akka---Getting Started Tutorial (Java): First Chapter
原文地址:http://doc.akka.io/docs/akka/2.0.2/intro/getting-started-first-java.html
Introduction
Welcome to the first tutorial on how to get started with Akka and Java. We assume that you already know what Akka and Java are and will now focus on the steps necessary to start your first project.
There are two variations of this first tutorial:
- creating a standalone project and run it from the command line
- creating a Maven project and running it from within Maven
Since they are so similar we will present them both.
The sample application that we will create is using actors to calculate the value of Pi. Calculating Pi is a CPU intensive operation and we will utilize Akka Actors to write a concurrent solution that scales out to multi-core processors. This sample will be extended in future tutorials to use Akka Remote Actors to scale out on multiple machines in a cluster.
We will be using an algorithm that is called “embarrassingly parallel” which just means that each job is completely isolated and not coupled with any other job. Since this algorithm is so parallelizable it suits the actor model very well.
Here is the formula for the algorithm we will use:
In this particular algorithm the master splits the series into chunks which are sent out to each worker actor to be processed. When each worker has processed its chunk it sends a result back to the master which aggregates the total result.
Tutorial source code
If you want don’t want to type in the code and/or set up a Maven project then you can check out the full tutorial from the Akka GitHub repository. It is in the akka-tutorials/akka-tutorial-first module. You can also browse it online here, with the actual source code here.
To check out the code using Git invoke the following command and you can then you can navigate down to the tutorial.
On Linux/Unix/Mac systems:
- $ git clone git://github.com/akka/akka.git
- $ cd akka/akka-tutorials/akka-tutorial-first
On Windows systems:
- C:\Users\jboner\src> git clone git://github.com/akka/akka.git
- C:\Users\jboner\src> cd akka\akka-tutorials\akka-tutorial-first
Prerequisites
This tutorial assumes that you have Java 1.6 or later installed on you machine and java on your PATH. You also need to know how to run commands in a shell (ZSH, Bash, DOS etc.) and a decent text editor or IDE to type in the Java code.
You need to make sure that $JAVA_HOME environment variable is set to the root of the Java distribution. You also need to make sure that the $JAVA_HOME/bin is on your PATH.
On Linux/Unix/Mac systems:
- $ export JAVA_HOME=..root of Java distribution..
- $ export PATH=$PATH:$JAVA_HOME/bin
You can test your installation by invoking java:
- $ java -version
- java version "1.6.0_24"
- Java(TM) SE Runtime Environment (build 1.6.0_24-b07-334-10M3326)
- Java HotSpot(TM) 64-Bit Server VM (build 19.1-b02-334, mixed mode)
On Windows systems:
- C:\Users\jboner\src\akka> set JAVA_HOME=..root of Java distribution..
- C:\Users\jboner\src\akka> set PATH=%PATH%;%JAVA_HOME%/bin
You can test your installation by invoking java:
- C:\Users\jboner\src\akka> java -version
- java version "1.6.0_24"
- Java(TM) SE Runtime Environment (build 1.6.0_24-b07-334-10M3326)
- Java HotSpot(TM) 64-Bit Server VM (build 19.1-b02-334, mixed mode)
Downloading and installing Akka
To build and run the tutorial sample from the command line, you have to download Akka. If you prefer to use SBT to build and run the sample then you can skip this section and jump to the next one.
Let’s get the akka-2.0.2.zip distribution of Akka from http://akka.io/downloads/ which includes everything we need for this tutorial. Once you have downloaded the distribution unzip it in the folder you would like to have Akka installed in. In my case I choose to install it in /Users/jboner/tools/, simply by unzipping it to this directory.
You need to do one more thing in order to install Akka properly: set the AKKA_HOME environment variable to the root of the distribution. In my case I’m opening up a shell, navigating down to the distribution, and setting theAKKA_HOME variable.
