Improved java version of pi example also. See #1729

akka-docs/intro/getting-started-first-java.rst

@@ -237,13 +237,24 @@ e.g. in ``$AKKA_HOME/tutorial/akka/tutorial/first/java/Pi.java``.
 Creating the messages
 ---------------------
 
-The design we are aiming for is to have one ``Master`` actor initiating the computation, creating a set of ``Worker`` actors. Then it splits up the work into discrete chunks, and sends these chunks to the different workers in a round-robin fashion. The master waits until all the workers have completed their work and sent back results for aggregation. When computation is completed the master prints out the result, shuts down all workers and then itself.
+The design we are aiming for is to have one ``Master`` actor initiating the
+computation, creating a set of ``Worker`` actors. Then it splits up the work
+into discrete chunks, and sends these chunks to the different workers in a
+round-robin fashion. The master waits until all the workers have completed their
+work and sent back results for aggregation. When computation is completed the
+master sends the result to the ``Listener``, which prints out the result.
 
-With this in mind, let's now create the messages that we want to have flowing in the system. We need three different messages:
+With this in mind, let's now create the messages that we want to have flowing in
+the system. We need four different messages:
 
 - ``Calculate`` -- sent to the ``Master`` actor to start the calculation
-- ``Work`` -- sent from the ``Master`` actor to the ``Worker`` actors containing the work assignment
+- ``Work`` -- sent from the ``Master`` actor to the ``Worker`` actors containing
-- ``Result`` -- sent from the ``Worker`` actors to the ``Master`` actor containing the result from the worker's calculation
+  the work assignment
+- ``Result`` -- sent from the ``Worker`` actors to the ``Master`` actor
+  containing the result from the worker's calculation
+- ``PiApproximation`` -- sent from the ``Master`` actor to the
+  ``Listener`` actor containing the the final pi result and how long time
+  the calculation took
 
 Messages sent to actors should always be immutable to avoid sharing mutable state. So let's start by creating three messages as immutable POJOs. We also create a wrapper ``Pi`` class to hold our implementation:
 
@@ -285,19 +296,8 @@ Here is the master actor:
 
 A couple of things are worth explaining further.
 
-First, we are passing in a ``java.util.concurrent.CountDownLatch`` to the
+Note that we are passing in a ``ActorRef`` to the ``Master`` actor. This is used to
-``Master`` actor. This latch is only used for plumbing (in this specific
+report the the final result to the outside world.
-tutorial), to have a simple way of letting the outside world knowing when the
-master can deliver the result and shut down. In more idiomatic Akka code
-we would not use a latch but other abstractions and functions like ``Future``
-and ``ask()`` to achieve the same thing in a non-blocking way.
-But for simplicity let's stick to a ``CountDownLatch`` for now.
-
-Second, we are adding a couple of life-cycle callback methods; ``preStart`` and
-``postStop``. In the ``preStart`` callback we are recording the time when the
-actor is started and in the ``postStop`` callback we are printing out the result
-(the approximation of Pi) and the time it took to calculate it. In this call we
-also invoke ``latch.countDown()`` to tell the outside world that we are done.
 
 But we are not done yet. We are missing the message handler for the ``Master`` actor.
 This message handler needs to be able to react to two different messages:
@@ -310,15 +310,25 @@ The ``Calculate`` handler is sending out work to all the ``Worker`` via its rout
 The ``Result`` handler gets the value from the ``Result`` message and aggregates it to
 our ``pi`` member variable. We also keep track of how many results we have received back,
 and if that matches the number of tasks sent out, the ``Master`` actor considers itself done and
-invokes the ``self.stop()`` method to stop itself *and* all its supervised actors.
+sends the final result to the ``listener``. When done it also invokes the ``getContext().stop(getSelf())``
+method to stop itself *and* all its supervised actors.
 In this case it has one supervised actor, the router, and this in turn has ``nrOfWorkers`` supervised actors.
 All of them will be stopped automatically as the invocation of any supervisor's ``stop`` method
 will propagate down to all its supervised 'children'.
 
