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。