ForkJoin

ForkJoin

分支合并

什么是ForkJoin

ForkJoin在JDK1.7，并行执行任务！提高效率，大数据量！

大数据：Map Reduce (把大任务拆分为小任务)

ForkJoin 特点：工作窃取

这个里面维护的都是双端队列

ForkJoin

package com.chao.forkjoin;
import java.util.concurrent.RecursiveTask;
/**
 * 求和计算的任务！
 * 3000 6000(ForkJoin) 9000(Stream并行流)
 * //如何使用 forkjoin
 * // 1、forkjoinPool 通过它来执行
 * // 2、计算任务forkjoinPool.execute(ForkJoinTask task)
 * // 3、计算类要继承 ForkJoinTask
 *
 */
public class ForkJoinDemo extends RecursiveTask<Long> {
    private Long start;
    private Long end;
    //临界值
    private Long temp = 10000L;

    public ForkJoinDemo(Long start, Long end) {
        this.start = start;  // 1
        this.end = end;      // 1990900000
    }

    /*    public void test(){
    //    public static void main(String[] args) {
    //        int sum = 0;
    //        for (int i = 1; i <10_0000_0000 ; i++) {
    //            sum += i;
    //        }
    //        System.out.println(sum);
            if((end-start)>temp){
                // 分支合并计算
            }else{
                int sum = 0;
                for (int i = 1; i <10_0000_0000 ; i++) {
                    sum += i;
                }
                System.out.println(sum);
            }
        }*/
    //计算方法
    @Override
    protected Long compute() {
        if ((end - start) < temp) {
            Long sum = 0L;
            for (Long i = start; i < end; i++) {
                sum += i;
            }
            return sum;
        } else { // forkjoin  递归
            long middle = (start + end) / 2; //中间值
            ForkJoinDemo task1 = new ForkJoinDemo(start, middle);
            task1.fork();//拆分任务，把任务压入线程队列
            ForkJoinDemo task2 = new ForkJoinDemo(middle+1, end);
            task2.fork();//拆分任务，把任务压入线程队列
            return task1.join() + task2.join();
        }
    }
}

测试：

package com.chao.forkjoin;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.stream.LongStream;
// 3000 6000(ForkJoin) 9000(Stream并行流)
/**
 *同一个任务,别人效率高你几十倍！
 */
public class Test {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        //test1(); //5137
        //test2(); //3607
        test3(); //129
    }
    //普通程序员
    public  static void test1(){
        Long sum = 0L;
        long start = System.currentTimeMillis();

        for (Long i = 1L; i < 10_0000_0000; i++) {
            sum += i;
        }
        long end = System.currentTimeMillis();
        System.out.println("sum="+sum+" 时间："+(end-start));
    }
    //会使用ForkJoin
    public  static void test2() throws ExecutionException, InterruptedException {
        long start = System.currentTimeMillis();
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Long> task = new ForkJoinDemo(0L,10_0000_0000L);
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);//提交任务
        Long sum = submit.get();
        long end = System.currentTimeMillis();
        System.out.println("sum="+sum+" 时间："+(end-start));
    }

    //Stream并行流
    public  static void test3(){
        long start = System.currentTimeMillis();
        //range  ()  rangClosed (]
        long sum = LongStream.rangeClosed(0L, 10_0000_0000L).parallel().reduce(0, Long::sum);
        long end = System.currentTimeMillis();
        System.out.println("sum="+sum+" 时间："+(end-start));
    }
}