On Linux/Unix/Mac systems:
- $ cd /Users/jboner/tools/akka-2.0.2
- $ export AKKA_HOME=`pwd`
- $ echo $AKKA_HOME
- /Users/jboner/tools/akka-2.0.2
On Windows systems:
- C:\Users\jboner\src\akka> cd akka-2.0.2
- C:\Users\jboner\src\akka\akka-2.0.2> set AKKA_HOME=%cd%
- C:\Users\jboner\src\akka\akka-2.0.2> echo %AKKA_HOME%
- C:\Users\jboner\src\akka\akka-2.0.2
The distribution looks like this.
On Linux/Unix/Mac systems:
- $ ls -1
- bin
- config
- deploy
- doc
- lib
- src
On Windows systems:
- C:\Users\jboner\src\akka\akka-2.0.2> dir
- bin
- config
- deploy
- doc
- lib
- src
- In the bin directory we have scripts for starting the Akka Microkernel.
- In the config directory we have the Akka conf files.
- In the deploy directory we can place applications to be run with the microkernel.
- In the doc directory we have the documentation, API, and doc JARs.
- In the lib directory we have the Scala and Akka JARs.
- In the src directory we have the source JARs for Akka.
The only JAR we will need for this tutorial (apart from the scala-library.jar JAR) is the akka-actor-2.0.2.jar JAR in the lib/akka directory. This is a self-contained JAR with zero dependencies and contains everything we need to write a system using Actors.
Akka is very modular and has many JARs for containing different features. The modules are:
- akka-actor – Actors
- akka-remote – Remote Actors
- akka-slf4j – SLF4J Event Handler Listener for logging with SLF4J
- akka-testkit – Toolkit for testing Actors
- akka-kernel – Akka microkernel for running a bare-bones mini application server
- akka-durable-mailboxes – Durable mailboxes: file-based, MongoDB, Redis, Beanstalk and Zookeeper
Downloading and installing Maven
Maven is an excellent build system that can be used to build both Java and Scala projects. If you want to use Maven for this tutorial then follow the following instructions, if not you can skip this section and the next.
First browse to http://maven.apache.org/download.html and download the 3.0.3 distribution.
To install Maven it is easiest to follow the instructions on http://maven.apache.org/download.html#Installation.
Creating an Akka Maven project
If you have not already done so, now is the time to create a Maven project for our tutorial. You do that by stepping into the directory you want to create your project in and invoking the mvn command.
On Linux/Unix/Mac systems:
- $ mvn archetype:generate \
- -DgroupId=akka.tutorial.first.java \
- -DartifactId=akka-tutorial-first-java \
- -DarchetypeArtifactId=maven-archetype-quickstart \
- -DinteractiveMode=false
On Windows systems:
- C:\Users\jboner\src\akka\akka-2.0.2> mvn archetype:generate \
- -DgroupId=akka.tutorial.first.java \
- -DartifactId=akka-tutorial-first-java \
- -DarchetypeArtifactId=maven-archetype-quickstart \
- -DinteractiveMode=false
Now we have the basis for our Maven-based Akka project. Let’s step into the project directory.
On Linux/Unix/Mac systems:
- $ cd akka-tutorial-first-java
On Windows systems:
- C:\Users\jboner\src\akka\akka-2.0.2> cd akka-tutorial-first-java
Here is the layout that Maven created:
- akka-tutorial-first-jboner
- |-- pom.xml
- `-- src
- |-- main
- | `-- java
- | `-- akka
- | `-- tutorial
- | `-- first
- | `-- java
- | `-- App.java
As you can see we already have a Java source file called App.java, let’s now rename it to Pi.java.
