Tomcat中的线程池StandardThreadExecutor

之所以今天讨论它，因为在motan的的NettyServer中利用它这个线程池可以作为业务线程池，它定制了一个自己的线程池。当然还是基于jdk中的ThreadExecutor中的构造方法和execute方法，然后在外边包装一层。

public ThreadPoolExecutor(int corePoolSize,

                          int maximumPoolSize,
                          long keepAliveTime,
                          TimeUnit unit,
                          BlockingQueue<Runnable> workQueue,
                          ThreadFactory threadFactory,
                          RejectedExecutionHandler handler) {
    if (corePoolSize < 0 ||
        maximumPoolSize <= 0 ||
        maximumPoolSize < corePoolSize ||
        keepAliveTime < 0)
        throw new IllegalArgumentException();
    if (workQueue == null || threadFactory == null || handler == null)
        throw new NullPointerException();
    this.corePoolSize = corePoolSize;
    this.maximumPoolSize = maximumPoolSize;
    this.workQueue = workQueue;
    this.keepAliveTime = unit.toNanos(keepAliveTime);
    this.threadFactory = threadFactory;
    this.handler = handler;
}

  public void execute(Runnable command) {
         if (command == null)
             throw new NullPointerException();
         /*
          * Proceed in 3 steps:
          *
          * 1. If fewer than corePoolSize threads are running, try to
          * start a new thread with the given command as its first
          * task.  The call to addWorker atomically checks runState and
          * workerCount, and so prevents false alarms that would add
          * threads when it shouldn't, by returning false.
          *
          * 2. If a task can be successfully queued, then we still need
          * to double-check whether we should have added a thread
          * (because existing ones died since last checking) or that
          * the pool shut down since entry into this method. So we
          * recheck state and if necessary roll back the enqueuing if
          * stopped, or start a new thread if there are none.
          *
          * 3. If we cannot queue task, then we try to add a new
          * thread.  If it fails, we know we are shut down or saturated
          * and so reject the task.
          */
         int c = ctl.get();
         if (workerCountOf(c) < corePoolSize) {
             if (addWorker(command, true))
                 return;
             c = ctl.get();
         }
         if (isRunning(c) && workQueue.offer(command)) {
             int recheck = ctl.get();
             if (! isRunning(recheck) && remove(command))
                 reject(command);
             else if (workerCountOf(recheck) == 0)
                 addWorker(null, false);
         }
         else if (!addWorker(command, false))
             reject(command);
     }

ThreadExecutor中的execute方法

从execute  方法的注释清晰得知，传统线程加入线程池执行过程分3步

小于等于Coresize： 创建线程之行

大于CoreSize  加入队列

队列满且小于maxSize  有空闲线程使用空闲线程执行，没有的话，创建线程执行

大于maxSize  拒绝策略执行

---

现在需要按照如下方式改造

 /**
  * <pre>
  *
  * 代码和思路主要来自于：
  *
  * tomcat :
  *        org.apache.catalina.core.StandardThreadExecutor
  *
  * java.util.concurrent
  * threadPoolExecutor execute执行策略：        优先offer到queue，queue满后再扩充线程到maxThread，如果已经到了maxThread就reject
  *                              比较适合于CPU密集型应用（比如runnable内部执行的操作都在JVM内部，memory copy, or compute等等）
  *
  * StandardThreadExecutor execute执行策略： 优先扩充线程到maxThread，再offer到queue，如果满了就reject
  *                           比较适合于业务处理需要远程资源的场景
  *
  * </pre>

具体的方式自己改造一个队列，在队列入队的方式下功夫。