Fork-Join框架

package concurrent;
import java.util.ArrayList;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.RecursiveTask;
public class C04_ForkJoin {
    /**
     * .《实战JAVA高并发程序设计》P117——3.2.9分而治之：Fork/Join
     * Fork/Join框架是将大任务分解成小任务，通过合成子任务的子结果而得到结果。
     * ForkJoinPool线程池
     * ForkJoinTask-----RecurisiveTask  : 有返回值，通过 join()接收, 类似的接口有Callable
     *                --RecursiveAction : 没有返回值
     * .下面以计算数列前n项和为例子
     */
    public static class CountTask extends RecursiveTask<Long> {
        private static final int MAX = 10000;   //一个任务最多计算多少项的和
        private long start;
        private long end;
        public CountTask(long start, long end){ this.start = start; this.end = end; }
        @Override
        protected Long compute() {
            long sum = 0;
            boolean canCompute = (end - start) < MAX;
            if(canCompute){
                for(long i=start; i<=end; i++)
                    sum+=i;
            }else{
                //分成100个小任务
                ArrayList<CountTask> countTasks = new ArrayList<>(100);
                long step = (end - start) / 100;
                for(long i = start ; i<end ; i+= step + 1){
                    CountTask task = new CountTask(i, (i + step) < end ? (i + step) : end);
                    countTasks.add(task);
                    task.fork();    //执行
                }
                for(CountTask task : countTasks)
                    sum += task.join();
            }
            return sum;
        }
    }
    public static void main(String[] args){
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        CountTask task = new CountTask(0L, 500000L);
        ForkJoinTask<Long> result = forkJoinPool.submit(task);
        try{
            long res = result.get();    //获得结果
            System.out.println("result = " + res);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        }
        forkJoinPool.shutdown();
    }
}

console

result = 125000250000