+
 Let's capture this in code:
 
 .. includecode:: ../../akka-tutorials/akka-tutorial-first/src/main/java/akka/tutorial/first/java/Pi.java#master-receive
 
+Creating the result listener
+----------------------------
+
+The listener is straightforward. When it receives the ``PiApproximation`` from the ``Master`` it
+prints the result and shuts down the ``ActorSystem``.
+
+.. includecode:: ../../akka-tutorials/akka-tutorial-first/src/main/java/akka/tutorial/first/java/Pi.java#result-listener
+
 Bootstrap the calculation
 -------------------------
 
@@ -329,11 +339,11 @@ invoke method ``calculate`` in which we start up the ``Master`` actor and wait f
 .. includecode:: ../../akka-tutorials/akka-tutorial-first/src/main/java/akka/tutorial/first/java/Pi.java#app
    :exclude: actors-and-messages
 
-As you can see the *calculate* method above it creates an ActorSystem and this is the Akka container which
+As you can see the *calculate* method above it creates an ``ActorSystem`` and this is the Akka container which
 will contain all actors created in that "context". An example of how to create actors in the container
-is the *'system.actorOf(...)'* line in the calculate method. In this case we create a top level actor.
+is the *'system.actorOf(...)'* line in the calculate method. In this case we create two top level actors.
 If you instead where in an actor context, i.e. inside an actor creating other actors, you should use
-*this.getContext.actorOf(...)*. This is illustrated in the Master code above.
+*getContext().actorOf(...)*. This is illustrated in the Master code above.
 
 That's it. Now we are done.
 
@@ -365,8 +375,8 @@ we compiled ourselves::
         -cp lib/scala-library.jar:lib/akka/akka-actor-2.0-SNAPSHOT.jar:. \
         akka.tutorial.java.first.Pi
 
-    Pi estimate:        3.1435501812459323
+    Pi approximation:   3.1435501812459323
-    Calculation time:   609 millis
+    Calculation time:   359 millis
 
 Yippee! It is working.
 
@@ -382,8 +392,8 @@ When this in done we can run our application directly inside Maven::
 
     $ mvn exec:java -Dexec.mainClass="akka.tutorial.first.java.Pi"
     ...
-    Pi estimate:        3.1435501812459323
+    Pi approximation:   3.1435501812459323
-    Calculation time:   597 millis
+    Calculation time:   359 millis
 
 Yippee! It is working.
 

akka-docs/intro/getting-started-first-scala-eclipse.rst

@@ -268,11 +268,16 @@ We start by creating case classes for each type of message in our application, s
 call it ``PiMessage``. Right click on the package and choose ``New Scala Class``, and enter ``PiMessage`` as
 the name of the class.
 
-We need three different messages:
+We need four different messages:
 
 - ``Calculate`` -- sent to the ``Master`` actor to start the calculation
-- ``Work`` -- sent from the ``Master`` actor to the ``Worker`` actors containing the work assignment
+- ``Work`` -- sent from the ``Master`` actor to the ``Worker`` actors containing
-- ``Result`` -- sent from the ``Worker`` actors to the ``Master`` actor containing the result from the worker's calculation
+  the work assignment
+- ``Result`` -- sent from the ``Worker`` actors to the ``Master`` actor
+  containing the result from the worker's calculation
+- ``PiApproximation`` -- sent from the ``Master`` actor to the
+  ``Listener`` actor containing the the final pi result and how long time
+  the calculation took
 
 Messages sent to actors should always be immutable to avoid sharing mutable state.
 In Scala we have 'case classes' which make excellent messages. So let's start by creating three messages as case classes.
@@ -343,19 +348,8 @@ Here is the master actor:
 
 A couple of things are worth explaining further.
 
-First, we are passing in a ``java.util.concurrent.CountDownLatch`` to the
+Note that we are passing in a ``ActorRef`` to the ``Master`` actor. This is used to
-``Master`` actor. This latch is only used for plumbing (in this specific
+report the the final result to the outside world.
-tutorial), to have a simple way of letting the outside world knowing when the
-master can deliver the result and shut down. In more idiomatic Akka code
-we would not use a latch but other abstractions and functions like ``Future``
-and ``?`` to achieve the same thing in a non-blocking way.
-But for simplicity let's stick to a ``CountDownLatch`` for now.
-
-Second, we are adding a couple of life-cycle callback methods; ``preStart`` and
-``postStop``. In the ``preStart`` callback we are recording the time when the
-actor is started and in the ``postStop`` callback we are printing out the result
-(the approximation of Pi) and the time it took to calculate it. In this call we
-also invoke ``latch.countDown()`` to tell the outside world that we are done.
 
