Java，线程池，ThreadPoolExecutor

  ThreadPoolExecutor定义

public ThreadPoolExecutor(int corePoolSize,
                          int maximumPoolSize,
                          long keepAliveTime,
                          TimeUnit unit,
                          BlockingQueue<Runnable> workQueue,
                          ThreadFactory threadFactory)

Creates a new ThreadPoolExecutorwith the given initial parameters and default rejected execution handler.

Parameters:

corePoolSize - the number of threads to keep in the pool, even if they are idle.

maximumPoolSize - the maximum number of threads to allow in the pool.

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.

unit - the time unit for the keepAliveTime argument.

workQueue - the queue to use for holding tasks before they are executed. This queue will hold only the Runnable tasks submitted by the execute method.

threadFactory - the factory to use when the executor creates a new thread.

Throws:

IllegalArgumentException - if corePoolSize or keepAliveTime less than zero, or if maximumPoolSize less than or equal to zero, or if corePoolSize greater than maximumPoolSize.

NullPointerException - if workQueue or threadFactory are null.

 

  ThreadPoolExecutor举例

ThreadPoolExecutor threadPool = new ThreadPoolExecutor(2, 4, 3, TimeUnit.SECONDS,
                new ArrayBlockingQueue<Runnable>(3),
                new ThreadPoolExecutor.DiscardOldestPolicy()
        );

 

  如何给线程池添加任务

第一步：定义任务

public class MyTask implements Runnable{

    private String name = null;
    public MyTask(final String name){
        this.name = name;
    }
    @Override
    public void run() {
        // TODO Auto-generated method stub
        System.out.println("My task is " + this.name);
    }

}

 

第二步：添加任务

threadPool.execute(new MyTask("killing evils~"));

 

  线程池中的线程，是如何动态调整的

(1) 正常情况下，最多去维护corePoolSize 个线程来执行任务；

(2) 如果任务不断增多，corePoolSize做不过来了，可以向workQueue里塞

(3) 如果队列塞满了，那么再尝试启新线程来做，最多会再启(maximumPoolSize-corePoolSize)个

(4) 如果任务还在不断增多，workQueue也满了，所有maximumPoolSize都执行不过来了，那么开始执行放弃策略。

 

这里有比较有意思的讲解：

http://wenku.baidu.com/view/8f4fc14ffe4733687e21aa55.html