Fork/Join Framework Tutorial: ForkJoinPool Example

灰太狼 2022-08-10 13:45 113阅读 0赞

[JAVA 7 FEATURES][], [MULTI THREADING][]

# Fork/Join Framework Tutorial: ForkJoinPool Example #

[MAY 27, 2014][MAY 27_ 2014]  [LOKESH][] [\+][Link 1]  [2 COMMENTS][]

The effective use of parallel cores in a Java program has always been a challenge. There were few home-grown frameworks that would distribute the work across multiple cores and then join them to return the result set. Java 7 has incorporated this feature as a [Fork and Join framework][].

Basically the Fork-Join breaks the task at hand into mini-tasks until the mini-task is simple enough that it can be solved without further breakups. It’s like a [divide-and-conquer algorithm][]. One important concept to note in this framework is that ideally no worker thread is idle. They implement a [work-stealing algorithm][] in that idle workers `steal` the work from those workers who are busy.

![Fork Join Framework][]

Fork Join Framework

It’s based on the work of Doug Lea, a thought leader on Java concurrency. Fork/Join deals with the threading hassles; you just indicate to the framework which portions of the work can be broken apart and handled recursively. It employs pseudocode (as taken from Doug Lea’s paper on the subject):

Result solve(Problem problem) {
    	if (problem is small)
    		directly solve problem
    	else {
    		split problem into independent parts
    		fork new subtasks to solve each part
    		join all subtasks
    		compose result from subresults
    	}
    }

Discussion Points
    
    1) Core Classes used in Fork/Join Framework
        i)  ForkJoinPool
        ii) ForkJoinTask
    2) Example Implementations of Fork/Join Pool Framework
        i)  Implementation Sourcecode
        ii) How it works?
    3) Difference between Fork/Join Framework And ExecutorService
    4) Existing Implementations in JDK
    5) Conclusion

## Core Classes used in Fork/Join Framework ##

The core classes supporting the Fork-Join mechanism are `ForkJoinPool` and `ForkJoinTask`.

Let’s learn about their roles in detail.

### ForkJoinPool ###

The `ForkJoinPool` is basically a specialized implementation of `ExecutorService` implementing the work-stealing algorithm we talked about above. We create an instance of `ForkJoinPool` by providing the target parallelism level i.e. the number of processors as shown below:

> ForkJoinPool pool = new ForkJoinPool(numberOfProcessors);
> 
>  
> 
> Where numberOfProcessors = Runtime.getRunTime().availableProcessors();

If you use a no-argument constructor, by default, it creates a pool of size that equals the number of available processors obtained using above technique.

Although you specify any initial pool size, the pool adjusts its size dynamically in an attempt to maintain enough active threads at any given point in time. Another important difference compared to other `ExecutorService's` is that this pool need not be explicitly shutdown upon program exit because all its threads are in daemon mode.

There are three different ways of submitting a task to the `ForkJoinPool`.

1) execute() method //Desired asynchronous execution; call its fork method to split the work between multiple threads.  
2) invoke() method: //Await to obtain the result; call the invoke method on the pool.  
3) submit() method: //Returns a Future object that you can use for checking status and obtaining the result on its completion.

### ForkJoinTask ###

This is an abstract class for creating tasks that run within a `ForkJoinPool`. The `Recursiveaction` and `RecursiveTask` are the only two direct, known subclasses of `ForkJoinTask`. The only difference between these two classes is that the `RecursiveAction` does not return a value while `RecursiveTask` does have a return value and returns an object of specified type.

> In both cases, you would need to implement the compute method in your subclass that performs the main computation desired by the task.

The `ForkJoinTask` class provides several methods for checking the execution status of a task. The isDone() method returns true if a task completes in any way. The isCompletedNormally() method returns true if a task completes without cancellation or encountering an exception, and isCancelled() returns true if the task was cancelled. Lastly, isCompletedabnormally() returns true if the task was either cancelled or encountered an exception.

## Example Implementations of Fork/Join Pool Framework ##

In this example, you will learn how to use the asynchronous methods provided by the `ForkJoinPool` and `ForkJoinTask` classes for the management of tasks. You are going to implement a program that will search for files with a determined extension inside a folder and its subfolders. The `ForkJoinTask` class you’re going to implement will process the content of a folder. For each subfolder inside that folder, it will send a new task to the `ForkJoinPool` class in an asynchronous way. For each file inside that folder, the task will check the extension of the file and add it to the result list if it proceeds.

