• ThreadPoolExecutor执行过程分析


    ThreadPoolExecutor

    public ThreadPoolExecutor(int corePoolSize,
                                  int maximumPoolSize,
                                  long keepAliveTime,
                                  TimeUnit unit,
                                  BlockingQueue<Runnable> workQueue,
                                  ThreadFactory threadFactory,
                                  RejectedExecutionHandler handler)
    • corePoolSize:线程池核心线程数(平时保留的线程数)
    • maximumPoolSize:线程池最大线程数(当workQueue都放不下时,启动新线程,最大线程数)
    • keepAliveTime:超出corePoolSize数量的线程的保留时间。
    • unit:keepAliveTime单位
    • workQueue:阻塞队列,存放来不及执行的线程

      • ArrayBlockingQueue:构造函数一定要传大小
      • LinkedBlockingQueue:构造函数不传大小会默认为65536(Integer.MAX_VALUE ),当大量请求任务时,容易造成 内存耗尽。
      • SynchronousQueue:同步队列,一个没有存储空间的阻塞队列 ,将任务同步交付给工作线程。
      • PriorityBlockingQueue : 优先队列
    • threadFactory:线程工厂
    • handler:饱和策略

      • AbortPolicy(默认):直接抛弃
      • CallerRunsPolicy:用调用者的线程执行任务
      • DiscardOldestPolicy:抛弃队列中最久的任务
      • DiscardPolicy:抛弃当前任务

    ThreadPoolExecutor 测试代码

    //test.java
    volatile int finishState = 0;
    
    
    @Test
    public void test4() throws InterruptedException, ExecutionException {
       ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(3, 7, 10, TimeUnit.SECONDS, new LinkedBlockingDeque<>(10));
       ExecutorCompletionService<String> executorCompletionService = new ExecutorCompletionService(threadPoolExecutor);
    
       Runnable runnable = new Runnable() {
          @Override
          public void run() {
             for (int i = 0; i < 50; i++) {
                String name = "name_" + i;
                TestCallable testCallable = new TestCallable(name);
                try {
                   executorCompletionService.submit(testCallable);
    
                   synchronized (lock) {
                      System.out.print("+++添加任务 name: " + name);
                      System.out.print(" ActiveCount: " + threadPoolExecutor.getActiveCount());
                      System.out.print(" poolSize: " + threadPoolExecutor.getPoolSize());
                      System.out.print(" queueSize: " + threadPoolExecutor.getQueue().size());
                      System.out.println(" taskCount: " + threadPoolExecutor.getTaskCount());
                   }
                } catch (RejectedExecutionException e) {
                   synchronized (lock) {
                      System.out.println("拒绝:" + name);
                   }
                }
                try {
                   Thread.sleep(200);
                } catch (InterruptedException e) {
                   e.printStackTrace();
                }
             }
             finishState = 1;
          }
       };
    
       Thread addThread = new Thread(runnable);
       addThread.start();
    
       //System.out.println(" taskCount: " + threadPoolExecutor.getTaskCount());
    
       //添加的任务有被抛弃的。taskCount不一定等于添加的任务。
       int completeCount = 0;
       while (!(completeCount == threadPoolExecutor.getTaskCount() && finishState == 1)) {
          Future<String> take = executorCompletionService.take();
          String taskName = take.get();
          synchronized (lock) {
             System.out.print("---完成任务 name: " + taskName);
             System.out.print(" ActiveCount: " + threadPoolExecutor.getActiveCount());
             System.out.print(" poolSize: " + threadPoolExecutor.getPoolSize());
             System.out.print(" queueSize: " + threadPoolExecutor.getQueue().size());
             System.out.print(" taskCount: " + threadPoolExecutor.getTaskCount());
             System.out.println(" finishTask:" + (++completeCount));
    
