本文介绍了一种针对 Memcached Java 客户端的优化方案，通过封装客户端来解决并发写入相同 key 的问题，并提供了一个示例实现。
memcached java客户端 https://github.com/gwhalin/Memcached-Java-Client 在使用中发现对 同一JVM种对相同key的写操作时并发写的，这一点很不好，下面是对 memcached客户端优化使用,参考oscache的机制。
对MemCachedClient 二次封装目的：
优化对同一key的读写操作
对客户端的二次封装：
import java.util.Date;
import java.util.concurrent.ConcurrentHashMap;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import com.danga.MemCached.MemCachedClient;
/**
* memcached客户端优化，确保对相同key的写操作并发执行时只要一次写入memcached
* @author mengxiansheng
*
*/
public class CacheTuning {
// 创建全局的唯一实例
private static ConcurrentHashMap updateStates = new ConcurrentHashMap();
protected static MemCachedClient memCachedClient = null;
private static transient final Log log = LogFactory
.getLog(CacheTuning.class);
public void setMemCachedClient(MemCachedClient mcc) {
this.memCachedClient = mcc;
}
protected EntryUpdateState getUpdateState(String key) {
EntryUpdateState updateState;
// Try to find the matching state object in the updating entry map.
updateState = (EntryUpdateState) updateStates.get(key);
if (updateState == null) {
// It's not there so add it.
updateState = new EntryUpdateState();
updateStates.put(key, updateState);
} else {
// Otherwise indicate that we start using it to prevent its
// removal
// until all threads are done with it.
updateState.incrementUsageCounter();
}
return updateState;
}
/**
* 释放key对EntryUpdateState实例的使用，当没有线程使用EntryUpdateState实例是，将该实例在map中删除
*
* @param state
* the state to release the usage of
* @param key
* the associated key.
*/
protected void releaseUpdateState(EntryUpdateState state, String key) {
int usageCounter = state.decrementUsageCounter();
checkEntryStateUpdateUsage(key, state, usageCounter);
}
/**
* Utility method to check if the specified usage count is zero, and if so
* remove the corresponding EntryUpdateState from the updateStates. This is
* designed to factor common code.
*
* Warning: This method should always be called while holding both the
* updateStates field and the state parameter
*
* @throws Exception
*/
private void checkEntryStateUpdateUsage(String key, EntryUpdateState state,
int usageCounter) {
// Clean up the updateStates map to avoid a memory leak once no thread
// is using this EntryUpdateState instance anymore.
if (usageCounter == 0) {
log.debug("在更新状态列表中删除：" + key + "\t");
EntryUpdateState removedState = (EntryUpdateState) updateStates
.remove(key);
if (state != removedState) {
if (log.isErrorEnabled()) {
try {
throw new Exception(
"memcached: internal error: removed state ["
+ removedState + "] from key [" + key
+ "] whereas we expected [" + state
+ "]");
} catch (Exception e) {
log.error(e);
}
}
}
}
}
/**
* 保护型构造方法，不允许实例化！
*
*/
protected CacheTuning() {
}
/**
* 添加一个指定的值到缓存中.
*
* @param key
* @param value
* @return
*/
public boolean putInCache(String key, Object value, long secords) {
// set方法：在cache中存储一个指定对象
// add 和replace 方法功能差不多
// add -- 如果不存在 这个key的对象，将会存储一个对象到cache中
// replace --只有当存在指定key对象的时候 会覆盖已有对象
EntryUpdateState updateState = getUpdateState(key);
try {
boolean ok = memCachedClient.add(key, value, new Date(
secords * 1000));
completeUpdate(key);
log.debug(key + "添加成功，值：" + value.toString());
return ok;
} catch (Exception e) {
e.printStackTrace();
this.cancelUpdate(key);
} finally {
// Make sure we release the usage count for this
// EntryUpdateState since we don't use it anymore. If the
// current thread started the update, then the counter was
// increased by one in startUpdate()
log.debug(Thread.currentThread().getId() + " 唤醒:" + key);
}
return false;
}
/**
* Removes the update state for the specified key and notifies any other
* threads that are waiting on this object. This is called automatically by
* the {@link #putInCache} method, so it is possible that no
* EntryUpdateState was hold when this method is called.
