代码中实际运用memcached——java
以下文章取自：http://jameswxx.iteye.com/blog/1168711
memcached的java客户端有好几种，http://code.google.com/p/memcached/wiki/Clients 罗列了以下几种
Html代码
[*]spymemcached
[*]
[*] * http://www.couchbase.org/code/couchbase/java
[*] o An improved Java API maintained by Matt Ingenthron and others at Couchbase.
[*] o Aggressively optimised, ability to run async, supports binary protocol, support Membase and Couchbase features, etc. See site for details.
[*]
[*]Java memcached client
[*]
[*] * http://www.whalin.com/memcached
[*] o A Java API is maintained by Greg Whalin from Meetup.com.
[*]
[*]More Java memcached clients
[*]
[*] * http://code.google.com/p/javamemcachedclient
[*] * http://code.google.com/p/memcache-client-forjava
[*] * http://code.google.com/p/xmemcached
[*]
[*]Integrations
[*]
[*] * http://code.google.com/p/simple-spring-memcached
[*] * http://code.google.com/p/memcached-session-manager
我看的是第二个：Java memcached client源码，代码很简洁，一共只有9个类，最主要的有以下三个
MemcachedClient.java 客户端，负责提供外出程序接口，如get/set方法等等
SockIOPool.java 一个自平衡的连接池
NativeHandler.java 负责部分数据类型的序列化
它包含以下几个部分
1：key的服务端分布
2：数据序列化和压缩
3：连接池(连接方式和池的动态自动平衡)
4：failover和failback机制
5：和memcached服务器的通讯协议
关于这几个点，我从key的set/get说起，会贯穿上面列举的4个部分。这个文章写下来，本来是作为一个笔记，思维比较跳跃，可能不是很连贯，如有疑问，欢迎站内交流。这个client的代码
很简洁明了，我也没有加过多注释，只是理了一个脉络。
从客户端自带的测试代码开始
Java代码
[*]package com.meetup.memcached.test;
[*]import com.meetup.memcached.*;
[*]import org.apache.log4j.*;
[*]
[*]public class TestMemcached{
[*] public static void main(String[] args) {
[*] BasicConfigurator.configure();
[*] String[] servers = { "127.0.0.1:12000"};
[*] SockIOPool pool = SockIOPool.getInstance();
[*] pool.setServers( servers );
[*] pool.setFailover( true );//故障转移
[*] pool.setInitConn( 10 ); //初始化连接为10
[*] pool.setMinConn( 5 );//最小连接为5
[*] pool.setMaxConn( 250 );//最大连接为250
[*] pool.setMaintSleep( 30 );//平衡线程休眠时间为30ms
[*] pool.setNagle( false );//Nagle标志为false
[*] pool.setSocketTO( 3000 );//响应超时时间为3000ms
[*] pool.setAliveCheck( true );//需要可用状态检查
[*] //初始化连接池，默认名称为"default"
[*] pool.initialize();
[*] //新建一个memcached客户端，如果没有给名字
[*] MemcachedClient mcc = new MemcachedClient();
[*]
[*] // turn off most memcached client logging:
[*] com.meetup.memcached.Logger.getLogger( MemcachedClient.class.getName() ).setLevel( com.meetup.memcached.Logger.LEVEL_WARN );
[*]
[*] for ( int i = 0; i < 10; i++ ) {
[*] boolean success = mcc.set( "" + i, "Hello!" );
[*] String result = (String)mcc.get( "" + i );
[*] System.out.println( String.format( "set( %d ): %s", i, success ) );
[*] System.out.println( String.format( "get( %d ): %s", i, result ) );
[*] }
[*]
[*] System.out.println( "\n\t -- sleeping --\n" );
[*] try { Thread.sleep( 10000 ); } catch ( Exception ex ) { }
[*]
[*] for ( int i = 0; i < 10; i++ ) {
[*] boolean success = mcc.set( "" + i, "Hello!" );
[*] String result = (String)mcc.get( "" + i );
[*] System.out.println( String.format( "set( %d ): %s", i, success ) );
[*] System.out.println( String.format( "get( %d ): %s", i, result ) );
[*] }
[*] }
[*]}
以上代码大概做了这几件事情：
初始化一个连接池
新建一个memcached客户端
set一个key/value
get一个key，并且打印出value
这是我们实际应用中很常见的场景。
连接池的创建和初始化
