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;
}

 1  public void execute(Runnable command) {
 2         if (command == null)
 3             throw new NullPointerException();
 4         /*
 5          * Proceed in 3 steps:
 6          *
 7          * 1. If fewer than corePoolSize threads are running, try to
 8          * start a new thread with the given command as its first
 9          * task.  The call to addWorker atomically checks runState and
10          * workerCount, and so prevents false alarms that would add
11          * threads when it shouldn‘t, by returning false.
12          *
13          * 2. If a task can be successfully queued, then we still need
14          * to double-check whether we should have added a thread
15          * (because existing ones died since last checking) or that
16          * the pool shut down since entry into this method. So we
17          * recheck state and if necessary roll back the enqueuing if
18          * stopped, or start a new thread if there are none.
19          *
20          * 3. If we cannot queue task, then we try to add a new
21          * thread.  If it fails, we know we are shut down or saturated
22          * and so reject the task.
23          */
24         int c = ctl.get();
25         if (workerCountOf(c) < corePoolSize) {
26             if (addWorker(command, true))
27                 return;
28             c = ctl.get();
29         }
30         if (isRunning(c) && workQueue.offer(command)) {
31             int recheck = ctl.get();
32             if (! isRunning(recheck) && remove(command))
33                 reject(command);
34             else if (workerCountOf(recheck) == 0)
35                 addWorker(null, false);
36         }
37         else if (!addWorker(command, false))
38             reject(command);
39     }

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

 1 /**
 2  * <pre>
 3  *
 4  * 代码和思路主要来自于：
 5  *
 6  * tomcat :
 7  *        org.apache.catalina.core.StandardThreadExecutor
 8  *
 9  * java.util.concurrent
10  * 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
11  *                              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）
12  *
13  * StandardThreadExecutor execute执行策略： 优先扩充线程到maxThread，再offer到queue，如果满了就reject
14  *                           比较适合于业务处理需要远程资源的场景
15  *
16  * </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。