*
* @param key
* The cache key that is no longer being updated.
*/
protected void completeUpdate(String key) {
EntryUpdateState state;
state = (EntryUpdateState) updateStates.get(key);
if (state != null) {
synchronized (state) {
int usageCounter = state.completeUpdate();
state.notify();
checkEntryStateUpdateUsage(key, state, usageCounter);
}
} else {
// If putInCache() was called directly (i.e. not as a result of a
// NeedRefreshException) then no EntryUpdateState would be found.
}
}
public boolean replace(String key, Object value) {
return memCachedClient.replace(key, value);
}
/**
* 在缓存中删除指定的key
*
* @param key 指定删除的key
*
* @return <code>true</code>, 如果删除成功
*/
public boolean delete(String key) {
return memCachedClient.delete(key);
}
/**
* 根据指定的关键字获取对象.
*
* @param key
* @return
*/
public Object getFromCache(String key) throws NeedsRefreshException {
EntryUpdateState updateState = null;
updateState = getUpdateState(key);
Object obj = memCachedClient.get(key);
//log.debug("key:"+key+" 的缓存对象 is null ? "+(obj==null));
if(obj!=null){
return obj;
}
boolean reload = false;
if (obj == null) {// 不存在缓存数据，数据已过期或者第一次访问
try {
synchronized (updateState) {
if (updateState.isAwaitingUpdate()
|| updateState.isCancelled()) {// 第一次访问该数据或者前面线程对该数据的更新已取消
updateState.startUpdate();// 开始更新
} else if (updateState.isUpdating()) {// 该数据正在更新
// //其他线程正在更新这个缓存
do {
try {
updateState.wait();
} catch (InterruptedException e) {
}
} while (updateState.isUpdating());
if (updateState.isCancelled()) {// 更新被取消
updateState.startUpdate();
} else if (updateState.isComplete()) {// 其他线程完成了对该数据的更新
reload = true;
} else {
log.error("Invalid update state for cache entry "
+ key);
}
} else {// 其他线程已经对该数据更新完成，重新获取数据
reload = true;
}
}
} catch (Exception e) {
log.error(e.getMessage(), e.getCause());
} finally {
// Make sure we release the usage count for this
// EntryUpdateState since we don't use it anymore. If
// the current thread started the update, then the
// counter was
// increased by one in startUpdate()
releaseUpdateState(updateState, key);// 释放 对 EntryUpdateState
// 的使用
// EntryUpdateState的计数器减一
}
}
if (reload) {
obj = memCachedClient.get(key);
}
if (obj == null) {// 没有获取到缓存对象，则更新
throw new NeedsRefreshException("需要重新获取:" + key);
}
return obj;
}
private void cancelUpdate(String key) {
// TODO Auto-generated method stub
EntryUpdateState state;
if (key != null) {
state = (EntryUpdateState) updateStates.get(key);
if (state != null) {
synchronized (state) {
int usageCounter = state.cancelUpdate();
state.notify();
checkEntryStateUpdateUsage(key, state, usageCounter);
}
} else {
if (log.isErrorEnabled()) {
log
.error("internal error: expected to get a state from key ["
+ key + "]");
}
}
}
}
public boolean putInCache(String key, Object value) {
// TODO Auto-generated method stub
return this.putInCache(key, value, 0);
}
}
缓存实体状态类：
/**
* 缓存更新状态。
* Holds the state of a Cache Entry that is in the process of being (re)generated.
* This is not synchronized; the synchronization must be handled by the calling
* classes.