连接池SockIOPool是非常重要的部分，它的好坏直接决定了客户端的性能。SockIOPool用一个HashMap持有多个连接池对象，连接池以名称作为标识，默认为"default"。看看
SockIOPool的getInstance方法就知道了。
Java代码
[*]public static SockIOPool getInstance() {
[*] return getInstance("default");
[*]}
[*]
[*]public static synchronized SockIOPool getInstance(String poolName) {
[*] if (pools.containsKey(poolName)) return pools.get(poolName);
[*]
[*] SockIOPool pool = new SockIOPool();
[*] pools.put(poolName, pool);
[*]
[*] return pool;
[*]}
连接池实例化完成后，还需要初始化，看看pool.initialize()做了什么：
Java代码
[*]
[*]
[*]public void initialize() {
[*] //这里以自身作为同步锁，防止被多次初始化
[*] synchronized (this) {
[*] // 如果已经被初始化了则终止初始化过程
[*] if (initialized && (buckets != null || consistentBuckets != null) && (availPool != null)&& (busyPool != null)) {
[*] log.error("++++ trying to initialize an already initialized pool");
[*] return;
[*] }
[*] <span style="color: #ff0000;">// 可用连接集合</span>
[*] availPool = new HashMap<String, Map<SockIO, Long>>(servers.length * initConn);
[*] //工作连接集合
[*] busyPool = new HashMap<String, Map<SockIO, Long>>(servers.length * initConn);
[*] // 不可用连接集合
[*] deadPool = new IdentityHashMap<SockIO, Integer>();
[*] hostDeadDur = new HashMap<String, Long>();
[*] hostDead = new HashMap<String, Date>();
[*] maxCreate = (poolMultiplier > minConn) ? minConn : minConn / poolMultiplier;
[*] if (log.isDebugEnabled()) {
[*] log.debug("++++ initializing pool with following settings:");
[*] log.debug("++++ initial size: " + initConn);
[*] log.debug("++++ min spare : " + minConn);
[*] log.debug("++++ max spare : " + maxConn);
[*] }
[*] if (servers == null || servers.length <= 0) {
[*] log.error("++++ trying to initialize with no servers");
[*] throw new IllegalStateException("++++ trying to initialize with no servers");
[*] }
[*] // initalize our internal hashing structures
[*] if (this.hashingAlg == CONSISTENT_HASH) populateConsistentBuckets();
[*] else populateBuckets();
[*] // mark pool as initialized
[*] this.initialized = true;
[*] // start maint thread
[*] if (this.maintSleep > 0) this.startMaintThread();
[*]}
[*]}
连接池的关闭
很简单，只是重置清空相关参数而已
Java代码
[*]public void shutDown() {
[*] synchronized (this) {
[*] if (log.isDebugEnabled()) log.debug("++++ SockIOPool shutting down...");
[*]
[*] if (maintThread != null && maintThread.isRunning()) {
[*] // stop the main thread
[*] stopMaintThread();
[*]
[*] // wait for the thread to finish
[*] while (maintThread.isRunning()) {
[*] if (log.isDebugEnabled()) log.debug("++++ waiting for main thread to finish run +++");
[*] try {
[*] Thread.sleep(500);
[*] } catch (Exception ex) {
[*] }
[*] }
[*] }
[*]
[*] if (log.isDebugEnabled()) log.debug("++++ closing all internal pools.");
[*] closePool(availPool);
[*] closePool(busyPool);
[*] availPool = null;
[*] busyPool = null;
[*] buckets = null;
[*] consistentBuckets = null;
[*] hostDeadDur = null;
[*] hostDead = null;
[*] maintThread = null;
[*] initialized = false;
[*] if (log.isDebugEnabled()) log.debug("++++ SockIOPool finished shutting down.");
[*] }
[*] }
连接池的自动平衡
SockIOPool的initialize()方法最后有这么一行代码
// start maint thread
if (this.maintSleep > 0) this.startMaintThread();
这是在初始化完成后，启动线程池平衡线程
Java代码
[*]protected void startMaintThread() {