 But we are not done yet. We are missing the message handler for the ``Master``
 actor. This message handler needs to be able to react to two different messages:
@@ -368,7 +362,8 @@ The ``Calculate`` handler is sending out work to all the ``Worker`` via its rout
 The ``Result`` handler gets the value from the ``Result`` message and aggregates it to
 our ``pi`` member variable. We also keep track of how many results we have received back,
 and if that matches the number of tasks sent out, the ``Master`` actor considers itself done and
-invokes the ``self.stop()`` method to stop itself *and* all its supervised actors.
+sends the final result to the ``listener``. When done it also invokes the ``context.stop(self)``
+method to stop itself *and* all its supervised actors.
 In this case it has one supervised actor, the router, and this in turn has ``nrOfWorkers`` supervised actors.
 All of them will be stopped automatically as the invocation of any supervisor's ``stop`` method
 will propagate down to all its supervised 'children'.
@@ -377,6 +372,13 @@ Let's capture this in code:
 
 .. includecode:: ../../akka-tutorials/akka-tutorial-first/src/main/scala/Pi.scala#master-receive
 
+Creating the result listener
+----------------------------
+
+The listener is straightforward. When it receives the ``PiApproximation`` from the ``Master`` it
+prints the result and shuts down the ``ActorSystem``.
+
+.. includecode:: ../../akka-tutorials/akka-tutorial-first/src/main/scala/Pi.scala#result-listener
 
 Bootstrap the calculation
 -------------------------
@@ -391,6 +393,12 @@ We also create a method ``calculate`` in which we start up the ``Master`` actor
 .. includecode:: ../../akka-tutorials/akka-tutorial-first/src/main/scala/Pi.scala#app
    :exclude: actors-and-messages
 
+As you can see the *calculate* method above it creates an ``ActorSystem`` and this is the Akka container which
+will contain all actors created in that "context". An example of how to create actors in the container
+is the *'system.actorOf(...)'* line in the calculate method. In this case we create two top level actors.
+If you instead where in an actor context, i.e. inside an actor creating other actors, you should use
+*context.actorOf(...)*. This is illustrated in the Master code above.
+
 That's it. Now we are done.
 
 Run it from Eclipse
@@ -401,8 +409,8 @@ If not, bring you project up to date by clicking ``Project/Build Project``. If t
 you can right-click in the editor where ``Pi`` is defined, and choose ``Run as.. /Scala application``.
 If everything works fine, you should see::
 
-    Pi estimate:        3.1435501812459323
+    Pi approximation:   3.1435501812459323
-    Calculation time:   632 millis
+    Calculation time:   359 millis
 
 You can also define a new Run configuration, by going to ``Run/Run Configurations``. Create a new ``Scala application``
 and choose the tutorial project and the main class to be ``akkatutorial.Pi``. You can pass additional command line

akka-docs/intro/getting-started-first-scala.rst

@@ -265,14 +265,14 @@ work and sent back results for aggregation. When computation is completed the
 master sends the result to the ``Listener``, which prints out the result.
 
 With this in mind, let's now create the messages that we want to have flowing in
-the system. We need three different messages:
+the system. We need four different messages:
 
 - ``Calculate`` -- sent to the ``Master`` actor to start the calculation
 - ``Work`` -- sent from the ``Master`` actor to the ``Worker`` actors containing
   the work assignment
 - ``Result`` -- sent from the ``Worker`` actors to the ``Master`` actor
   containing the result from the worker's calculation
-- ``PiEstimate`` -- sent from the ``Master`` actor to the
+- ``PiApproximation`` -- sent from the ``Master`` actor to the
   ``Listener`` actor containing the the final pi result and how long time
   the calculation took
 
@@ -361,7 +361,7 @@ Let's capture this in code:
 Creating the result listener
 ============================
 
-The listener is straightforward. When it receives the ``PiEstimate`` from the ``Master`` it
+The listener is straightforward. When it receives the ``PiApproximation`` from the ``Master`` it
 prints the result and shuts down the ``ActorSystem``.
 