*
* @author Author: mengxiansheng
*/
public class EntryUpdateState {
/**
* 初始化状态
*/
public static final int NOT_YET_UPDATING = -1;
/**
* 正在处理中状态
*/
public static final int UPDATE_IN_PROGRESS = 0;
/**
* 更新完成状态
*/
public static final int UPDATE_COMPLETE = 1;
/**
* 取消更新状态
*/
public static final int UPDATE_CANCELLED = 2;
/**
*初始化状态
*/
int state = NOT_YET_UPDATING;
/**
* 线程计数器，实例可以控制这个计数器，当计数器是0的时候，可以说明缓存实例已经被释放
* 计数器受 EntryStateUpdate实例监听器的保护
* A counter of the number of threads that are coordinated through this instance. When this counter gets to zero, then the reference to this
* instance may be released from the Cache instance.
* This is counter is protected by the EntryStateUpdate instance monitor.
*/
private int nbConcurrentUses = 1;
/**
* 是否等待更新
* 如果是初始化状态，则等待更新
* This is the initial state when an instance this object is first created.
* It indicates that a cache entry needs updating, but no thread has claimed
* responsibility for updating it yet.
*/
public boolean isAwaitingUpdate() {
return state == NOT_YET_UPDATING;
}
/**
* 更新已经被取消
* The thread that was responsible for updating the cache entry (ie, the thread
* that managed to grab the update lock) has decided to give up responsibility
* for performing the update. OSCache will notify any other threads that are
* waiting on the update so one of them can take over the responsibility.
*/
public boolean isCancelled() {
return state == UPDATE_CANCELLED;
}
/**
* 更新完成
* The update of the cache entry has been completed.
*/
public boolean isComplete() {
return state == UPDATE_COMPLETE;
}
/**
* 正在更新
* The cache entry is currently being generated by the thread that got hold of
* the update lock.
*/
public boolean isUpdating() {
return state == UPDATE_IN_PROGRESS;
}
/**
* 取消更新,只能是出于增在更新状态UPDATE_IN_PROGRESS 的可以取消更新
* Updates the state to <code>UPDATE_CANCELLED</code>. This should <em>only<em>
* be called by the thread that managed to get the update lock.
* @return the counter value after the operation completed
*/
public int cancelUpdate() {
// if (state != UPDATE_IN_PROGRESS) {
// throw new IllegalStateException("Cannot cancel cache update - current state (" + state + ") is not UPDATE_IN_PROGRESS");
// }
state = UPDATE_CANCELLED;
return decrementUsageCounter();
}
/**
* 完成更新
* Updates the state to <code>UPDATE_COMPLETE</code>. This should <em>only</em>
* be called by the thread that managed to get the update lock.
* @return the counter value after the operation completed
*/
public int completeUpdate() {
if (state != UPDATE_IN_PROGRESS) {
throw new IllegalStateException("Cannot complete cache update - current state (" + state + ") is not UPDATE_IN_PROGRESS");
}
state = UPDATE_COMPLETE;
return decrementUsageCounter();
}
/**
* 开始更新，当状态不是初始状态并且不是取消状态，才可以调用此方法，否则报异常
* Attempt to change the state to <code>UPDATE_IN_PROGRESS</code>. Calls
* to this method must be synchronized on the EntryUpdateState instance.
* @return the counter value after the operation completed
*/
public int startUpdate() {
if ((state != NOT_YET_UPDATING) && (state != UPDATE_CANCELLED)) {
throw new IllegalStateException("Cannot begin cache update - current state (" + state + ") is not NOT_YET_UPDATING or UPDATE_CANCELLED");
}
state = UPDATE_IN_PROGRESS;
return incrementUsageCounter();
}
/**
* 并发数增加
* Increments the usage counter by one
* @return the counter value after the increment
*/
public synchronized int incrementUsageCounter() {
nbConcurrentUses++;
return nbConcurrentUses;
}
/**
* 获取并发数
* Gets the current usage counter value
* @return a positive number.