[*] if (maintThread != null) {
[*] if (maintThread.isRunning()) {
[*] log.error("main thread already running");
[*] } else {
[*] maintThread.start();
[*] }
[*] } else {
[*] maintThread = new MaintThread(this);
[*] maintThread.setInterval(this.maintSleep);
[*] maintThread.start();
[*] }
[*]}
MaintThread的run方法
Java代码
[*]public void run() {
[*] this.running = true;
[*] while (!this.stopThread) {
[*] try {
[*] Thread.sleep(interval);
[*] // if pool is initialized, then
[*] // run the maintenance method on itself
[*] if (pool.isInitialized()) pool.selfMaint();
[*] } catch (Exception e) {
[*] break;
[*] }
[*] }
[*] this.running = false;
其实最终的平衡方法是SockIOPool.selfMaint()
Java代码
[*]protected void selfMaint() {
[*] if (log.isDebugEnabled()) log.debug("++++ Starting self maintenance....");
[*]
[*] // go through avail sockets and create sockets
[*] // as needed to maintain pool settings
[*] Map<String, Integer> needSockets = new HashMap<String, Integer>();
[*]
[*] synchronized (this) {
[*] // 先统计每个服务器实例的可用连接是否小于最小可用连接数
[*] for (Iterator<String> i = availPool.keySet().iterator(); i.hasNext();) {
[*] String host = i.next();
[*] Map<SockIO, Long> sockets = availPool.get(host);
[*]
[*] if (log.isDebugEnabled()) log.debug("++++ Size of avail pool for host (" + host + ") = "
[*] + sockets.size());
[*]
[*] // if pool is too small (n < minSpare)
[*] if (sockets.size() < minConn) {
[*] // need to create new sockets
[*] int need = minConn - sockets.size();
[*] needSockets.put(host, need);
[*] }
[*] }
[*] }
[*]
[*] // 如果小于最小可用连接数，则要新建增加可用连接
[*] Map<String, Set<SockIO>> newSockets = new HashMap<String, Set<SockIO>>();
[*]
[*] for (String host : needSockets.keySet()) {
[*] Integer need = needSockets.get(host);
[*]
[*] if (log.isDebugEnabled()) log.debug("++++ Need to create " + need + " new sockets for pool for host: "
[*] + host);
[*]
[*] Set<SockIO> newSock = new HashSet<SockIO>(need);
[*] for (int j = 0; j < need; j++) {
[*] SockIO socket = createSocket(host);
[*] if (socket == null) break;
[*] newSock.add(socket);
[*] }
[*] newSockets.put(host, newSock);
[*] }
[*]
[*] // synchronize to add and remove to/from avail pool
[*] // as well as clean up the busy pool (no point in releasing
[*] // lock here as should be quick to pool adjust and no
[*] // blocking ops here)
[*] synchronized (this) {
[*] //将新建的连接添加到可用连接集合里
[*] for (String host : newSockets.keySet()) {
[*] Set<SockIO> sockets = newSockets.get(host);
[*] for (SockIO socket : sockets)
[*] addSocketToPool(availPool, host, socket);
[*] }
[*]
[*] for (Iterator<String> i = availPool.keySet().iterator(); i.hasNext();) {
[*] String host = i.next();
[*] Map<SockIO, Long> sockets = availPool.get(host);
[*] if (log.isDebugEnabled()) log.debug("++++ Size of avail pool for host (" + host + ") = "
[*] + sockets.size());
[*]
[*] //如果可用连接超过了最大连接数，则要关闭一些
[*] if (sockets.size() > maxConn) {
[*] // need to close down some sockets
[*] int diff = sockets.size() - maxConn;
[*] int needToClose = (diff <= poolMultiplier) ? diff : (diff) / poolMultiplier;
[*]
[*] if (log.isDebugEnabled()) log.debug("++++ need to remove " + needToClose
[*] + " spare sockets for pool for host: " + host);
