What's New in Java 7

Fork and Join

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.

The core classes supporting the Fork-Join mechanism are ForkJoinPool and ForkJoinTask. 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 — the number of processors as shown below:

ForkJoinPool pool = new ForkJoinPool(numberOfProcessors)

Where numberOfProcessors = Runtime.getRunTime().availableProcessors();

However, the default ForkJoinPool instantiation would set the parallelism level equal to the same number obtained as above.

The problem that needs to be solved is coded in a ForkJoinTask. However, there are two implementations of this class out of the box: the RecursiveAction and RecursiveTask. The only difference between these two classes ...