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：

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 。
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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ThreadPoolExecutor执行过程分析

ThreadPoolExecutor

ThreadPoolExecutor 测试代码

执行结果

注意

Reference

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