          }
       }
    
       addThread.join();
    
    
       while (threadPoolExecutor.getPoolSize() > 0) {
          Thread.sleep(1000);
          synchronized (lock) {
             SimpleDateFormat simpleDateFormat = new SimpleDateFormat("HH:mm:ss");
             System.out.print(simpleDateFormat.format(new Date()));
             //System.out.print("name: " + taskName);
             System.out.print(" ActiveCount: " + threadPoolExecutor.getActiveCount());
             System.out.print(" poolSize: " + threadPoolExecutor.getPoolSize());
             System.out.print(" queueSize: " + threadPoolExecutor.getQueue().size());
             System.out.println(" taskCount: " + threadPoolExecutor.getTaskCount());
          }
       }
    
       // Tell threads to finish off.
       threadPoolExecutor.shutdown();
       // Wait for everything to finish.
       while (!threadPoolExecutor.awaitTermination(10, TimeUnit.SECONDS)) {
          System.out.println("complete");
       }
    
    }
    //TestCallable.java
    public class TestCallable implements Callable<String>{
    
    
       private String name;
    
       public TestCallable(String name) {
          this.name = name;
       }
    
       @Override
       public String call() throws Exception {
          try {
             Thread.sleep(2000);
          } catch (InterruptedException e) {
             e.printStackTrace();
          }
          return this.name;
       }
    }

