【并发编程】- 线程池执行任务乱序特性

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线程池ThreadPoolExecutor执行任务Runnable乱序特性

接口Runnable在线程池ThreadPoolExecutor的队列中是按顺序取出，执行却是乱序的。

线程执行代码如下：

@Slf4j
public class TheRunnable implements Runnable {

    private String username;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public TheRunnable(String username){
        super();
        this.username=username;
    }



    @Override
    public void run() {
        try {
            Thread.sleep(2000);
            log.info("线程名："+username);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

运行类代码如下：

public class DisorderedOrderRun {
    public static void main(String[] args) {
        ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(5, 10, 10, TimeUnit.SECONDS, new LinkedBlockingQueue<>());
        for (int i = 0; i < 20; i++) {
            TheRunnable theRunnable = new TheRunnable("G" + (i + 1));
            threadPoolExecutor.execute(theRunnable);
        }
    }
}

运行结果如下：

10:37:06.675 [pool-1-thread-5] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G5 10:37:06.660 [pool-1-thread-3] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G3 10:37:06.675 [pool-1-thread-1] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G1 10:37:06.660 [pool-1-thread-2] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G2 10:37:06.706 [pool-1-thread-4] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G4 10:37:08.692 [pool-1-thread-3] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G6 10:37:08.692 [pool-1-thread-1] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G7 10:37:08.692 [pool-1-thread-5] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G8 10:37:08.692 [pool-1-thread-2] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G9 10:37:08.723 [pool-1-thread-4] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G10 10:37:10.708 [pool-1-thread-3] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G11 10:37:10.708 [pool-1-thread-1] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G12 10:37:10.708 [pool-1-thread-5] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G13 10:37:10.708 [pool-1-thread-2] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G14 10:37:10.739 [pool-1-thread-4] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G15 10:37:12.714 [pool-1-thread-1] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G17 10:37:12.714 [pool-1-thread-3] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G16 10:37:12.714 [pool-1-thread-5] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G18 10:37:12.714 [pool-1-thread-2] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G19 10:37:12.745 [pool-1-thread-4] INFO com.ozx.concurrentprogram.executor.service.TheRunnable - 线程名：G20

从运行结果看出Runnable状态从就绪态到运行态转换，线程各自获取CPU时间片不一样，所以线程执行顺序是乱序的。

通过使用线程池能最大幅度地减少创建线程对象的内存与CPU开销，加快程序运行效率，进而对创建线程类的代码进行了封装。