Fork/Join框架

Fork/Join框架是Java 7提供的一個用於並行執行任務的框架，是一個把大任務分割成若干個小任務，最終彙總每個小任務結果後得到大任務結果的框架

package forkjoin;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.RecursiveTask;

public class CountTask extends RecursiveTask<Integer> {
    private static final int THRESHOLD = 2; // 閾值
    private int start;
    private int end;

    public CountTask(int start, int end) {
        this.start = start;
        this.end = end;
    }

    @Override
    protected Integer compute() {
        int sum = 0;
        // 如果任務足夠小就計算任務
        boolean canCompute = (end - start) <= THRESHOLD;
        if (canCompute) {
            for (int i = start; i <= end; i++) {
                sum += i;
            }
            return sum;
        } else {
            // 如果任務大於閾值，就分裂成兩個子任務計算
            int middle = (start + end) / 2;

            CountTask leftTask = new CountTask(start, middle);
            CountTask rightTask = new CountTask(middle + 1, end);

            leftTask.fork();
            rightTask.fork();

            int leftResult = leftTask.join();
            int rightResult = rightTask.join();

            sum = leftResult + rightResult;
        }
        return sum;
    }

    public static void main(String[] args) {
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        // 生成一個計算任務，負責計算1+2+3+4
        CountTask task = new CountTask(1, 4);
        // 執行一個任務
        Future<Integer> result = forkJoinPool.submit(task);
        try {
            System.out.println(result.get());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }

        if (task.isCompletedAbnormally()) {
            System.out.println("Abnormally task");
        }
    }
}