The solution to above problem is implemented in `FolderProcessor` class, which is given below:

### Implementation Sourcecode ###

FolderProcessor.java

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      <code style="">package</code> 
      <code style="">forkJoinDemoAsyncExample;</code> 
     </div> 
     <div style="">
       &nbsp; 
     </div> 
     <div style=""> 
      <code style="">import</code> 
      <code style="">java.io.File;</code> 
     </div> 
     <div style=""> 
      <code style="">import</code> 
      <code style="">java.util.ArrayList;</code> 
     </div> 
     <div style=""> 
      <code style="">import</code> 
      <code style="">java.util.List;</code> 
     </div> 
     <div style=""> 
      <code style="">import</code> 
      <code style="">java.util.concurrent.RecursiveTask;</code> 
     </div> 
     <div style="">
       &nbsp; 
     </div> 
     <div style=""> 
      <code style="">public</code> 
      <code style="">class</code> 
      <code style="">FolderProcessor </code> 
      <code style="">extends</code> 
      <code style="">RecursiveTask&lt;List&lt;String&gt;&gt;</code> 
     </div> 
     <div style=""> 
      <code style="">{ </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">private</code> 
      <code style="">static</code> 
      <code style="">final</code> 
      <code style=""> long</code> 
      <code style="">serialVersionUID = 1L;</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//This attribute will store the full path of the folder this task is going to process.</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">private</code> 
      <code style="">final</code> 
      <code style="">String&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; path;</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//This attribute will store the name of the extension of the files this task is going to look for.</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">private</code> 
      <code style="">final</code> 
      <code style="">String&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; extension;</code> 
     </div> 
     <div style="">
       &nbsp; 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//Implement the constructor of the class to initialize its attributes</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">public</code> 
      <code style="">FolderProcessor(String path, String extension)</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">{ </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">this</code> 
      <code style="">.path = path;</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">this</code> 
      <code style="">.extension = extension;</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">}</code> 
     </div> 
     <div style="">
       &nbsp; 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//Implement the compute() method. As you parameterized the RecursiveTask class with the List&lt;String&gt; type,</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//this method has to return an object of that type.</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">@Override</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">protected</code> 
      <code style="">List&lt;String&gt; compute()</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">{ </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//List to store the names of the files stored in the folder.</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">List&lt;String&gt; list =</code> 
      <code style="">new</code> 
      <code style="">ArrayList&lt;String&gt;();</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//FolderProcessor tasks to store the subtasks that are going to process the subfolders stored in the folder</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">List&lt;FolderProcessor&gt; tasks =</code> 
      <code style="">new</code> 
      <code style="">ArrayList&lt;FolderProcessor&gt;();</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//Get the content of the folder.</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">File file =</code> 
      <code style="">new</code> 
      <code style="">File(path);</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">File content[] = file.listFiles();</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//For each element in the folder, if there is a subfolder, create a new FolderProcessor object</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//and execute it asynchronously using the fork() method.</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">if</code> 
      <code style="">(content != </code> 
      <code style="">null</code> 
      <code style="">)</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">{ </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">for</code> 
      <code style="">(</code> 
      <code style="">int</code> 
      <code style="">i = </code> 
      <code style="">0</code> 
      <code style="">; i &lt; content.length; i++)</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">{ </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">if</code> 
      <code style="">(content[i].isDirectory())</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">{ </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">FolderProcessor task =</code> 
      <code style="">new</code> 
      <code style="">FolderProcessor(content[i].getAbsolutePath(), extension);</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">task.fork();</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">tasks.add(task);</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">}</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//Otherwise, compare the extension of the file with the extension you are looking for using the checkFile() method</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//and, if they are equal, store the full path of the file in the list of strings declared earlier.</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">else</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">{ </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">if</code> 
      <code style="">(checkFile(content[i].getName()))</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">{ </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">list.add(content[i].getAbsolutePath());</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">}</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">}</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">}</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">}</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//If the list of the FolderProcessor subtasks has more than 50 elements,</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//write a message to the console to indicate this circumstance.</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">if</code> 
      <code style="">(tasks.size() &gt; </code> 
      <code style="">50</code> 
      <code style="">)</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">{ </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">System.out.printf(</code> 
      <code style="">"%s: %d tasks ran.\n"</code> 
      <code style="">, file.getAbsolutePath(), tasks.size());</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">}</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//add to the list of files the results returned by the subtasks launched by this task.</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">addResultsFromTasks(list, tasks);</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//Return the list of strings</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">return</code> 
      <code style="">list;</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">}</code> 
     </div> 
     <div style="">
       &nbsp; 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//For each task stored in the list of tasks, call the join() method that will wait for its finalization and then will return the result of the task. </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//Add that result to the list of strings using the addAll() method.</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">private</code> 
      <code style="">void</code> 
      <code style="">addResultsFromTasks(List&lt;String&gt; list, List&lt;FolderProcessor&gt; tasks)</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">{ </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">for</code> 
      <code style="">(FolderProcessor item : tasks)</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">{ </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">list.addAll(item.join());</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">}</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">}</code> 
     </div> 
     <div style="">
       &nbsp; 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">//This method compares if the name of a file passed as a parameter ends with the extension you are looking for.</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">private</code> 
      <code style="">boolean</code> 
      <code style="">checkFile(String name)</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">{ </code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code> 
      <code style="">return</code> 
      <code style="">name.endsWith(extension);</code> 
     </div> 
     <div style=""> 
      <code style="">&nbsp;&nbsp;&nbsp;</code> 
      <code style="">}</code> 
     </div> 
     <div style=""> 
      <code style="">}</code> 
     </div> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

