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

• 深入浅出Java线程池