【并发编程】- 线程池执行任务乱序特性

ゞ浴缸里的玫瑰 2023-09-27 16:01 157阅读 0赞

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。