JUC详解-14-ForkJoin详解

JUC详解 -> ForkJoin详解

什么是ForkJoin?

• JDK 1.7后
• 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操作

//求和计算的任务
import java.util.concurrent.RecursiveTask;

/**
 * 如何使用ForkJoin
 * 1.ForkJoinPool 通过它来执行
 * 2.计算任务forkjoin.execute(ForkJoinTask task)
 * 3.计算任务继承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;
        this.end = end;
    }
    @Override
    protected Long compute() {
        if((end - start)<temp){
            Long sum = 0L;
            for(Long i = start; i <= end; i++){
                sum = sum + i;
            }
            return sum;
        }else{
            //forkJoin分支合并计算
            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();
            return task1.join() + task2.join();
        }
    }
}

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

public class Test {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        //test1();
        //test2();
        test3();
    }

    public static void test1(){
        Long sum = 0L;
        long start = System.currentTimeMillis();
        for (Long i = 1L; i < 10_0000_0000; i++) {
            sum = sum + i;
        }
        long end = System.currentTimeMillis();
        System.out.println("sum= " + "时间："+ (end - start));  //9949
    }

    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= " + "时间："+ (end - start)); //4055
    }

    public static void test3(){
        long start = System.currentTimeMillis();
        //Stream
        long sum = LongStream.rangeClosed(1L, 10_0000_0000).parallel().reduce(0, Long::sum); //368

        long end = System.currentTimeMillis();
        System.out.println("sum= " + "时间："+ (end - start));
    }
}

System.currentTimeMillis();
System.out.println("sum= " + “时间：”+ (end - start));
}
}