[*]
[*] for (Iterator<SockIO> j = sockets.keySet().iterator(); j.hasNext();) {
[*] if (needToClose <= 0) break;
[*]
[*] // remove stale entries
[*] SockIO socket = j.next();
[*] long expire = sockets.get(socket).longValue();
[*]
[*] // 这里回收可用连接池的闲置连接,连接设置到可用连接池里时,expire设置为当前时间。如果 (expire + maxIdle) < System.currentTimeMillis()为true，则表
[*]明，该连接在可用连接池呆得太久了，需要回收
[*] if ((expire + maxIdle) < System.currentTimeMillis()) {
[*] if (log.isDebugEnabled()) log.debug("+++ removing stale entry from pool as it is past its idle timeout and pool is over max spare");
[*]
[*] // remove from the availPool
[*] deadPool.put(socket, ZERO);
[*] j.remove();
[*] needToClose--;
[*] }
[*] }
[*] }
[*] }
[*]
[*] //清理正在工作的连接集合
[*] for (Iterator<String> i = busyPool.keySet().iterator(); i.hasNext();) {
[*] String host = i.next();
[*] Map<SockIO, Long> sockets = busyPool.get(host);
[*] if (log.isDebugEnabled()) log.debug("++++ Size of busy pool for host (" + host + ")= "
[*] + sockets.size());
[*] // loop through all connections and check to see if we have any hung connections
[*] for (Iterator<SockIO> j = sockets.keySet().iterator(); j.hasNext();) {
[*] // remove stale entries
[*] SockIO socket = j.next();
[*] long hungTime = sockets.get(socket).longValue();
[*] //如果工作时间超过maxBusyTime，则也要回收掉，超过maxBusyTime，可能是服务器响应时间过长
[*] if ((hungTime + maxBusyTime) < System.currentTimeMillis()) {
[*] log.error("+++ removing potentially hung connection from busy pool ... socket in pool for "
[*] + (System.currentTimeMillis() - hungTime) + "ms");
[*]
[*] // remove from the busy pool
[*] deadPool.put(socket, ZERO);
[*] j.remove();
[*] }
[*] }
[*] }
[*] }
[*]
[*] // 最后清理不可用连接集合
[*] Set<SockIO> toClose;
[*] synchronized (deadPool) {
[*] toClose = deadPool.keySet();
[*] deadPool = new IdentityHashMap<SockIO, Integer>();
[*] }
[*]
[*] for (SockIO socket : toClose) {
[*] try {
[*] socket.trueClose(false);
[*] } catch (Exception ex) {
[*] log.error("++++ failed to close SockIO obj from deadPool");
[*] log.error(ex.getMessage(), ex);
[*] }
[*]
[*] socket = null;
[*] }
[*]
[*] if (log.isDebugEnabled()) log.debug("+++ ending self maintenance.");
[*] }
key的服务器端分布
初始化方法其实就是根据每个服务器的权重，建立一个服务器地址集合，如果选择了一致性哈希，则对服务器地址进行一致性哈希分布，一致性哈希算法比较简单，如果不了解的同学，可以
自行google一下，initialize() 方法里有这段代码：
//一致性哈希
Java代码
[*]if (this.hashingAlg == CONSISTENT_HASH){
[*]populateConsistentBuckets();
[*]}else populateBuckets();
看看populateConsistentBuckets()方法
// 用一致性哈希算法将服务器分布在一个2的32次方的环里，服务器的分布位置<=servers.length*40*4
Java代码
[*]private void populateConsistentBuckets() {
[*] if (log.isDebugEnabled()) log.debug("++++ initializing internal hashing structure for consistent hashing");
[*]
[*] // store buckets in tree map
[*] this.consistentBuckets = new TreeMap<Long, String>();
[*] MessageDigest md5 = MD5.get();
[*] if (this.totalWeight <= 0 && this.weights != null) {
[*] for (int i = 0; i < this.weights.length; i++)
[*] this.totalWeight += (this.weights == null) ? 1 : this.weights;
[*] } else if (this.weights == null) {
[*] this.totalWeight = this.servers.length;
[*] }
[*]
[*] for (int i = 0; i < servers.length; i++) {
[*] int thisWeight = 1;
