ThreadPoolExecutor参数

1、ThreadPoolExecutor个参数的意义（类上的注释内容）

* @param corePoolSize the number of threads to keep in the
* pool, even if they are idle.
* @param maximumPoolSize the maximum number of threads to allow in the
* pool.
* @param keepAliveTime when the number of threads is greater than
* the core, this is the maximum time that excess idle threads
* will wait for new tasks before terminating.
* @param unit the time unit for the keepAliveTime
* argument.
* @param workQueue the queue to use for holding tasks before they
* are executed. This queue will hold only the <tt>Runnable</tt>
* tasks submitted by the <tt>execute</tt> method.
* @param threadFactory the factory to use when the executor
* creates a new thread.
* @param handler the handler to use when execution is blocked
* because the thread bounds and queue capacities are reached.

2、我对参数的理解(重要)

• corePoolSize：核心线程数，线程池创建时，就会创建的线程数。所有线程都执行完后，核心线程依然会保持。
• maximumPoolSize：最大的线程数。线程池最多会初始化maximumPoolSize个线程。
• keepAliveTime：idle线程存活时间。
• unit：keepAliveTime对应的时间单位。
• workQueue：队列，如果任务数已经达到corePoolSize，再向线程池中加入任务时，会将任务放到workQueue中。可以使用LinkedBlockingQueue，队列的数量没有限制。在构造BlockingQueue的时候，也可以传入最大值。如果有最大值，在queue中任务的数量达到最大值，再向线程池中加入任务时，就会启动新的线程，直到线程池中线程的数量达到maximumPoolSize为止。再向线程池中加入线程，会报错。
• threadFactory：新线程的构造器。
• handler：如果抛出异常，异常处理的Handler。

综上：线程池中的线程数量在线程池初始化的时候，为corePoolSize；随着加入线程池的任务数量增加， 运行的线程并不会增加，无法运行的任务会放到workQueue队列中；当workQueue队列已经放满了任务，新加入的任务会再启动新的线程来执行，直到正在运行的线程数量达到maximumPoolSize为止；再向线程池中添加任务，将会抛出异常。

3、验证各参数的代码

public static class ExecutorHelper {
        public static String getInfo(ThreadPoolExecutor executor) {
            StringBuilder sb = new StringBuilder();
            sb.append("************** corePoolSize: " + executor.getCorePoolSize());
            sb.append("************** poolSize: " + executor.getPoolSize());
            sb.append("************** activeCount: " + executor.getActiveCount());
            sb.append("************** completeTaskCount: " + executor.getCompletedTaskCount());
            sb.append("************** largestPoolSize: " + executor.getLargestPoolSize());
            sb.append("************** maximumPoolSize: " + executor.getMaximumPoolSize());
            sb.append("************** taskCount: " + executor.getTaskCount());
            sb.append("************** queueSize: " + executor.getQueue().size());
//            sb.append("************** corePoolSize: " + executor.getCorePoolSize());
//            sb.append("************** corePoolSize: " + executor.getCorePoolSize());

            return sb.toString();
        }
    }

    public static class MyRunnable implements Runnable {

        private ThreadPoolExecutor executor;
        public MyRunnable(ThreadPoolExecutor executor) {
            this.executor = executor;

            System.out.println(ExecutorHelper.getInfo(executor));
        }

        @Override
        public void run() {

            Thread th = Thread.currentThread();
            System.out.println(th.getName());
//            System.out.println(ExecutorHelper.getInfo(executor));

            try {
                Thread.sleep(1000 * 30);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    public static void main(String[] args) throws Exception {
        ThreadPoolExecutor executor = new ThreadPoolExecutor(2,
                5, 0L, TimeUnit.MILLISECONDS,
                new LinkedBlockingQueue<Runnable>(4), Executors.defaultThreadFactory(),
                new ThreadPoolExecutor.AbortPolicy());

        for (int i = 0; i < 10; i++) {
            Runnable runnable = new MyRunnable(executor);
            executor.submit(runnable);
            Thread.sleep(1000);
        }
    }

4、输出的内容：

************** corePoolSize: 2************** poolSize: 0************** activeCount: 0************** completeTaskCount: 0************** largestPoolSize: 0************** maximumPoolSize: 5************** taskCount: 0************** queueSize: 0
pool-2-thread-1
************** corePoolSize: 2************** poolSize: 1************** activeCount: 1************** completeTaskCount: 0************** largestPoolSize: 1************** maximumPoolSize: 5************** taskCount: 1************** queueSize: 0
pool-2-thread-2
************** corePoolSize: 2************** poolSize: 2************** activeCount: 2************** completeTaskCount: 0************** largestPoolSize: 2************** maximumPoolSize: 5************** taskCount: 2************** queueSize: 0
************** corePoolSize: 2************** poolSize: 2************** activeCount: 2************** completeTaskCount: 0************** largestPoolSize: 2************** maximumPoolSize: 5************** taskCount: 3************** queueSize: 1
************** corePoolSize: 2************** poolSize: 2************** activeCount: 2************** completeTaskCount: 0************** largestPoolSize: 2************** maximumPoolSize: 5************** taskCount: 4************** queueSize: 2
************** corePoolSize: 2************** poolSize: 2************** activeCount: 2************** completeTaskCount: 0************** largestPoolSize: 2************** maximumPoolSize: 5************** taskCount: 5************** queueSize: 3
************** corePoolSize: 2************** poolSize: 2************** activeCount: 2************** completeTaskCount: 0************** largestPoolSize: 2************** maximumPoolSize: 5************** taskCount: 6************** queueSize: 4
pool-2-thread-3
************** corePoolSize: 2************** poolSize: 3************** activeCount: 3************** completeTaskCount: 0************** largestPoolSize: 3************** maximumPoolSize: 5************** taskCount: 7************** queueSize: 4
pool-2-thread-4
************** corePoolSize: 2************** poolSize: 4************** activeCount: 4************** completeTaskCount: 0************** largestPoolSize: 4************** maximumPoolSize: 5************** taskCount: 8************** queueSize: 4
pool-2-thread-5
Exception in thread "main" java.util.concurrent.RejectedExecutionException
    at java.util.concurrent.ThreadPoolExecutor$AbortPolicy.rejectedExecution(ThreadPoolExecutor.java:1768)
************** corePoolSize: 2************** poolSize: 5************** activeCount: 5************** completeTaskCount: 0************** largestPoolSize: 5************** maximumPoolSize: 5************** taskCount: 9************** queueSize: 4
    at java.util.concurrent.ThreadPoolExecutor.reject(ThreadPoolExecutor.java:767)
    at java.util.concurrent.ThreadPoolExecutor.execute(ThreadPoolExecutor.java:658)
    at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:78)
    at com.jd.wms.inbound.service.socket.client.DhSocketClient.main(DhSocketClient.java:122)
pool-2-thread-1
pool-2-thread-2
pool-2-thread-3
pool-2-thread-4