Add Perdiodic Timer and nextiterationSleepingTime

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Add link to reactPhp

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review Fix

Add Note for old PHP version

README.md

@@ -1,14 +1,14 @@
 # DaemonBundle [![Build Status](https://travis-ci.org/M6Web/DaemonBundle.svg?branch=master)](https://travis-ci.org/M6Web/DaemonBundle)
 
-Allows you to create daemonized commands.
+Allows you to create daemonized commands with the [React event-loop component](https://github.com/reactphp/event-loop).
 
 ## Installation
 
 Via composer :
 
 ```json
 "require": {
-    "m6web/daemon-bundle":"^3.0"
+    "m6web/daemon-bundle":"^4.0"
 }
 ```
 
@@ -22,13 +22,15 @@ $bundles = [
 ];
 ```
 
-Note: For Symfony versions ">=2.3 && <3.0" support, you can use `"m6web/daemon-bundle":"^1.4"`.
-
+Note: 
+   - For Symfony versions ">=2.3 && <3.0" support, you can use `"m6web/daemon-bundle":"^1.4"`.
+   - For PHP versions ">=5.5.9 && <7.0" support, you can use `"m6web/daemon-bundle":"^3.0"`.
+
 ## Configuration
 
 You can optionally define events which are triggered each X iterations :
 
-```yml
+```yaml
 m6_web_daemon:
     iterations_events:
         -
@@ -41,6 +43,8 @@ m6_web_daemon:
 
 ## Write command
 
+This command use the [event-loop component](https://github.com/reactphp/event-loop#usage) which [ReactPHP](https://reactphp.org) uses to run loops and other asynchronous tasks.
+
 ```php
 <?php
 
@@ -64,6 +68,16 @@ class MyDaemonizedCommand extends DaemonCommand
 
         // Add your own optional callback : called every 10 iterations
         $this->addIterationsIntervalCallback(10, [$this, 'executeEveryTenLoops']);
+
+        // You can add your own Periodic Timer,
+        // Here this timer will be called every 0.5s
+        $daemon = $this;
+        $this->loop->addPeriodicTimer(0.5, function ($timer) use ($daemon) {
+            // It's the last loop, cancel the timer.
+            if ($daemon->isLastLoop()) {
+                $daemon->loop->cancelTimer($timer);
+            }
+        });
     }
 
     /**
@@ -72,8 +86,11 @@ class MyDaemonizedCommand extends DaemonCommand
     protected function execute(InputInterface $input, OutputInterface $output)
     {
         $output->writeln("Iteration");
-
-        usleep(100000);
+
+        // This method helps to give back the CPU to the react-loop (here for 1000 $µseconds).
+        // So you can wait between two iterations if your workers has nothing to do.
+
+        $this->setNextIterationSleepingTime(1000000); // Every seconds
     }
 
     /**