We also need to edit the pom.xml build file. Let’s add the dependency we need as well as the Maven repository it should download it from. The Akka Maven repository can be found at http://akka.io/releases/ and Typesafe provides http://repo.typesafe.com/typesafe/releases/ that proxies several other repositories, including akka.io. It should now look something like this:
- <?xml version="1.0" encoding="UTF-8"?>
- <project xmlns="http://maven.apache.org/POM/4.0.0"
- xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
- xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
- http://maven.apache.org/xsd/maven-4.0.0.xsd">
- <modelVersion>4.0.0</modelVersion>
- <name>akka-tutorial-first-java</name>
- <groupId>akka.tutorial.first.java</groupId>
- <artifactId>akka-tutorial-first-java</artifactId>
- <packaging>jar</packaging>
- <version>1.0-SNAPSHOT</version>
- <url>http://akka.io</url>
- <dependencies>
- <dependency>
- <groupId>com.typesafe.akka</groupId>
- <artifactId>akka-actor</artifactId>
- <version>2.0.2</version>
- </dependency>
- </dependencies>
- <repositories>
- <repository>
- <id>typesafe</id>
- <name>Typesafe Repository</name>
- <url>http://repo.typesafe.com/typesafe/releases/</url>
- </repository>
- </repositories>
- <build>
- <plugins>
- <plugin>
- <groupId>org.apache.maven.plugins</groupId>
- <artifactId>maven-compiler-plugin</artifactId>
- <version>2.3.2</version>
- <configuration>
- <source>1.6</source>
- <target>1.6</target>
- </configuration>
- </plugin>
- </plugins>
- </build>
- </project>
Start writing the code
Now it’s about time to start hacking.
We start by creating a Pi.java file and adding these import statements at the top of the file:
- import akka.actor.ActorRef;
- import akka.actor.ActorSystem;
- import akka.actor.Props;
- import akka.actor.UntypedActor;
- import akka.actor.UntypedActorFactory;
- import akka.routing.RoundRobinRouter;
- import akka.util.Duration;
- import java.util.concurrent.TimeUnit;
If you are using Maven in this tutorial then create the file in the src/main/java/akka/tutorial/first/javadirectory.
If you are using the command line tools then create the file wherever you want. We will create it in a directory called tutorial at the root of the Akka distribution, 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 Workeractors. 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 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
- 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:
- 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;
- }
- public int getStart() {
- return start;
- }
- public int getNrOfElements() {
- return nrOfElements;
- }
- }
- static class Result {
- private final double value;
- public Result(double value) {
- this.value = value;
- }
- public double getValue() {
- return value;
- }
- }
- static class PiApproximation {
- private final double pi;
- private final Duration duration;
- public PiApproximation(double pi, Duration duration) {
- this.pi = pi;
- this.duration = duration;
- }
- public double getPi() {
- return pi;
- }
- public Duration getDuration() {
- return duration;
- }
- }
Creating the worker
Now we can create the worker actor. This is done by extending in the UntypedActor base class and defining the onReceive method. The onReceive method defines our message handler. We expect it to be able to handle the Work message so we need to add a handler for this message:
- public static class Worker extends UntypedActor {
- // 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);
- }
- }
- }
As you can see we have now created an UntypedActor with a onReceive method as a handler for the Workmessage. In this handler we invoke the calculatePiFor(..) method, wrap the result in a Result message and send it back to the original sender using getContext().reply(..). In Akka the sender reference is implicitly passed along with the message so that the receiver can always reply or store away the sender reference for future use.
The only thing missing in our Worker actor is the implementation on the calculatePiFor(..) method:
- 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;
- }
Creating the master
The master actor is a little bit more involved. In its constructor we create a round-robin router to make it easier to spread out the work evenly between the workers. Let’s do that first:
- workerRouter = this.getContext().actorOf(new Props(Worker.class).withRouter(new RoundRobinRouter(nrOfWorkers)),
- "workerRouter");
Now we have a router that is representing all our workers in a single abstraction. So now let’s create the master actor. We pass it three integer variables:
- nrOfWorkers – defining how many workers we should start up
- nrOfMessages – defining how many number chunks to send out to the workers
- nrOfElements – defining how big the number chunks sent to each worker should be
Here is the master actor:
- 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;
- workerRouter = this.getContext().actorOf(new Props(Worker.class).withRouter(new RoundRobinRouter(nrOfWorkers)),
- "workerRouter");
- }
- public void onReceive(Object message) {
- // handle messages ...
