A guide to using the Fork/Join framework in Java parallel programming

Java Fork/Join Framework Guide: Create Fork/Join tasks: Use the RecursiveAction (no return value) or RecursiveTask (with return value) class extension to implement the compute method. Create a Fork/Join pool: Use ForkJoinPool to specify the number of threads. Submit the task: Use fork() to submit the task and join() to wait for the result. Decompose the task: call fork() and join() in the compute method to decompose the task. Practical case (quick sort): Create a QuickSortTask task and submit it to ForkJoinPool for execution.

Guidelines for the use of the Fork/Join framework in Java parallel programming

The Fork/Join framework is used in the Java parallel programming model Advanced methods for task parallelization. It adopts a divide-and-conquer strategy, decomposing tasks into subtasks, then executing them in parallel, and finally merging the results. This guide will introduce how to use the Fork/Join framework and demonstrate it through a practical case.

Creating Fork/Join tasks

The basis of the Fork/Join framework is the RecursiveAction and RecursiveTask classes.

• RecursiveAction Used for tasks that have no return value.
• RecursiveTask For tasks with return values.

To create tasks, you need to extend these two classes and implement the compute method. compute The method is the code for task execution.

Create a Fork/Join pool

The Fork/Join framework uses the ForkJoinPool object to manage the execution of tasks. It is a thread pool used for scheduling and executing tasks. When creating a pool, you can specify the number of threads.

ForkJoinPool pool = new ForkJoinPool(Runtime.getRuntime().availableProcessors());

Submit a task

To submit a task, use the fork() and join() methods. The fork() method submits the task to the pool, while the join() method waits for the task to complete and returns the result (for RecursiveTask tasks).

pool.fork(task);
long result = pool.join();

Decompose tasks

For large tasks, you can break them down into smaller subtasks. To do this, the fork() and join() methods can be called within the compute method.

@Override
protected void compute() {
  if (problem.isTooBig()) {
    ForkJoinTask leftTask = new LeftTask(leftHalf);
    ForkJoinTask rightTask = new RightTask(rightHalf);
    leftTask.fork();
    rightTask.fork();
    leftTask.join();
    rightTask.join();
  } else {
    // solve the problem directly
  }
}

Practical case: Quick sort

The following is an example of the quick sort algorithm using the Fork/Join framework:

public class QuickSortTask extends RecursiveTask<long[]> {

  private int[] array;
  private int low;
  private int high;

  public QuickSortTask(int[] array, int low, int high) {
    this.array = array;
    this.low = low;
    this.high = high;
  }

  @Override
  protected long[] compute() {
    if (low < high) {
      int pivot = partition(array, low, high);
      ForkJoinTask leftTask = new QuickSortTask(array, low, pivot - 1);
      ForkJoinTask rightTask = new QuickSortTask(array, pivot + 1, high);
      leftTask.fork();
      rightTask.fork();
      leftTask.join();
      rightTask.join();
    }
    return array;
  }

  private int partition(int[] array, int low, int high) {
    // ...
  }

}

To use this algorithm, Please create a QuickSortTask object and submit it to ForkJoinPool:

ForkJoinPool pool = new ForkJoinPool();
int[] array = {5, 3, 8, 2, 1, 4};
QuickSortTask task = new QuickSortTask(array, 0, array.length - 1);
pool.invoke(task);

Conclusion

The Fork/Join framework provides A simple and easy way to parallelize tasks in Java. Through a divide-and-conquer strategy, large tasks can be efficiently broken down and executed in parallel. Parallel tasks can be easily created and managed by using the RecursiveAction and RecursiveTask classes, along with the ForkJoinPool.

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