Concurrent Java 05 - JUC组件扩展

Callable和Runnable

Callable和Runnable的区别在于前者执行线程任务后是可以返回值。

package com.accat.concurrency.example.aqs;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

@Slf4j
public class FutureExample {

    static class MyCallable implements Callable<String> {

        @Override
        public String call() throws Exception {
            log.info("do something in callable");
            Thread.sleep(5000);
            return "Done";
        }
    }

    public static void main(String[] args) throws Exception {
        ExecutorService executorService = Executors.newCachedThreadPool();
        Future<String> future = executorService.submit(new MyCallable());
        log.info("do something in main");
        Thread.sleep(1000);
        String result = future.get();
        log.info("result：{}", result);
    }
}

FutureTask

FutureTask和Callable关系相当于Thread和Runnable的关系
前者支持返回值提取和状态获取。

package com.accat.concurrency.example.aqs;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;

@Slf4j
public class FutureTaskExample {

    public static void main(String[] args) throws Exception {
        FutureTask<String> futureTask = new FutureTask<>(() -> {
            log.info("do something in callable");
            Thread.sleep(5000);
            return "Done";
        });

        new Thread(futureTask).start();
        log.info("do something in main");
        Thread.sleep(1000);
        log.info("waiting result");
        String result = futureTask.get(); // 阻塞并获取结果
        log.info("result：{}", result);
    }
}

Fork/Join 框架

Fork切分大任务， 得出小结果集；
Join合并小结果集，得出最终结果；
采用工作窃取算法，避免线程竞争。

工作窃取算法，当线程工作完后去窃取其他任务来进行执行

package com.accat.concurrency.example.aqs;

import lombok.extern.slf4j.Slf4j;

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.RecursiveTask;

@Slf4j
public class ForkJoinTaskExample extends RecursiveTask<Integer> {

    public static final int threshold = 2;
    private int start;
    private int end;

    public ForkJoinTaskExample(int start, int end) {
        this.start = start;
        this.end = end;
    }

    @Override
    protected Integer compute() {
        int sum = 0;

        //如果任务足够小就计算任务
        boolean canCompute = (end - start) <= threshold;
        if (canCompute) {
            for (int 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
            int middle = (start + end) / 2;
            ForkJoinTaskExample leftTask = new ForkJoinTaskExample(start, middle);
            ForkJoinTaskExample rightTask = new ForkJoinTaskExample(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
            int leftResult = leftTask.join();
            int 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
        ForkJoinTaskExample task = new ForkJoinTaskExample(1, 100);

        //执行一个任务
        Future<Integer> result = forkjoinPool.submit(task);

        try {
            log.info("result:{}", result.get());
        } catch (Exception e) {
            log.error("exception", e);
        }
    }
}

AQS组件 - BlockingQueue

阻塞队列 提供的四套方法，当操作无法进行则做出相应的操作

ArrayBlockingQueue 有界数组实现的阻塞队列
DelayQueue 使用PriorityQueue优先队列和ReentrantLock锁实现的延迟队列
LinkedBlockingDeque 双端链表实现的阻塞队列
PriorityBlockingQueue 无界可排序的阻塞队列
SynchronousQueue 内部仅支持一个元素存取的同步队列