[*] if (this.weights != null && this.weights != null) thisWeight = this.weights;
[*]
[*] //这个值永远小于40 * this.servers.length,因为thisWeight/totalWeight永远小于1
Java代码
[*] double factor = Math.floor(((double) (40 * this.servers.length * thisWeight)) / (double) this.totalWeight);
[*]
[*]//服务器的分布位置为factor*4,factor<=40*this.servers.length,所以服务器的分布位置& lt;=40*this.servers.length*4。
[*]for (long j = 0; j < factor; j++) {
[*] //md5值的二进制数组为16位
[*] byte[] d = md5.digest((servers + "-" + j).getBytes());
[*] //16位二进制数组每4位为一组，每组第4个值左移24位，第三个值左移16位，第二个值左移8位，第一个值不移位。进行或运算，得到一个小于2的32 次方的long值。
[*] for (int h = 0; h < 4; h++) {
[*] Long k = ((long) (d & 0xFF) << 24) | ((long) (d & 0xFF) << 16)
[*] | ((long) (d & 0xFF) << 8) | ((long) (d & 0xFF));
[*] consistentBuckets.put(k, servers);
[*] if (log.isDebugEnabled()) log.debug("++++ added " + servers + " to server bucket");
[*] }
[*] }
[*]
[*] // create initial connections
[*] if (log.isDebugEnabled()) log.debug("+++ creating initial connections (" + initConn + ") for host: "
[*] + servers);
[*]
[*] //创建连接
[*] for (int j = 0; j < initConn; j++) {
[*] SockIO socket = createSocket(servers);
[*] if (socket == null) {
[*] log.error("++++ failed to create connection to: " + servers + " -- only " + j + " created.");
[*] break;
[*] }
[*]
[*] //添加到可用连接池
[*] addSocketToPool(availPool, servers, socket);
[*] if (log.isDebugEnabled()) log.debug("++++ created and added socket: " + socket.toString()
[*] + " for host " + servers);
[*] }
[*]}
如果不是一致性哈希，则只是普通分布，很简单，只是根据权重将服务器地址放入buckets这个List里
Java代码
[*]private void populateBuckets() {
[*] if (log.isDebugEnabled()) log.debug("++++ initializing internal hashing structure for consistent hashing");
[*]
[*] // store buckets in tree map
[*] this.buckets = new ArrayList<String>();
[*]
[*] for (int i = 0; i < servers.length; i++) {
[*] if (this.weights != null && this.weights.length > i) {
[*] for (int k = 0; k < this.weights.intValue(); k++) {
[*] this.buckets.add(servers);
[*] if (log.isDebugEnabled()) log.debug("++++ added " + servers + " to server bucket");
[*] }
[*] } else {
[*] this.buckets.add(servers);
[*] if (log.isDebugEnabled()) log.debug("++++ added " + servers + " to server bucket");
[*] }
[*]
[*] // create initial connections
[*] if (log.isDebugEnabled()) log.debug("+++ creating initial connections (" + initConn + ") for host: "
[*] + servers);
[*]
[*] for (int j = 0; j < initConn; j++) {
[*] SockIO socket = createSocket(servers);
[*] if (socket == null) {
[*] log.error("++++ failed to create connection to: " + servers + " -- only " + j + " created.");
[*] break;
[*] }
[*]
[*] //新建连接后，加入到可用连接集合里
[*] addSocketToPool(availPool, servers, socket);
[*] if (log.isDebugEnabled()) log.debug("++++ created and added socket: " + socket.toString()
[*] + " for host " + servers);
[*] }
[*] }
[*] }
如何创建socket连接
在上面的private void populateBuckets()方法里，createSocket(servers)是创建到服务器的连接，看看这个方法
Java代码
[*]protected SockIO createSocket(String host) {
[*]SockIO socket = null;
[*]//hostDeadLock是一个可重入锁,它的变量声明为
[*]
[*]
[*]private final ReentrantLock hostDeadLock = new ReentrantLock();
[*]hostDeadLock.lock();
[*]try {
[*]//hostDead.containsKey(host)为true表示曾经连接过该服务器，但没有成功。
