forkJoin的使用，分支合併

如何使用forkJoin
1、forkJoinPool 通過他來執行
2、計算任務 forkJoinPool.execute(ForkJoinTask task)
3、計算要繼承forkJoinTask

package ForkJoinA;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.stream.LongStream;

/**分支合併 ForkJoin
 * @author liu
 */
public class Test {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        //test1();//結果：500000000500000000 時間：4841
        //test2();//500000000500000000 時間：7876
test3();
    }

    public static void test1() {
        Long sum = 0L;
        long start = System.currentTimeMillis();
        for (int i = 1; i <= 10_0000_0000; i++) {
            sum += i;
        }
        long end = System.currentTimeMillis();
        System.out.println("結果：" + sum + " 時間：" + (end - start));
    }

    public static void test2() throws ExecutionException, InterruptedException {
        long start = System.currentTimeMillis();

        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Long> task = new Demo01(0L, 10_0000_0000L);
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);//提交任務
        Long sum = submit.get();
        long end = System.currentTimeMillis();
        System.out.println("結果：" + sum + " 時間：" + (end - start));
    }

    public static void test3() {
        long start = System.currentTimeMillis();
        //stream並行流  range併發是（） rangeClose是（ ]  reduce減少
        Long sum = LongStream.rangeClosed(0L, 10_0000_0000L).parallel().reduce(0L,Long::sum);
        long end = System.currentTimeMillis();
        System.out.println("結果：" + sum + " 時間：" + (end - start));
    }
}
 

extends RecursiveTask ，重寫compute

package ForkJoinA;

import java.util.concurrent.RecursiveTask;

/**
 * 如何使用forkJoin
 * 1、forkJoinPool  通過他來執行
 * 2、計算任務 forkJoinPool.execute(ForkJoinTask task)
 * 3、計算要繼承forkJoinTask
 *
 * @author liu
 */
public class Demo01 extends RecursiveTask<Long> {
    private Long start;
    private Long end;

    //臨界值
    private Long temp = 10000L;

    public Demo01(Long start, Long end) {
        this.start = start;
        this.end = end;
    }

    //計算方法
    @Override
    protected Long compute() {
        if ((end - start) < temp) {
            Long sum = 0L;
            for (Long i = start; i < end + 1; i++) {
                sum = sum + i;
            }
            return sum;
        } else {//forkJoin 遞迴
            Long mid=(start+end)/2;
            Demo01 task1=new Demo01(start,mid);
            task1.fork();//拆分任務，把任務壓入執行緒佇列
            Demo01 task2=new Demo01(mid+1,end);
            task2.fork();//拆分任務，把任務壓入執行緒佇列
            return task1.join()+task2.join();
        }

    }
}