- }
- }
A couple of things are worth explaining further.
Note that we are passing in a ActorRef to the Master actor. This is used to report the the final result to the outside world.
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:
- Calculate – which should start the calculation
- Result – which should aggregate the different results
The Calculate handler is sending out work to all the Worker via its router.
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 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:
- public void onReceive(Object message) {
- 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);
- }
- }
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.
- 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);
- }
- }
- }
Please note that shutting down the actor system should be done by that part of the application which can safely determine that everything has been said and done. In this case, it is the Listener actor, but in other scenarios it might be the main thread or some other external service. It is by no means required to callsystem.shutdown() from within that system.
Bootstrap the calculation
Now the only thing that is left to implement is the runner that should bootstrap and run the calculation for us. We do that by adding a main method to the enclosing Pi class in which we create a new instance of Pi and invoke method calculate in which we start up the Master actor and wait for it to finish:
- public class Pi {
- public static void main(String[] args) {
- Pi pi = new Pi();
- pi.calculate(4, 10000, 10000);
- }
- // 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), "listener");
- // 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());
- }
- }
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 getContext().actorOf(...). This is illustrated in the Master code above.
That’s it. Now we are done.
Before we package it up and run it, let’s take a look at the full code now, with package declaration, imports and all:
- /**
- * Copyright (C) 2009-2012 Typesafe Inc. <http://www.typesafe.com>
- */
- package akka.tutorial.first.java;
- import akka.actor.ActorRef;
- import akka.actor.ActorSystem;
- import akka.actor.Props;
- import akka.actor.UntypedActor;
- import akka.actor.UntypedActorFactory;
- import akka.routing.RoundRobinRouter;
- import akka.util.Duration;
- import java.util.concurrent.TimeUnit;
- public class Pi {
- public static void main(String[] args) {
- Pi pi = new Pi();
- pi.calculate(4, 10000, 10000);
- }
- 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;
- }
- public int getStart() {
- return start;
- }
- public int getNrOfElements() {
- return nrOfElements;
- }
- }
- static class Result {
- private final double value;
- public Result(double value) {
- this.value = value;
- }
- public double getValue() {
- return value;
- }
- }
- static class PiApproximation {
- private final double pi;
- private final Duration duration;
- public PiApproximation(double pi, Duration duration) {
- this.pi = pi;
- this.duration = duration;
- }
- public double getPi() {
- return pi;
- }
- public Duration getDuration() {
- return duration;
- }
- }
- public static class Worker extends UntypedActor {
- 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;
- }
- 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);
- }
- }
- }
- 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;
- workerRouter = this.getContext().actorOf(new Props(Worker.class).withRouter(new RoundRobinRouter(nrOfWorkers)),
- "workerRouter");
- }
- public void onReceive(Object message) {
- 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);
- }
- }
- }
- 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);
- }
- }
- }
- 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), "listener");
- // 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());
- }
- }
Run it as a command line application
If you have not typed in (or copied) the code for the tutorial as$AKKA_HOME/tutorial/akka/tutorial/first/java/Pi.java then now is the time. When that’s done open up a shell and step in to the Akka distribution (cd $AKKA_HOME).
First we need to compile the source file. That is done with Java’s compiler javac. Our application depends on the akka-actor-2.0.2.jar and the scala-library.jar JAR files, so let’s add them to the compiler classpath when we compile the source.
On Linux/Unix/Mac systems:
- $ javac -cp lib/scala-library.jar:lib/akka/akka-actor-2.0.2.jar tutorial/akka/tutorial/first/java/Pi.java
On Windows systems:
- C:\Users\jboner\src\akka\akka-2.0.2> javac -cp \
- lib/scala-library.jar;lib/akka/akka-actor-2.0.2.jar \
- tutorial/akka/tutorial/first/java/Pi.java
When we have compiled the source file we are ready to run the application. This is done with java but yet again we need to add the akka-actor-2.0.2.jar and the scala-library.jar JAR files to the classpath as well as the classes we compiled ourselves.