And to use above `FolderProcessor`, follow below code:

Main.java

Output of above program will look like this:

Main: Parallelism: 2
    Main: Active Threads: 3
    Main: Task Count: 1403
    Main: Steal Count: 5551
    ******************************************
    ******************************************
    Main: Parallelism: 2
    Main: Active Threads: 3
    Main: Task Count: 586
    Main: Steal Count: 5551
    ******************************************
    System: 337 files found.
    Apps: 10 files found.
    Documents: 0 files found.

### How it works? ###

In the `FolderProcessor` class, Each task processes the content of a folder. As you know, this content has the following two kinds of elements:

*  Files
 *  Other folders

If the task finds a folder, it creates another Task object to process that folder and sends it to the pool using the fork() method. This method sends the task to the pool that will execute it if it has a free worker-thread or it can create a new one. The method returns immediately, so the task can continue processing the content of the folder. For every file, a task compares its extension with the one it’s looking for and, if they are equal, adds the name of the file to the list of results.

Once the task has processed all the content of the assigned folder, it waits for the finalization of all the tasks it sent to the pool using the join() method. This method called in a task waits for the finalization of its execution and returns the value returned by thecompute() method. The task groups the results of all the tasks it sent with its own results and returns that list as a return value of the compute() method.

## Difference between Fork/Join Framework And ExecutorService ##

The main difference between the Fork/Join and the Executor frameworks is the work-stealing algorithm. Unlike the Executor framework, when a task is waiting for the finalization of the sub-tasks it has created using the join operation, the thread that is executing that task (called worker thread ) looks for other tasks that have not been executed yet and begins its execution. By this way, the threads take full advantage of their running time, thereby improving the performance of the application.

## Existing Implementations in JDK ##

There are some generally useful features in Java SE which are already implemented using the fork/join framework.

1) One such implementation, introduced in Java SE 8, is used by the java.util.Arrays class for its parallelSort() methods. These methods are similar to sort(), but leverage concurrency via the fork/join framework. Parallel sorting of large arrays is faster than sequential sorting when run on multiprocessor systems.

2) Parallelism used in Stream.parallel(). Read more about this [parallel stream operation in java 8][].

## Conclusion ##

Designing good multi-threaded algorithms is hard, and fork/join doesn’t work in every circumstance. It’s very useful within its own domain of applicability, but in the end, you have to decide whether your problem fits within the framework, and if not, you must be prepared to develop your own solution, building on the superb tools provided by java.util.concurrent package.

References

[http://gee.cs.oswego.edu/dl/papers/fj.pdf][http_gee.cs.oswego.edu_dl_papers_fj.pdf]  
[http://docs.oracle.com/javase/tutorial/essential/concurrency/forkjoin.html][Fork and Join framework]  
[http://www.packtpub.com/java-7-concurrency-cookbook/book][http_www.packtpub.com_java-7-concurrency-cookbook_book]

Happy Learning !!

[JAVA 7 FEATURES]: http://howtodoinjava.com/category/new-jdk-features/java-7-features/
[MULTI THREADING]: http://howtodoinjava.com/category/core-java/multi-threading/
[MAY 27_ 2014]: http://howtodoinjava.com/2014/05/27/forkjoin-framework-tutorial-forkjoinpool-example/
[LOKESH]: http://howtodoinjava.com/author/lokeshgupta1981/
[Link 1]: https://plus.google.com/111318583369754812286?rel=author
[2 COMMENTS]: http://howtodoinjava.com/2014/05/27/forkjoin-framework-tutorial-forkjoinpool-example/#comments
[Fork and Join framework]: http://docs.oracle.com/javase/tutorial/essential/concurrency/forkjoin.html
[divide-and-conquer algorithm]: http://en.wikipedia.org/wiki/Divide_and_conquer_algorithms
[work-stealing algorithm]: http://supertech.csail.mit.edu/papers/steal.pdf
[Fork Join Framework]: /images/20220810/6b53fb6051c94e0dae9c7a4de25c6a82.png
[parallel stream operation in java 8]: http://howtodoinjava.com/2014/04/13/java-8-tutorial-streams-by-examples/
[http_gee.cs.oswego.edu_dl_papers_fj.pdf]: http://gee.cs.oswego.edu/dl/papers/fj.pdf
[http_www.packtpub.com_java-7-concurrency-cookbook_book]: http://www.packtpub.com/java-7-concurrency-cookbook/book