java并发框架--Fork-Join

并行计算

Fork-Join

关键类

例子

```
package sumTest2;
/**
* 计算1-10000000的和
* 适用范围：计算不知道计算量大小的计算
*/
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;

public class SumTest {

public static void main(String[] args) throws ExecutionException, InterruptedException {

ForkJoinPool pool = new ForkJoinPool();

    SumTask task = new SumTask(1,10000000);//大任务
    ForkJoinTask<Long> result = pool.submit(task);
    //等待结果
    do {
        System.out.printf("Main: Thread Count: %d\n",pool.getActiveThreadCount());//正在运行的线程
        System.out.printf("Main: Paralelism: %d\n",pool.getParallelism());//并行度
        try {
            Thread.sleep(50);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    } while (!task.isDone());
    System.out.println(result.get().toString());
}

}

```java
package sumTest2;
import java.util.concurrent.RecursiveTask;
//继承这个可以自动递归
public class SumTask extends RecursiveTask<Long> {
    private int start;
    private int end;
    public SumTask(int start, int end) {
        this.start = start;
        this.end = end;
    }
    public static final int  Max= 5;
    @Override
    protected Long compute() {
        Long sum = 0L;
        boolean canCompute = (end - start)<= Max;
        if (canCompute){
            for (int i = start; i <= end; i++){
                sum += i;
            }
        }else{
            int middle = (end + start) / 2;
            SumTask subTask1 = new SumTask(start, middle);
            SumTask subTask2 = new SumTask(middle+1, end);
            //invokeAll(subTask1, subTask2);
            subTask1.fork();
            subTask2.fork();
            Long sum1 = subTask1.join();
            Long sum2 = subTask2.join();
            sum = sum1 + sum2;
        }
        return sum;
    }
}