF!", PHP_EOL;
 	$loop->halt();
 });
 
 $loop->addTimer($periodicTimer);
+$loop->addTimer($tinyTickTimer);
 $loop->addTimer($stopTimer);
 echo "Starting...", PHP_EOL;
 $loop->run();