    执行结果

    +++添加任务 name: name_0 ActiveCount: 1 poolSize: 1 queueSize: 0 taskCount: 1
    +++添加任务 name: name_1 ActiveCount: 2 poolSize: 2 queueSize: 0 taskCount: 2
    +++添加任务 name: name_2 ActiveCount: 3 poolSize: 3 queueSize: 0 taskCount: 3
    //corePoolSize=3,所以poolSize逐渐加到3.
    +++添加任务 name: name_3 ActiveCount: 3 poolSize: 3 queueSize: 1 taskCount: 4
    +++添加任务 name: name_4 ActiveCount: 3 poolSize: 3 queueSize: 2 taskCount: 5
    +++添加任务 name: name_5 ActiveCount: 3 poolSize: 3 queueSize: 3 taskCount: 6
    +++添加任务 name: name_6 ActiveCount: 3 poolSize: 3 queueSize: 4 taskCount: 7
    +++添加任务 name: name_7 ActiveCount: 3 poolSize: 3 queueSize: 5 taskCount: 8
    +++添加任务 name: name_8 ActiveCount: 3 poolSize: 3 queueSize: 6 taskCount: 9
    +++添加任务 name: name_9 ActiveCount: 3 poolSize: 3 queueSize: 7 taskCount: 10
    ---完成任务 name: name_0 ActiveCount: 3 poolSize: 3 queueSize: 6 taskCount: 10 finishTask:1
    +++添加任务 name: name_10 ActiveCount: 3 poolSize: 3 queueSize: 7 taskCount: 11
    ---完成任务 name: name_1 ActiveCount: 3 poolSize: 3 queueSize: 6 taskCount: 11 finishTask:2
    +++添加任务 name: name_11 ActiveCount: 3 poolSize: 3 queueSize: 7 taskCount: 12
    ---完成任务 name: name_2 ActiveCount: 3 poolSize: 3 queueSize: 6 taskCount: 12 finishTask:3
    +++添加任务 name: name_12 ActiveCount: 3 poolSize: 3 queueSize: 7 taskCount: 13
    +++添加任务 name: name_13 ActiveCount: 3 poolSize: 3 queueSize: 8 taskCount: 14
    +++添加任务 name: name_14 ActiveCount: 3 poolSize: 3 queueSize: 9 taskCount: 15
    +++添加任务 name: name_15 ActiveCount: 3 poolSize: 3 queueSize: 10 taskCount: 16
    //因为任务队列为:new LinkedBlockingDeque<>(10),core线程不够用时,将任务添加到队列中。
    //queueSize到10,队列已满。开始增加poolSize,加到maximumPoolSize=7
    +++添加任务 name: name_16 ActiveCount: 4 poolSize: 4 queueSize: 10 taskCount: 17
    +++添加任务 name: name_17 ActiveCount: 5 poolSize: 5 queueSize: 10 taskCount: 18
    +++添加任务 name: name_18 ActiveCount: 6 poolSize: 6 queueSize: 10 taskCount: 19
    +++添加任务 name: name_19 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 20
    ---完成任务 name: name_3 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 20 finishTask:4
    +++添加任务 name: name_20 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 21
    ---完成任务 name: name_4 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 21 finishTask:5
    +++添加任务 name: name_21 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 22
    ---完成任务 name: name_5 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 22 finishTask:6
    +++添加任务 name: name_22 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 23
    //poolSize=maximumPoolSize,queueSize=10,都满了。执行饱和策略。默认AbortPolicy抛弃新任务。
    拒绝:name_23
    拒绝:name_24
    拒绝:name_25
    ---完成任务 name: name_16 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 23 finishTask:7
    +++添加任务 name: name_26 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 24
    ---完成任务 name: name_17 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 24 finishTask:8
    +++添加任务 name: name_27 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 25
    ---完成任务 name: name_18 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 25 finishTask:9
    +++添加任务 name: name_28 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 26
    ---完成任务 name: name_19 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 26 finishTask:10
    +++添加任务 name: name_29 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 27
    ---完成任务 name: name_6 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 27 finishTask:11
    +++添加任务 name: name_30 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 28
    ---完成任务 name: name_7 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 28 finishTask:12
    +++添加任务 name: name_31 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 29
    ---完成任务 name: name_8 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 29 finishTask:13
    +++添加任务 name: name_32 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 30
    拒绝:name_33
    拒绝:name_34
    拒绝:name_35
    ---完成任务 name: name_9 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 30 finishTask:14
    +++添加任务 name: name_36 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 31
    ---完成任务 name: name_10 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 31 finishTask:15
    +++添加任务 name: name_37 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 32
    ---完成任务 name: name_11 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 32 finishTask:16
    +++添加任务 name: name_38 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 33
    ---完成任务 name: name_12 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 33 finishTask:17