 .. includecode:: ../../akka-tutorials/akka-tutorial-first/src/main/scala/Pi.scala#result-listener
@@ -418,8 +418,8 @@ compiled ourselves::
         -cp lib/scala-library.jar:lib/akka/akka-actor-2.0-SNAPSHOT.jar:. \
         akka.tutorial.first.scala.Pi
 
-    Pi estimate:        3.1435501812459323
+    Pi approximation:   3.1435501812459323
-    Calculation time:   553 millis
+    Calculation time:   359 millis
 
 Yippee! It is working.
 
@@ -437,8 +437,8 @@ When this in done we can run our application directly inside SBT::
 
     > run
     ...
-    Pi estimate:        3.1435501812459323
+    Pi approximation:   3.1435501812459323
-    Calculation time:   531 millis
+    Calculation time:   359 millis
 
 Yippee! It is working.
 

akka-tutorials/akka-tutorial-first/src/main/java/akka/tutorial/first/java/Pi.java

@@ -5,172 +5,193 @@
 package akka.tutorial.first.java;
 
 //#imports
-import akka.actor.Props;
+
 import akka.actor.ActorRef;
 import akka.actor.ActorSystem;
-import akka.actor.InternalActorRef;
+import akka.actor.Props;
 import akka.actor.UntypedActor;
 import akka.actor.UntypedActorFactory;
-import akka.japi.Creator;
+import akka.routing.RoundRobinRouter;
-import akka.routing.*;
+import akka.util.Duration;
-import akka.util.Timeout;
+import java.util.concurrent.TimeUnit;
 
-import java.util.LinkedList;
-import java.util.concurrent.CountDownLatch;
 //#imports
 
 //#app
 public class Pi {
 
-    public static void main(String[] args) throws Exception {
+  public static void main(String[] args) {
-        Pi pi = new Pi();
+    Pi pi = new Pi();
-        pi.calculate(4, 10000, 10000);
+    pi.calculate(4, 10000, 10000);
+  }
+
+  //#actors-and-messages
+  //#messages
+  static class Calculate {
+  }
+
+  static class Work {
+    private final int start;
+    private final int nrOfElements;
+
+    public Work(int start, int nrOfElements) {
+      this.start = start;
+      this.nrOfElements = nrOfElements;
     }
 
-    //#actors-and-messages
+    public int getStart() {
-    //#messages
+      return start;
-    static class Calculate {
     }
 
-    static class Work {
+    public int getNrOfElements() {
-        private final int start;
+      return nrOfElements;
-        private final int nrOfElements;
+    }
+  }
 
-        public Work(int start, int nrOfElements) {
+  static class Result {
-            this.start = start;
+    private final double value;
-            this.nrOfElements = nrOfElements;
-        }
 
-        public int getStart() {
+    public Result(double value) {
-            return start;
+      this.value = value;
-        }
-
-        public int getNrOfElements() {
-            return nrOfElements;
-        }
     }
 
-    static class Result {
+    public double getValue() {
-        private final double value;
+      return value;
-
-        public Result(double value) {
-            this.value = value;
-        }
-
-        public double getValue() {
-            return value;
-        }
     }
-    //#messages
+  }
 
-    //#worker
+  static class PiApproximation {
-    public static class Worker extends UntypedActor {
+    private final double pi;
+    private final Duration duration;
 
-        //#calculatePiFor
+    public PiApproximation(double pi, Duration duration) {
-        private double calculatePiFor(int start, int nrOfElements) {
+      this.pi = pi;
-            double acc = 0.0;
+      this.duration = duration;
-            for (int i = start * nrOfElements; i <= ((start + 1) * nrOfElements - 1); i++) {
-                acc += 4.0 * (1 - (i % 2) * 2) / (2 * i + 1);
-            }
-            return acc;
-        }
-        //#calculatePiFor
-
-        public void onReceive(Object message) {
-            if (message instanceof Work) {
-                Work work = (Work) message;
-                double result = calculatePiFor(work.getStart(), work.getNrOfElements());
-                getSender().tell(new Result(result));
-            } else {
-                throw new IllegalArgumentException("Unknown message [" + message + "]");
-            }
-        }
     }
-    //#worker
 
