mirror of
https://github.com/ChronosX88/FreePastry.git
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141 lines
5.5 KiB
HTML
141 lines
5.5 KiB
HTML
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<html><head>
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<title>FreePastry Tutorial</title>
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<link rel="stylesheet" href="tutorial.css" />
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</head>
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<body>
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<div class="content">
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<div class="frontmatter">
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<h1>The FreePastry Tutorial.</h1>
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<div class="abstract">This tutorial is designed to get you cooking quickly with the FreePastry
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API and software toolkit.</div>
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<h4>Version @tutorial_version@; @tutorial_date@. For <a
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href="http://freepastry.org/">FreePastry</a> version @freepastry_version@. Maintained by @maintainer@.</h4>
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</div>
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<div class="nav">
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<span class="nav-left"><a href="tut_multiple_nodes.html#lesson4">Previous (Multiple Nodes)</a></span>
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<span class="nav-center"><a href="index.html">Contents</a></span>
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<span class="nav-right"><a href="tut_scribe.html#scribe">Next (Scribe)</a></span>
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</div><br/><hr/>
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<a name="timer"><h1>Timer</h1></a>
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<h2>Scheduling tasks on the FreePastry timer.</h2>
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<h3>Download the tutorial files:
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<a href="./src/timer/DistTutorial.java">DistTutorial.java</a>,
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<a href="./src/timer/MyApp.java">MyApp.java</a> into a directory called rice/tutorial/timer/.</h3>
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<p/>This tutorial will show you how to schedule a task on the FreePastry thread. To be compatible
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with the commonAPI, the approach is to schedule a message to be sent to yourself at a regular interval.<br/>
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<p/>Let's start with the changes to MyApp.
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<p/>First a simple message.
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<pre>
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class MessageToSelf implements Message {
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public int getPriority() {
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return 0;
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}
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}
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</pre>
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<p/>Note that due to laziness, I have constructed this Message as an inner class
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of MyApp. This is fine for what we are going to use it for, but beware that
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it you will get a NotSerializableException if you attempt to send this
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message over the wire. While the Message may be serializable it has an implicit
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reference to MyApp, the containing class. When the message is serialized,
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FreePastry will also attempt to serialize MyApp which will fail and throw the
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exception.
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<p/>Here is the change to the constructor of MyApp, where we schedule the
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MessageToSelf. The first parameter is the <code>Message</code> that will be sent to
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MyApp. The second is the delay (in millis) until it is first sent. The third parameter
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is the period at which the message should be repeated.
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<pre>
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// Send MessageToSelf every 5 seconds, starting in 3 seconds
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messageToSelfTask = endpoint.scheduleMessage(new MessageToSelf(), 3000, 5000);
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</pre>
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<p/>As you can see, we have asked FreePastry to deliver the MessageToSelf in 3 seconds, and
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then continue to deliver it again every 5 seconds. Note that there is also a version
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of scheduleMessage() that doesn't take the 3rd parameter, and therefore doesn't repeat.
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<p/>We stored the task as a member variable so that we can
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cancel it later.
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<pre>
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CancellableTask messageToSelfTask;
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</pre>
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<p/>Whenever we receive the MessageToSelf we are just going to print out the current time.
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However, in your application you could call a method to do periodic maintenance, send
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messages to other nodes etc.
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<pre>
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public void deliver(Id id, Message message) {
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System.out.println(this+" received "+message);
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if (message instanceof MessageToSelf) {
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// This will get called every 5 seconds, on Pastry's thread.
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// Thus now we can assume we are on Pastry's thread.
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// TODO: whatever... send messages to other nodes? print out status?
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System.out.println("I got the MessageToSelf at time:"+System.currentTimeMillis());
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}
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}
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</pre>
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<p/>Finally, we make a public method to cancel the task.
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<pre>
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public void cancelTask() {
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messageToSelfTask.cancel();
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}
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</pre>
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<p/>The DistTutorial.java is based on lesson3, but we removed the code to print the leafset. For this
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example it is unnecessary to launch multiple pastry nodes, so we will only launch one. We added a bit of
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code after constructing the MyApp to cancel the task after 15 seconds.
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<pre>
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// construct a new MyApp
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MyApp app = new MyApp(node);
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// wait 15 seconds
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env.getTimeSource().sleep(15000);
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// cancel the task
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app.cancelTask();
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</pre>
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<p/>Ok, time to run it! Your output should resemble the following:
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<pre>
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<span class="input">java -cp .:FreePastry-@freepastry_version@.jar rice.tutorial.timer.DistTutorial 9001 localhost 9001</span>
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<span class="output">:1122932166578:Error connecting to address /10.9.8.7:9001: java.net.ConnectException: Connection refused: no further information
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:1122932166578:No bootstrap node provided, starting a new ring...
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Finished creating new node SocketNodeHandle (<0x3C1EEA..>/FOO/10.9.8.7:9001 [9038308767327354496])
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MyApp <0x3C1EEA..> received rice.tutorial.timer.MyApp$MessageToSelf@d70d7a
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I got the MessageToSelf at time:1115228553359
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MyApp <0x3C1EEA..> received rice.tutorial.timer.MyApp$MessageToSelf@d70d7a
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I got the MessageToSelf at time:1115228558359
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MyApp <0x3C1EEA..> received rice.tutorial.timer.MyApp$MessageToSelf@d70d7a
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I got the MessageToSelf at time:1115228563359
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</span></pre>
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<h3>Congratulations! Now you can schedule and cancel tasks without launching your own thread.</h3>
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<hr/><div class="nav">
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<span class="nav-left"><a href="tut_multiple_nodes.html#lesson4">Previous (Multiple Nodes)</a></span>
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<span class="nav-center"><a href="index.html">Contents</a></span>
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<span class="nav-right"><a href="tut_scribe.html#scribe">Next (Scribe)</a></span>
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</div><br/>
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<div class="footer">
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Pastry tutorial version @tutorial_version@. Last updated @tutorial_date@.
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For FreePastry @freepastry_version@. Maintained by @maintainer@.
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</div>
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</div>
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</body>
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</html>
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