    +++添加任务 name: name_39 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 34
    ---完成任务 name: name_13 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 34 finishTask:18
    +++添加任务 name: name_40 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 35
    ---完成任务 name: name_14 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 35 finishTask:19
    +++添加任务 name: name_41 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 36
    ---完成任务 name: name_15 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 36 finishTask:20
    +++添加任务 name: name_42 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 37
    拒绝:name_43
    拒绝:name_44
    拒绝:name_45
    ---完成任务 name: name_20 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 37 finishTask:21
    +++添加任务 name: name_46 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 38
    ---完成任务 name: name_21 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 38 finishTask:22
    +++添加任务 name: name_47 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 39
    ---完成任务 name: name_22 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 39 finishTask:23
    //消费速度大于添加速度,poolSize并不减少,先把queue中的任务逐一执行完成。
    +++添加任务 name: name_48 ActiveCount: 7 poolSize: 7 queueSize: 10 taskCount: 40
    ---完成任务 name: name_26 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 40 finishTask:24
    ---完成任务 name: name_27 ActiveCount: 7 poolSize: 7 queueSize: 8 taskCount: 40 finishTask:25
    +++添加任务 name: name_49 ActiveCount: 7 poolSize: 7 queueSize: 9 taskCount: 41
    ---完成任务 name: name_28 ActiveCount: 7 poolSize: 7 queueSize: 8 taskCount: 41 finishTask:26
    ---完成任务 name: name_29 ActiveCount: 7 poolSize: 7 queueSize: 7 taskCount: 41 finishTask:27
    ---完成任务 name: name_30 ActiveCount: 7 poolSize: 7 queueSize: 6 taskCount: 41 finishTask:28
    ---完成任务 name: name_31 ActiveCount: 7 poolSize: 7 queueSize: 5 taskCount: 41 finishTask:29
    ---完成任务 name: name_32 ActiveCount: 7 poolSize: 7 queueSize: 4 taskCount: 41 finishTask:30
    ---完成任务 name: name_36 ActiveCount: 7 poolSize: 7 queueSize: 3 taskCount: 41 finishTask:31
    ---完成任务 name: name_37 ActiveCount: 7 poolSize: 7 queueSize: 2 taskCount: 41 finishTask:32
    ---完成任务 name: name_38 ActiveCount: 7 poolSize: 7 queueSize: 1 taskCount: 41 finishTask:33
    ---完成任务 name: name_39 ActiveCount: 7 poolSize: 7 queueSize: 0 taskCount: 41 finishTask:34
    //ActiveCount开始减少。
    ---完成任务 name: name_40 ActiveCount: 6 poolSize: 7 queueSize: 0 taskCount: 41 finishTask:35
    ---完成任务 name: name_41 ActiveCount: 5 poolSize: 7 queueSize: 0 taskCount: 41 finishTask:36
    ---完成任务 name: name_42 ActiveCount: 4 poolSize: 7 queueSize: 0 taskCount: 41 finishTask:37
    ---完成任务 name: name_46 ActiveCount: 3 poolSize: 7 queueSize: 0 taskCount: 41 finishTask:38
    ---完成任务 name: name_47 ActiveCount: 2 poolSize: 7 queueSize: 0 taskCount: 41 finishTask:39
    ---完成任务 name: name_48 ActiveCount: 1 poolSize: 7 queueSize: 0 taskCount: 41 finishTask:40
    ---完成任务 name: name_49 ActiveCount: 0 poolSize: 7 queueSize: 0 taskCount: 41 finishTask:41
    22:47:49 ActiveCount: 0 poolSize: 7 queueSize: 0 taskCount: 41
    22:47:50 ActiveCount: 0 poolSize: 7 queueSize: 0 taskCount: 41
    22:47:51 ActiveCount: 0 poolSize: 7 queueSize: 0 taskCount: 41
    22:47:52 ActiveCount: 0 poolSize: 7 queueSize: 0 taskCount: 41
    22:47:53 ActiveCount: 0 poolSize: 7 queueSize: 0 taskCount: 41
    22:47:54 ActiveCount: 0 poolSize: 7 queueSize: 0 taskCount: 41
    22:47:55 ActiveCount: 0 poolSize: 7 queueSize: 0 taskCount: 41
    22:47:56 ActiveCount: 0 poolSize: 7 queueSize: 0 taskCount: 41
    22:47:57 ActiveCount: 0 poolSize: 5 queueSize: 0 taskCount: 41
    //由于keepAliveTime=10,大概10s后poolSize恢复为corePoolSize。
    22:47:58 ActiveCount: 0 poolSize: 3 queueSize: 0 taskCount: 41
    22:47:59 ActiveCount: 0 poolSize: 3 queueSize: 0 taskCount: 41
    22:48:00 ActiveCount: 0 poolSize: 3 queueSize: 0 taskCount: 41

    注意

    《阿里巴巴java开发手册》

    线程池不使用 Executors 去创建,而是通过 ThreadPoolExecutor 的方式,这样 的处理方式让写的同学更加明确线程池的运行规则,规避资源耗尽的风险。

    说明: Executors 返回的线程池对象的弊端如下:

    1. FixedThreadPool 和 SingleThreadPool : 允许的请求队列长度为 Integer.MAX_VALUE ,可能会堆积大量的请求,从而导致 OOM 。
    2. CachedThreadPool 和 ScheduledThreadPool : 允许的创建线程数量为 Integer.MAX_VALUE ,可能会创建大量的线程,从而导致 OOM 。

    Reference

  • 相关阅读:
    android点滴 之 进度条
    android点滴(26)之让线程拥有自己的消息循环
    Python property
    MD5加密
    哈希表加载xml文件
    .NET自定义控件制作
    如何用Treeview树加载xml
    xml的属性
    FFT实现——有趣的移位寄存流水线形式
    频率选择滤波器 线性时不变系统
  • 原文地址:https://www.cnblogs.com/sessionbest/p/9396706.html
Copyright © 2020-2023  润新知