-    //#master
+    public double getPi() {
-    public static class Master extends UntypedActor {
+      return pi;
-        private final int nrOfMessages;
-        private final int nrOfElements;
-        private final CountDownLatch latch;
-
-        private double pi;
-        private int nrOfResults;
-        private long start;
-
-        private ActorRef router;
-
-        public Master(final int nrOfWorkers, int nrOfMessages,
-                      int nrOfElements, CountDownLatch latch) {
-            this.nrOfMessages = nrOfMessages;
-            this.nrOfElements = nrOfElements;
-            this.latch = latch;
-
-            //#create-router
-            router = this.getContext().actorOf(
-                new Props(Worker.class).withRouter(new RoundRobinRouter(nrOfWorkers)),
-                "pi");
-            //#create-router
-        }
-
-        //#master-receive
-        public void onReceive(Object message) {
-            //#handle-messages
-            if (message instanceof Calculate) {
-                for (int start = 0; start < nrOfMessages; start++) {
-                    router.tell(new Work(start, nrOfElements), getSelf());
-                }
-            } else if (message instanceof Result) {
-                Result result = (Result) message;
-                pi += result.getValue();
-                nrOfResults += 1;
-                if (nrOfResults == nrOfMessages) getContext().stop(getSelf());
-            } else throw new IllegalArgumentException("Unknown message [" + message + "]");
-            //#handle-messages
-        }
-        //#master-receive
-
-        @Override
-        public void preStart() {
-            start = System.currentTimeMillis();
-        }
-
-        @Override
-        public void postStop() {
-            System.out.println(String.format(
-                "\n\tPi estimate: \t\t%s\n\tCalculation time: \t%s millis",
-                pi, (System.currentTimeMillis() - start)));
-            latch.countDown();
-        }
     }
-    //#master
-    //#actors-and-messages
 
-    public void calculate(final int nrOfWorkers,
+    public Duration getDuration() {
-                          final int nrOfElements,
+      return duration;
-                          final int nrOfMessages)
-                          throws Exception {
-        // Create an Akka system
-        final ActorSystem system = ActorSystem.create();
-
-        // this latch is only plumbing to know when the calculation is completed
-        final CountDownLatch latch = new CountDownLatch(1);
-
-        // create the master
-        ActorRef master = system.actorOf(new Props(new UntypedActorFactory() {
-            public UntypedActor create() {
-                return new Master(nrOfWorkers, nrOfMessages, nrOfElements, latch);
-            }
-        }));
-
-        // start the calculation
-        master.tell(new Calculate());
-
-        // wait for master to shut down
-        latch.await();
-
-        // Shut down the system
-        system.shutdown();
     }
+  }
+
+  //#messages
+
+  //#worker
+  public static class Worker extends UntypedActor {
+
+    //#calculatePiFor
+    private double calculatePiFor(int start, int nrOfElements) {
+      double acc = 0.0;
+      for (int i = start * nrOfElements; i <= ((start + 1) * nrOfElements - 1); i++) {
+        acc += 4.0 * (1 - (i % 2) * 2) / (2 * i + 1);
+      }
+      return acc;
+    }
+
+    //#calculatePiFor
+
+    public void onReceive(Object message) {
+      if (message instanceof Work) {
+        Work work = (Work) message;
+        double result = calculatePiFor(work.getStart(), work.getNrOfElements());
+        getSender().tell(new Result(result), getSelf());
+      } else {
+        unhandled(message);
+      }
+    }
+  }
+
+  //#worker
+
+  //#master
+  public static class Master extends UntypedActor {
+    private final int nrOfMessages;
+    private final int nrOfElements;
+
+    private double pi;
+    private int nrOfResults;
+    private final long start = System.currentTimeMillis();
+
+    private final ActorRef listener;
+    private final ActorRef workerRouter;
+
+    public Master(final int nrOfWorkers, int nrOfMessages, int nrOfElements, ActorRef listener) {
+      this.nrOfMessages = nrOfMessages;
+      this.nrOfElements = nrOfElements;
+      this.listener = listener;
+
+      //#create-router
+      workerRouter = this.getContext().actorOf(new Props(Worker.class).withRouter(new RoundRobinRouter(nrOfWorkers)),
+          "workerRouter");
+      //#create-router
+    }
+
+    //#master-receive
+    public void onReceive(Object message) {
+      //#handle-messages
+      if (message instanceof Calculate) {
+        for (int start = 0; start < nrOfMessages; start++) {
+          workerRouter.tell(new Work(start, nrOfElements), getSelf());
+        }
+      } else if (message instanceof Result) {
+        Result result = (Result) message;
+        pi += result.getValue();
+        nrOfResults += 1;
+        if (nrOfResults == nrOfMessages) {
+          // Send the result to the listener
+          Duration duration = Duration.create(System.currentTimeMillis() - start, TimeUnit.MILLISECONDS);
+          listener.tell(new PiApproximation(pi, duration), getSelf());
+          // Stops this actor and all its supervised children
+          getContext().stop(getSelf());
+        }
+      } else {
+        unhandled(message);
+      }
+      //#handle-messages
+    }
+    //#master-receive
+  }
+
+  //#master
+
+  //#result-listener
+  public static class Listener extends UntypedActor {
+    public void onReceive(Object message) {
+      if (message instanceof PiApproximation) {
+        PiApproximation approximation = (PiApproximation) message;
+        System.out.println(String.format("\n\tPi approximation: \t\t%s\n\tCalculation time: \t%s",
+            approximation.getPi(), approximation.getDuration()));
+        getContext().system().shutdown();
+      } else {
+        unhandled(message);
+      }
+    }
+  }
+
+  //#result-listener
+  //#actors-and-messages
+
+  public void calculate(final int nrOfWorkers, final int nrOfElements, final int nrOfMessages) {
+    // Create an Akka system
+    ActorSystem system = ActorSystem.create("PiSystem");
+
+    // create the result listener, which will print the result and shutdown the system
+    final ActorRef listener = system.actorOf(new Props(Listener.class));
+
+    // create the master
+    ActorRef master = system.actorOf(new Props(new UntypedActorFactory() {
+      public UntypedActor create() {
+        return new Master(nrOfWorkers, nrOfMessages, nrOfElements, listener);
+      }
+    }), "master");
+
+    // start the calculation
+    master.tell(new Calculate());
+
+  }
 }
 //#app