[*]//hostDead是一个HashMap，key为服务器地址，value为当时连接不成功的时间
[*]//hostDeadDur是一个HashMap，key为服务器地址，value为设置的重试间隔时间
[*]
[*] if (failover && failback && hostDead.containsKey(host) && hostDeadDur.containsKey(host)) {
[*] Date store = hostDead.get(host);
[*] long expire = hostDeadDur.get(host).longValue();
[*]
[*] if ((store.getTime() + expire) > System.currentTimeMillis()) return null;
[*] }
[*] } finally {
[*] hostDeadLock.unlock();
[*]}
[*]
[*]
[*]try {
[*] socket = new SockIO(this, host, this.socketTO, this.socketConnectTO, this.nagle);
[*] if (!socket.isConnected()) {
[*] log.error("++++ failed to get SockIO obj for: " + host + " -- new socket is not connected");
[*] deadPool.put(socket, ZERO);
[*] socket = null;
[*] }
[*] } catch (Exception ex) {
[*] log.error("++++ failed to get SockIO obj for: " + host);
[*] log.error(ex.getMessage(), ex);
[*] socket = null;
[*] }
[*]
[*]// if we failed to get socket, then mark
[*]// host dead for a duration which falls off
[*]hostDeadLock.lock();
[*]try {
[*] //到了这里,socket仍然为null，说明这个server悲剧了，无法和它创建连接，则要把该server丢到不可用的主机集合里
[*] if (socket == null) {
[*] Date now = new Date();
[*] hostDead.put(host, now);
[*]
[*] //如果上次就不可用了，到期了仍然不可用，就要这次的不可用时间设为上次的2倍，否则初始时长为1000ms
[*] long expire = (hostDeadDur.containsKey(host)) ? (((Long) hostDeadDur.get(host)).longValue() * 2) : 1000;
[*]
[*] if (expire > MAX_RETRY_DELAY) expire = MAX_RETRY_DELAY;
[*]
[*] hostDeadDur.put(host, new Long(expire));
[*] if (log.isDebugEnabled()) log.debug("++++ ignoring dead host: " + host + " for " + expire + " ms");
[*]
[*] // 既然这个host都不可用了，那与它的所有连接当然要从可用连接集合"availPool"里删除掉
[*] clearHostFromPool(availPool, host);
[*] } else {
[*] if (log.isDebugEnabled()) log.debug("++++ created socket (" + socket.toString() + ") for host: " + host);
[*] //连接创建成功，如果上次不成功，那么这次要把该host从不可用主机集合里删除掉
[*] if (hostDead.containsKey(host) || hostDeadDur.containsKey(host)) {
[*] hostDead.remove(host);
[*] hostDeadDur.remove(host);
[*] }
[*] }
[*] } finally {
[*] hostDeadLock.unlock();
[*] }
[*]
[*] return socket;
[*] }
SockIO构造函数
Java代码
[*]public SockIO(SockIOPool pool, String host, int timeout, int connectTimeout, boolean noDelay)
[*] throws IOException,
[*] UnknownHostException {
[*] this.pool = pool;
[*] String[] ip = host.split(":");
[*] // get socket: default is to use non-blocking connect
[*] sock = getSocket(ip, Integer.parseInt(ip), connectTimeout);
[*] if (timeout >= 0) this.sock.setSoTimeout(timeout);
[*] // testing only
[*] sock.setTcpNoDelay(noDelay);
[*] // wrap streams
[*] in = new DataInputStream(new BufferedInputStream(sock.getInputStream()));
[*] out = new BufferedOutputStream(sock.getOutputStream());
[*] this.host = host;
[*]}
getSocket方法
Java代码
[*]protected static Socket getSocket(String host, int port, int timeout) throws IOException {
[*] SocketChannel sock = SocketChannel.open();
[*] sock.socket().connect(new InetSocketAddress(host, port), timeout);
[*] return sock.socket();
[*] }
可以看到，socket连接是用nio方式创建的。
新建MemcachedClient
MemcachedClient mcc = new MemcachedClient();新建了一个memcached客户端，看看构造函数，没作什么，只是设置参数而已。
Java代码
[*]/**
[*]* Creates a new instance of MemCachedClient.
