Executors way to create native thread pool
Java thread pool inside the top-level interface is Executor , but is not a strict sense Executor thread pools, but only one thread of execution tool. The interface is a real thread pool ExecutorService
Thread pool does not recommend the use of Executors to create, but by ThreadPoolExecutor way, this approach allows the students to write more explicit operating rules thread pool, to avoid the risk of resource depletion. Description: Executors disadvantages of each method:
. 1) and newFixedThreadPool newSingleThreadExecutor:
主要问题是堆积的请求处理队列可能会耗费非常大的内存，甚至OOM。
2) and newCachedThreadPool newScheduledThreadPool:
主要问题是线程数最大数是Integer.MAX_VALUE，可能会创建数量非常多的线程，甚至OOM。
2、无界队列。使用无界队列（典型的便是采用预定义容量的 LinkedBlockingQueue，理论上是该缓冲队列可以对无限多的任务排队）将导致在所有 corePoolSize 线程都工作的情况下将新任务加入到缓冲队列中。这样，创建的线程就不会超过 corePoolSize，也因此，maximumPoolSize 的值也就无效了。当每个任务完全独立于其他任务，即任务执行互不影响时，适合于使用无界队列。newFixedThreadPool采用的便是这种策略。
3、有界队列。当使用有限的 maximumPoolSizes 时，有界队列（一般缓冲队列使用ArrayBlockingQueue，并制定队列的最大长度）有助于防止资源耗尽，但是可能较难调整和控制，队列大小和最大池大小需要相互折衷，需要设定合理的参数。
ThreadPoolExecutor threadPool = new ThreadPoolExecutor(2, 4, 3,
TimeUnit. SECONDS, new ArrayBlockingQueue<Runnable>(3),
new ThreadPoolExecutor.DiscardOldestPolicy());Bounded queue: if the queue length exceeds the length of a walking strategy rejected, otherwise access queue for processing
