详解Java中的ForkJoin

package com.fandf.test.forkjoin;  
  
import lombok.extern.slf4j.Slf4j;  
import org.springframework.util.StopWatch;  
  
import java.util.concurrent.ForkJoinPool;  
import java.util.concurrent.Future;  
import java.util.concurrent.RecursiveTask;  
  
/**  
* @author fandongfeng  
*/  
@Slf4j  
public class ForkJoinDemo extends RecursiveTask<Long> {  
  
    /**  
    * 小任务的大小阈值  
    */  
    public static final int TASK_SIZE = 100000;  
    /**  
    * 开始数字  
    */  
    private final Long start;  
    /**  
    * 结束数字  
    */  
    private final Long end;  

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

    @Override  
    protected Long compute() {  
        long sum = 0L;  
        //如果任务足够小就计算任务  
        boolean canCompute = (end - start) <= TASK_SIZE;  
        if (canCompute) {  
            for (Long i = start; i <= end; i++) {  
                sum += i;  
            }  
        } else {  
            // 如果任务大于阈值，就分裂成两个子任务计算  
            long middle = (start + end) / 2;  
            ForkJoinDemo leftTask = new ForkJoinDemo(start, middle);  
            ForkJoinDemo rightTask = new ForkJoinDemo(middle + 1, end);  

            // 执行子任务  
            leftTask.fork();  
            rightTask.fork();  

            // 等待任务执行结束合并其结果  
            Long leftResult = leftTask.join();  
            Long rightResult = rightTask.join();  

            // 合并子任务  
            sum = leftResult + rightResult;  
        }  
        return sum;  
    }  

    public static void main(String[] args) {  
        ForkJoinPool forkjoinPool = new ForkJoinPool();  
        //生成一个计算任务，计算1+2+3+4+...+100000000  
        ForkJoinDemo task = new ForkJoinDemo(1L, 100000000L);  
        StopWatch stopWatch = new StopWatch();  
        stopWatch.start();  
        //执行一个任务  
        Future<Long> result = forkjoinPool.submit(task);  

        try {  
            System.out.println("result:" + result.get());  
        } catch (Exception e) {  
            log.error("exception", e);  
        }  
        stopWatch.stop();  
        System.out.println("总耗时：" + stopWatch.getTotalTimeMillis() + "毫秒");  
        System.out.println("getParallelism:" + forkjoinPool.getParallelism());  
        System.out.println("getPoolSize:" + forkjoinPool.getPoolSize());  
    }  
}

public ForkJoinPool() {  
    this(Math.min(MAX_CAP, Runtime.getRuntime().availableProcessors()),  
        defaultForkJoinWorkerThreadFactory, null, false);  
}

public ForkJoinPool(int parallelism,  
                    ForkJoinWorkerThreadFactory factory,  
                    UncaughtExceptionHandler handler,  
                    boolean asyncMode) {  
    this(checkParallelism(parallelism),  
        checkFactory(factory),  
        handler,  
        asyncMode ? FIFO_QUEUE : LIFO_QUEUE,  
        "ForkJoinPool-" + nextPoolId() + "-worker-");  
    checkPermission();  
}