[*]*/
[*] public MemcachedClient() {
[*] init();
[*] }
[*]
[*]
[*] private void init() {
[*] this.sanitizeKeys = true;
[*] this.primitiveAsString= false;
[*] this.compressEnable = true;
[*] this.compressThreshold= COMPRESS_THRESH;
[*] this.defaultEncoding = "UTF-8";
[*] this.poolName = ( this.poolName == null ) ? "default" : this.poolName;
[*]
[*] // get a pool instance to work with for the life of this instance
[*] this.pool = SockIOPool.getInstance( poolName );
[*] }
set方法如何工作
到此memcached客户端初始化工作完成。再回到测试类TestMemcached，看看for循环里的
boolean success = mcc.set( ""+ i, "Hello!" );
String result = (String)mcc.get( "" + i );
初始化后，就可以set，get了。看看set是怎么工作的。
Java代码
[*]/**
[*] * Stores data on the server; only the key and the value are specified.
[*] *
[*] * @param key key to store data under
[*] * @param value value to store
[*] * @return true, if the data was successfully stored
[*] */
[*] public boolean set( String key, Object value ) {
[*] return set( "set", key, value, null, null, primitiveAsString );
[*] }
[*]
[*]
[*] //这个set方法比较长
[*] private boolean set( String cmdname, String key, Object value, Date expiry, Integer hashCode, boolean asString ) {
[*] if ( cmdname == null || cmdname.trim().equals( "" ) || key == null ) {
[*] log.error( "key is null or cmd is null/empty for set()" );
[*] return false;
[*] }
[*]
[*] try {
[*] key = sanitizeKey( key );
[*] }
[*] catch ( UnsupportedEncodingException e ) {
[*] // if we have an errorHandler, use its hook
[*] if ( errorHandler != null )
[*] errorHandler.handleErrorOnSet( this, e, key );
[*] log.error( "failed to sanitize your key!", e );
[*] return false;
[*] }
[*]
[*] if ( value == null ) {
[*] log.error( "trying to store a null value to cache" );
[*] return false;
[*] }
[*]
[*] // get SockIO obj
[*] SockIOPool.SockIO sock = pool.getSock( key, hashCode );
[*]
[*] if ( sock == null ) {
[*] if ( errorHandler != null )
[*] errorHandler.handleErrorOnSet( this, new IOException( "no socket to server available" ), key );
[*] return false;
[*] }
[*]
[*] if ( expiry == null )
[*] expiry = new Date(0);
[*]
[*] // store flags
[*] int flags = 0;
[*]
[*] // byte array to hold data
[*] byte[] val;
[*]
[*] //这些类型自己序列化，否则由java序列化处理
[*] if ( NativeHandler.isHandled( value ) ) {
[*] if ( asString ) {
[*] //如果是字符串，则直接getBytes
[*] try {
[*] if ( log.isInfoEnabled() )
[*] log.info( "++++ storing data as a string for key: " + key + " for class: " + value.getClass().getName() );
[*] val = value.toString().getBytes( defaultEncoding );
[*] }
[*] catch ( UnsupportedEncodingException ue ) {
[*] // if we have an errorHandler, use its hook
[*] if ( errorHandler != null )
[*] errorHandler.handleErrorOnSet( this, ue, key );
[*] log.error( "invalid encoding type used: " + defaultEncoding, ue );
[*] sock.close();
[*] sock = null;
[*] return false;
[*] }
[*] }
[*] else {
[*] try {
[*] if ( log.isInfoEnabled() )
[*] log.info( "Storing with native handler..." );
[*] flags |= NativeHandler.getMarkerFlag( value );
[*] val = NativeHandler.encode( value );
[*] }
[*] catch ( Exception e ) {
[*] // if we have an errorHandler, use its hook
[*] if ( errorHandler != null )
[*] errorHandler.handleErrorOnSet( this, e, key );
[*] log.error( "Failed to native handle obj", e );
[*]
[*] sock.close();
[*] sock = null;
[*] return false;
[*] }
[*] }
[*] }
[*] else {
[*] // 否则用java的序列化
[*] try {
[*] if ( log.isInfoEnabled() )
[*] log.info( "++++ serializing for key: " + key + " for class: " + value.getClass().getName() );
[*] ByteArrayOutputStream bos = new ByteArrayOutputStream();
[*] (new ObjectOutputStream( bos )).writeObject( value );
