Leader/Follower模式的简单实现

Leader/Follower相比较于普通的ThreadPool的优点

1、无需context switch，减少了线程间数据copy

2、无需维护一个队列，占用而外的内存空间

lf模式理解起来稍微有些困难，所以写了一个小的事例程序帮助自己理解

public class ThreadPool {
	private final static Object monitor = new Object();
	private final static int THREAD_POO_SIZE = 5;

	private Reactor handleSet = new Reactor();

	public ThreadPool(Reactor handleSet) {
		this.handleSet = handleSet;
	}

	public void init() {
		for (int i = 0; i < THREAD_POO_SIZE; i++) {
			new WorkThread(this).start();
		}
		this.promoteNewLeader();
	}

	public void join() {
		for (;;) {
			waitToLeader();
			// select, blocking
			Handle handle = handleSet.select();

			// promote new leader
			promoteNewLeader();

			// process handl
			handleSet.handle(handle);

			// reenter to next loop
		}
	}

	private void waitToLeader() {
		synchronized (monitor) {
			try {
				monitor.wait();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
	}

	public void promoteNewLeader() {
		synchronized (monitor) {
			monitor.notify();
		}
	}

	class WorkThread extends Thread {
		ThreadPool tp;

		public WorkThread(ThreadPool tp) {
			this.tp = tp;
		}

		@Override
		public void run() {
			tp.join();
		}

	}
}

在lf模式中，线程有3种状态

它们通过以下两个方法来实现切换：

waitToLeader

promoteNewLeader

利用了java线程间通信的特性， 实现leader/follower线程的切换

目前java实现线程间通信，有两种方法：

1、Object.wait, Object.notify

2、Condition.await, Condition.signal

另一个疑问，就是要在系统初始化好后，调用promoteNewLeader，提升一个线程作为leader thread，监听事件的到来。

lf thread pool改进点：

1、thread pool大小可调节，可以参考ThreadPoolExecutor的实现

2、更多通用化，抽取变化点

Leader/Follower 论文参考：

http://www.kircher-schwanninger.de/michael/publications/lf.pdf

http://www.cse.wustl.edu/~schmidt/PDF/reactor-siemens.pdf

http://www.cse.wustl.edu/~schmidt/PDF/proactor.pdf