• 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
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  • 原文地址：https://www.cnblogs.com/sessionbest/p/9396706.html
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