On Linux/Unix/Mac systems:
- $ java \
- -cp lib/scala-library.jar:lib/akka/akka-actor-2.0.2.jar:. \
- akka.tutorial.first.scala.Pi
- Pi approximation: 3.1415926435897883
- Calculation time: 359 millis
On Windows systems:
- C:\Users\jboner\src\akka\akka-2.0.2> java \
- -cp lib/scala-library.jar;lib\akka\akka-actor-2.0.2.jar;. \
- akka.tutorial.first.scala.Pi
- Pi approximation: 3.1415926435897883
- Calculation time: 359 millis
Yippee! It is working.
Run it inside Maven
If you used Maven, then you can run the application directly inside Maven. First you need to compile the project.
On Linux/Unix/Mac systems:
- $ mvn compile
On Windows systems:
- C:\Users\jboner\src\akka\akka-2.0.2> mvn compile
When this in done we can run our application directly inside Maven.
On Linux/Unix/Mac systems:
- $ mvn exec:java -Dexec.mainClass="akka.tutorial.first.java.Pi"
- ...
- Pi approximation: 3.1415926435897883
- Calculation time: 359 millis
On Windows systems:
- C:\Users\jboner\src\akka\akka-2.0.2> mvn exec:java \
- -Dexec.mainClass="akka.tutorial.first.java.Pi"
- ...
- Pi approximation: 3.1415926435897883
- Calculation time: 359 millis
Yippee! It is working.
Overriding Configuration Externally (Optional)
The sample project includes an application.conf file in the resources directory:
- akka.actor.deployment {
- /master/workerRouter {
- # Uncomment the following two lines to change the calculation to use 10 workers instead of 4:
- #router = round-robin
- #nr-of-instances = 10
- }
- }
If you uncomment the two lines, you should see a change in performance, hopefully for the better (you might want to increase the number of messages in the code to prolong the time the application runs). It should be noted that overriding only works if a router type is given, so just uncommenting nr-of-instances does not work; see Routing (Java) for more details.
Note
Make sure that your application.conf is on the class path when you run the application. If running from inside Maven that should already be the case, otherwise you need to add the directory containing this file to the JVM’s -classpath option.
Conclusion
We have learned how to create our first Akka project using Akka’s actors to speed up a computation-intensive problem by scaling out on multi-core processors (also known as scaling up). We have also learned to compile and run an Akka project using either the tools on the command line or the SBT build system.
If you have a multi-core machine then I encourage you to try out different number of workers (number of working actors) by tweaking the nrOfWorkers variable to for example; 2, 4, 6, 8 etc. to see performance improvement by scaling up.
Happy hakking.
akka---Getting Started Tutorial (Java): First Chapter的更多相关文章
- Thinking in Java from Chapter 15
From Thinking in Java 4th Edition. 泛型实现了:参数化类型的概念,使代码可以应用于多种类型.“泛型”这个术语的意思是:“适用于许多许多的类型”. 如果你了解其他语言( ...
- Thinking in Java from Chapter 11
From Thinking in Java 4th Edition 持有对象 // Simple container example (produces compiler warnings.) // ...
- Thinking in Java from Chapter 21
From Thinking in Java 4th Edition 并发 线程可以驱动任务,因此你需要一种描述任务的方式,这可由Runnable接口来提供. 要想定义任务,只需要实现Runnable接 ...
- Thinking in Java from Chapter 7
From Thinking in Java 4th Edition final 1. 对于基本类型,final使数值恒定不变 2. 对于对象引用,final使引用恒定不变,即不能指向别的对象,但指向的 ...
- Thinking in Java from Chapter 10
From Thinking in Java 4th Edition 内部类 public class Parcel1 { class Contents { private int i = 11; pu ...
