集羣環境中利用Memcached CAS原子操作計數

利用Memcached CAS原子操作，確保集羣/多線程環境彙總累加操作是有效的，而不會覆蓋其他線程的累加結果。

package org.pile.memcached;

import java.io.IOException;
import java.util.Random;
import java.util.concurrent.atomic.AtomicInteger;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.pile.util.LogWriter;

import net.spy.memcached.CASValue;

public class CASLockServlet extends HttpServlet {
	//private static final int[] LEVEL = {10,50,200,500,1000,5000,10000,20000};
	private static final String CACHE_KEY = "CASLOCK";
	private volatile static AtomicInteger visitTimes = new AtomicInteger();
	//private Random		  random     = new Random();

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String responseBody = null;
		if(null != request.getParameter("reset")){
			visitTimes = new AtomicInteger();
			MemCache.setCache(CACHE_KEY, 0, 0);
			LogWriter.printLog("Reset servlet status.");
			ResponseBuilder.buildResponse("Reset ok!", response);
			return;
		}
		if(null != request.getParameter("print")){
			responseBody = "Servlet Object value ::" + visitTimes.intValue();
			responseBody += " Memcached Object value ::" + MemCache.getCache(CACHE_KEY).toString();
			LogWriter.printLog("Print servlet status.");
			ResponseBuilder.buildResponse(responseBody, response);
			return;
		}
		int step  = 1;
		visitTimes.addAndGet(step);
		LogWriter.printLog("Update local value::" + visitTimes.intValue());
		while(true){
			LogWriter.printLog("Begin to get CASValue::" + visitTimes.intValue());
			CASValue<Object> casValue = MemCache.getCasId(CACHE_KEY);
			LogWriter.printLog("End to get CASValue::" + casValue.getValue().toString());
			int cachTimes = Integer.parseInt(casValue.getValue().toString()) + step;
			if(MemCache.casCache(CACHE_KEY, casValue.getCas(), String.valueOf(cachTimes))){
				LogWriter.printLog("Success to CAS Cache::" + cachTimes);
				break;
			}
			else{
				LogWriter.printLog("Fail to CAS Cache::" + cachTimes);
				try{
					Thread.sleep(200);
				}
				catch(Exception exp){
					exp.printStackTrace();
				}
			}
		}
	}
}