akka-tutorials/akka-tutorial-first/src/main/scala/Pi.scala

@@ -5,7 +5,7 @@ package akka.tutorial.first.scala
 
 //#imports
 import akka.actor._
-import akka.routing._
+import akka.routing.RoundRobinRouter
 import akka.util.Duration
 import akka.util.duration._
 //#imports
@@ -21,7 +21,7 @@ object Pi extends App {
   case object Calculate extends PiMessage
   case class Work(start: Int, nrOfElements: Int) extends PiMessage
   case class Result(value: Double) extends PiMessage
-  case class PiEstimate(pi: Double, duration: Duration)
+  case class PiApproximation(pi: Double, duration: Duration)
   //#messages
 
   //#worker
@@ -52,21 +52,21 @@ object Pi extends App {
     val start: Long = System.currentTimeMillis
 
     //#create-router
-    val router = context.actorOf(
+    val workerRouter = context.actorOf(
-      Props[Worker].withRouter(RoundRobinRouter(nrOfWorkers)), name = "workers")
+      Props[Worker].withRouter(RoundRobinRouter(nrOfWorkers)), name = "workerRouter")
     //#create-router
 
     //#master-receive
     def receive = {
       //#handle-messages
       case Calculate ⇒
-        for (i ← 0 until nrOfMessages) router ! Work(i * nrOfElements, nrOfElements)
+        for (i ← 0 until nrOfMessages) workerRouter ! Work(i * nrOfElements, nrOfElements)
       case Result(value) ⇒
         pi += value
         nrOfResults += 1
         if (nrOfResults == nrOfMessages) {
           // Send the result to the listener
-          listener ! PiEstimate(pi, duration = (System.currentTimeMillis - start).millis)
+          listener ! PiApproximation(pi, duration = (System.currentTimeMillis - start).millis)
           // Stops this actor and all its supervised children
           context.stop(self)
         }
@@ -80,8 +80,8 @@ object Pi extends App {
   //#result-listener
   class Listener extends Actor {
     def receive = {
-      case PiEstimate(pi, duration) ⇒
+      case PiApproximation(pi, duration) ⇒
-        println("\n\tPi estimate: \t\t%s\n\tCalculation time: \t%s"
+        println("\n\tPi approximation: \t\t%s\n\tCalculation time: \t%s"
           .format(pi, duration))
         context.system.shutdown()
     }