*/
public synchronized int getUsageCounter() {
return nbConcurrentUses;
}
/**
* 计数器递减,并发数<=0时抛出异常.
* Decrements the usage counter by one. This method may only be called when the usage number is greater than zero
* @return the counter value after the decrement
*/
public synchronized int decrementUsageCounter() {
if (nbConcurrentUses <=0) {
throw new IllegalStateException("Cannot decrement usage counter, it is already equals to [" + nbConcurrentUses + "]");
}
nbConcurrentUses--;
return nbConcurrentUses;
}
}
需要刷新异常：
/**
*
*当缓存实体过期或不存在时抛出异常
* @author mengxiansheng
*/
public final class NeedsRefreshException extends Exception {
/**
*
*/
private static final long serialVersionUID = 1L;
/**
* Current object in the cache
*/
private Object cacheContent = null;
/**
* Create a NeedsRefreshException
*/
public NeedsRefreshException(String message, Object cacheContent) {
super(message);
this.cacheContent = cacheContent;
}
/**
* Create a NeedsRefreshException
*/
public NeedsRefreshException(Object cacheContent) {
super();
this.cacheContent = cacheContent;
}
/**
* Retrieve current object in the cache
*/
public Object getCacheContent() {
return cacheContent;
}
}
spring 管理配置
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd"> <bean class="ApplicationContextUtil"></bean> <!--socket连接池--> <bean id="SockIOPool" class="com.danga.MemCached.SockIOPool" factory-method="getInstance" init-method="initialize"> <!--服务器列表，可以根据需要增减--> <property name="servers"> <list> <value>127.0.0.1:11211</value> </list> </property> <!--服务器权重，根据内存大小分配--> <property name="weights"> <list> <value>2</value> </list> </property> <!--初始化，最小，最大连接数，建议开发环境使用1，1，5，线上环境使用5，5，250--> <property name="initConn" value="1"></property> <property name="minConn" value="1"></property> <property name="maxConn" value="5"></property> <!--时间--> <property name="maxIdle" value="21600000"></property> <property name="maintSleep" value="30000"></property> <property name="nagle" value="false"></property> <property name="socketTO" value="3000"></property> <property name="socketConnectTO" value="3000"></property> </bean> <bean name="MemCachedClient" class="com.danga.MemCached.MemCachedClient" depends-on="SockIOPool"> <property name="compressEnable" value="true"></property> <property name="compressThreshold" value="131072"></property> </bean> <bean name="Mem" class="CacheTuning"> <property name="memCachedClient" ref="MemCachedClient" /> </bean> </beans>
并发测试：
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
public class Test {
//ApplicationContextUtil 类自己实现，用来加载spring配置文件，
static CacheTuning mt=(CacheTuning)ApplicationContextUtil.getContext().getBean("Mem");
private static transient final Log log = LogFactory
.getLog(Test.class);
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
long t1=System.currentTimeMillis();
for(int i=0;i<1000;i++){
Thread tt=new Thread(new ts().setTime(t1));
tt.start();
}
}
}
class ts implements java.lang.Runnable{
private static transient final Log log = LogFactory
.getLog(ts.class);
long t1=0;
public ts setTime(long t1){
this.t1=t1;
return this;
}
public void run() {
// TODO Auto-generated method stub
String aa=null;
long _t1=System.currentTimeMillis();
try{
Test.mt.delete("keyss");
aa=(String)Test.mt.getFromCache("keyss");
}catch(NeedsRefreshException e){
aa="kdj快来撒飞机快lsd就疯了";
Test.mt.putInCache("keyss", aa,100);
log.info(Thread.currentThread().getId()+"新增：keyss");
}
long t2=System.currentTimeMillis();
log.info(Thread.currentThread().getId()+"耗时：\t"+(t2-_t1)+"\t总耗时\t"+(t2-t1)+"\t"+aa);
}
}
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