loopingthread.java

来自「mysql集群」· Java 代码 · 共 114 行

/*
 * 	This program is free software; you can redistribute it and/or modify it under the terms of 
 * the GNU General Public License as published by the Free Software Foundation; either version 3 of the License, 
 * or (at your option) any later version. 
 * 
 * 	This program is distributed in the hope that it will be useful, 
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  
 * See the GNU General Public License for more details. 
 * 	You should have received a copy of the GNU General Public License along with this program; 
 * if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */
package com.meidusa.amoeba.util;

import org.apache.log4j.Logger;

/**
 * 
 * 该类作为线程提供了循环的基本功能，能够处理一个简单的循环。 最大特点是每一次通过循环，事件处理线程可以轻易地安排处理类似事件队列。
 * 
 */
public class LoopingThread extends Thread {
	private static Logger log = Logger.getLogger(LoopingThread.class);
	public LoopingThread() {
	}

	/**
	 * 指定一个特殊的命名
	 * 
	 * @param name
	 */
	public LoopingThread(String name) {
		super(name);
	}

	/**
	 * 允许关闭该线程，如果此次请求并发本线程发出，则需要清理相关的事情。
	 * 
	 */
	public synchronized void shutdown() {
		_running = false;

		// only kick the thread if it's not requesting it's own shutdown
		if (this != Thread.currentThread()) {
			kick();
		}
	}

	/**
	 * 循环
	 */
	public void run() {
		if(log.isDebugEnabled()){
			log.debug(this.getName() +" LoopingThread willStart....");
		}
		try {
			willStart();

			while (isRunning()) {
				try {
					iterate();
				} catch (Exception e) {
					handleIterateFailure(e);
				}
			}

		} finally {
			didShutdown();
		}
	}

	/**
	 * 
	 * 检查线程是否处于运行状态。如果该方法返回false，此时线程如果处于iterate调用，将会退出循环。 这个方法作为循环线程的一部分
	 * {@link #run}
	 * 
	 */
	public synchronized boolean isRunning() {
		return _running;
	}

	/**
	 * 当线程在退出的时候，需要清理内部环境或者进行其他操作
	 */
	protected void kick() {
		// nothing doing by default
	}

	/**
	 * 线程在开始执行的时候，可以在这个方法里面做一些初始化的动作
	 */
	protected void willStart() {
	}

	protected void iterate() {
		throw new RuntimeException("Derived class must implement iterate().");
	}

	protected void handleIterateFailure(Exception e) {
		// log the exception

		// and shut the thread down
		log.error("error:",e);
		shutdown();
	}

	/**
	 * 完成shutdown动作以后。即将退出整个线程的运行。
	 */
	protected void didShutdown() {
	}

	protected boolean _running = true;
}