线程池ThreadPoolExecutor之阻塞队列

在近期的性能优化中，使用了线程池，线程池的定义如下：

ExecutorService executorService = new ThreadPoolExecutor(threadPoolSize, 
                threadPoolMaxSize, timeout,
                TimeUnit.SECONDS,
                new LinkedBlockingQueue<>(30000),
                Executors.defaultThreadFactory(),
                new ThreadPoolExecutor.AbortPolicy());

现有55000个请求，大概在发送30000零几个请求的后，就不在发送请求了。countdownLuch也不做减法了。

原因是ThreadPoolExecutor 中的 new LinkedBlockingQueue<>(30000)，即阻塞队列为30000个，在往线程池中塞请求的时候，塞的请求多余3W个时候，因为我使用的是ThreadPoolExceutor默认的拒绝策略。所有其他的1W多个都抛弃了。

为什么不是整整3W，而是3W零几个呢，因为最初发送的几个请求返回了结果，释放了几个线程，在3W个队列塞满之前，又多加了几个进去。

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问题的定位

最初的猜猜是 1。出现了死锁 ，使用jps -m 查看死锁（参考这篇文章），也可以使用jstack PID 查看（参考这篇文章）

2。因为请求时间过长，线程池资源被耗尽

使用jstack PID后，发现下面的警告

at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x0000000080135840> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

  Locked ownable synchronizers:
  --
  "pool-1-thread-6" #114 prio=5 os_prio=0 tid=0x00007f54908f5000 nid=0x5f67    waiting on condition [0x00007f5441901000]
java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x0000000080135840> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

    Locked ownable synchronizers:
  --
  "pool-1-thread-5" #113 prio=5 os_prio=0 tid=0x00007f54908f3000 nid=0x5f66     waiting on condition [0x00007f5441a02000]
 java.lang.Thread.State: WAITING (parking)
    at sun.misc.Unsafe.park(Native Method)
    - parking to wait for  <0x0000000080135840> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
    at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
    at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:2039)
    at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:442)
    at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:1074)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1134)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)

看到疑问的时候，想线程池为什么会等待呢，阻塞队列为什么会等待呢

突然想到了上面的问题。

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解决方案：

1. 可以直接修改阻塞队列的大小

2. 将5W的请求分配，例如每100个一批发送请求，等这100个请求的结果都拿到后，在发送第二批的请求。这样也可以方式突然发送5W的请求，内存等资源被耗尽等问题