- java1234教程系列笔记 S1 Java SE chapter 02 写乘法口诀表
一.水仙花数 1.方式一:这是我的思路,取各个位数的方式.我个人习惯于使用取模运算. public static List<Integer> dealNarcissiticNumberMe ...
- java1234教程系列笔记 S1 Java SE chapter 02 lesson 03 java基本数据类型
第二章 第三节 数据类型 3.1 分类 基本数据类型.引用类型 3.2整型 byte 8 short 16 int 32 long 64 作业: A:1-10求和 B:float double 的最 ...
- AKKA文档2.1(java版)——什么是AKKA?
可扩展的实时事务处理 我们相信编写并发.容错.可扩展的应用相当的困难.盖因大多数时候我们一直在使用错误的工具和错误的抽象等级.AKKA就是为了改变这一切的.我们利用角色模型提升了抽象等级,并且提供了一 ...
- 【转】O'Reilly Java系列书籍建议阅读顺序(转自蔡学庸)
Learning Java the O'Reilly's Way (Part I) Java 技术可以说是越来越重要了,不但可以用在计算机上,甚至连电视等家电用品,行动电话.个人数字助理(PDA)等电 ...
随机推荐
- 验证list的底层数据结构
<STL源代码剖析>中,指出SGI STL的list底层数据结构式循环双向链表.而且在链表尾端留一个空白节点.让end指向它.因为是双向的,那么list的迭代器必须是Bidirection ...
- 项目: python爬虫 福利 煎蛋网妹子图
嘿嘿嘿! 嘿嘿嘿! 福利一波, 之前看小甲鱼的python教学视频的时候, 看到上面教的爬虫, 爬美女图片的, 心很痒痒, 但是不知道为啥, 按照视频一个字一个字敲的代码,总是报错, 有一天花了 一下 ...
- Python爬虫之『urlopen』
本文以爬取百度首页为示例来学习,python版本为python3.6.7,完整代码会在文章末附上 本次学习所用到的python框架:urllib.request 本次学习所用到的函数: urllib. ...
- 洛谷 P1553 数字反转(升级版)
P1553 数字反转(升级版) 题目描述 给定一个数,请将该数各个位上数字反转得到一个新数. 这次与NOIp2011普及组第一题不同的是:这个数可以是小数,分数,百分数,整数.整数反转是将所有数位对调 ...
- C++怎么访问私有变量和函数
用指针呀,了解C++内存结构的话. 1. 对于私有成员变量,可以用指针来访问. 2. 对于虚函数,也可以用指针来访问. 3. 另外,对于私有成员,如果摸不准地址构造,可以先构造一个结构相似的类,然后增 ...
- 01-Jvm 内存区域复习笔记
Java内存区域 1.程序计数器(Program Counter Register) 在虚拟机中一块较小的内存空间.它的作用能够看做是当前线程所运行的字节码的行号指示 ...
- php课程 12-42 php中类的关键字有哪些
php课程 12-42 php中类的关键字有哪些 一.总结 一句话总结:const.final.static 1.类常量-const2.最终版本-final3.静态成员-static 1.php中类常 ...
- Jmeter使用_处理响应结果显示乱码
1. 添加BeanShell PostProcessor 输入prev.setDataEncoding("utf-8"); 目的是修改响应数据编码格式为utf-8,保存
- 洛谷 P1679 神奇的四次方数
P1679 神奇的四次方数 题目描述 在你的帮助下,v神终于帮同学找到了最合适的大学,接下来就要通知同学了.在班级里负责联络网的是dm同学,于是v神便找到了dm同学,可dm同学正在忙于研究一道有趣的数 ...
- 《ZigBee Wireless Networking》学习笔记【1】
<ZigBee Wireless Networking>这本书对ZigBee技术阐释地比較全面,强烈推荐各位同仁阅读. 这本书的电子版请点击以下链接下载: 1,下图是该书中对ZigBee, ...