ForkJion

ForkJoin

什么是ForkJoin

ForkJion 在JDK1.7,并行执行任务！提高效率。大数据量！

大数据：Map Reduce(将大任务拆分为小任务)

ForkJion 特点：工作窃取
这个里面维护的都是双端队列，A 线程没有执行完，B线程执行完了，B 线程则去 执行A 中的（红框）未执行完任务

ForkJion

代码案例：

package com.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)
*/
public class Test {


public static void main(String[] args) throws ExecutionException, InterruptedException {
//test1();//8039
//test2(); //4369
test3(); //152
    }

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));
      }

public  static  void  test2() throws ExecutionException, InterruptedException {
Long sum =0L;
long start = System.currentTimeMillis();
//forkJoin 池子
ForkJoinPool forkJoinPool = new ForkJoinPool();
//实例化业务方法
ForkJoinTask<Long> task = new ForkJoinDemo(0L,10_0000_0000L);

//在池子中执行业务
ForkJoinTask<Long> submit = forkJoinPool.submit(task);

sum = submit.get();

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

public  static  void  test3() throws ExecutionException, InterruptedException {
Long sum =0L;
long start = System.currentTimeMillis();
//Stream  并行流 range 不包含后面的,rangeClosed 包含后面的
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));
    }

}

package com.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forkjoinPoolexecute
* 3.计算类要继承ForkJoinTask
*
* Recursive : 发音 rekusive
*
*/
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;
    }

public static void main(String[] args) {
//        int sum =0;
//        for (int i = 0; i < 10_0000_0000; i++) {
//            sum+=i;
//        }
//        System.out.println(sum);
//
//

       }

public void test(){
//100 -50 >50
if((end -start) >temp){
int sum =0;
for (int i = 0; i < 10_0000_0000; i++) {
sum+=i;
            }
System.out.println(sum);
        }
       }

//计算的返回值就是 RecursiveTask 的泛型
@Override
protected Long compute() {
//如果范围比 1 万还小我们就不用分支合并
if((end -start) <temp){
Long sum =0L;
for (long i =start; i <=end; i++) {
sum+=i;
            }
return sum;
        }else{ //forkjoin: 一个任务拆分为多个任务 ,像递归
long middle = (start + end) / 2; //中间值
ForkJoinDemo task1 = new ForkJoinDemo(start, middle);
task1.fork(); //拆分任务,把任务压入到线程队列


ForkJoinDemo task2 = new ForkJoinDemo(middle+1, end);
task2.fork();
return task1.join() + task2 .join();
        }
    }
}