[*] val = bos.toByteArray();
[*] flags |= F_SERIALIZED;
[*] }
[*] catch ( IOException e ) {
[*] // if we have an errorHandler, use its hook
[*] if ( errorHandler != null )
[*] errorHandler.handleErrorOnSet( this, e, key );
[*]
[*] // if we fail to serialize, then
[*] // we bail
[*] log.error( "failed to serialize obj", e );
[*] log.error( value.toString() );
[*]
[*] // return socket to pool and bail
[*] sock.close();
[*] sock = null;
[*] return false;
[*] }
[*] }
[*]
[*] //压缩内容
[*] if ( compressEnable && val.length > compressThreshold ) {
[*] try {
[*] if ( log.isInfoEnabled() ) {
[*] log.info( "++++ trying to compress data" );
[*] log.info( "++++ size prior to compression: " + val.length );
[*] }
[*] ByteArrayOutputStream bos = new ByteArrayOutputStream( val.length );
[*] GZIPOutputStream gos = new GZIPOutputStream( bos );
[*] gos.write( val, 0, val.length );
[*] gos.finish();
[*] gos.close();
[*]
[*] // store it and set compression flag
[*] val = bos.toByteArray();
[*] flags |= F_COMPRESSED;
[*]
[*] if ( log.isInfoEnabled() )
[*] log.info( "++++ compression succeeded, size after: " + val.length );
[*] }
[*] catch ( IOException e ) {
[*] // if we have an errorHandler, use its hook
[*] if ( errorHandler != null )
[*] errorHandler.handleErrorOnSet( this, e, key );
[*] log.error( "IOException while compressing stream: " + e.getMessage() );
[*] log.error( "storing data uncompressed" );
[*] }
[*] }
[*]
[*] // now write the data to the cache server
[*] try {
[*] //按照memcached协议组装命令
[*] String cmd = String.format( "%s %s %d %d %d\r\n", cmdname, key, flags, (expiry.getTime() / 1000), val.length );
[*] sock.write( cmd.getBytes() );
[*] sock.write( val );
[*] sock.write( "\r\n".getBytes() );
[*] sock.flush();
[*]
[*] // get result code
[*] String line = sock.readLine();
[*] if ( log.isInfoEnabled() )
[*] log.info( "++++ memcache cmd (result code): " + cmd + " (" + line + ")" );
[*]
[*] if ( STORED.equals( line ) ) {
[*] if ( log.isInfoEnabled() )
[*] log.info("++++ data successfully stored for key: " + key );
[*] sock.close();
[*] sock = null;
[*] return true;
[*] }
[*] else if ( NOTSTORED.equals( line ) ) {
[*] if ( log.isInfoEnabled() )
[*] log.info( "++++ data not stored in cache for key: " + key );
[*] }
[*] else {
[*] log.error( "++++ error storing data in cache for key: " + key + " -- length: " + val.length );
[*] log.error( "++++ server response: " + line );
[*] }
[*] }
[*] catch ( IOException e ) {
[*]
[*] // if we have an errorHandler, use its hook
[*] if ( errorHandler != null )
[*] errorHandler.handleErrorOnSet( this, e, key );
[*]
[*] // exception thrown
[*] log.error( "++++ exception thrown while writing bytes to server on set" );
[*] log.error( e.getMessage(), e );
[*]
[*] try {
[*] sock.trueClose();
[*] }
[*] catch ( IOException ioe ) {
[*] log.error( "++++ failed to close socket : " + sock.toString() );
[*] }
[*]
[*] sock = null;
[*] }
[*]
[*] //用完了，就要回收哦，sock.close()不是真正的关闭，只是放入到可用连接集合里。
[*] if ( sock != null ) {
[*] sock.close();
[*] sock = null;
[*] }
[*] return false;
[*] }
通过set方法向服务器设置key和value，涉及到以下几个点
数据的压缩和序列化 （如果是get方法，则和set方法基本是相反的）
为key分配服务器 对于一些常用类型，采用自定义的序列化，具体要看NativeHander.java，这个类比较简单，有兴趣可以自己看看
Java代码
[*]public static boolean isHandled( Object value ) {
[*] return (
[*] value instanceof Byte ||
[*] value instanceof Boolean ||
[*] value instanceof Integer ||
[*] value instanceof Long ||
[*] value instanceof Character ||
[*] value instanceof String ||
[*] value instanceof StringBuffer ||
[*] value instanceof Float ||
[*] value instanceof Short ||
[*] value instanceof Double ||
[*] value instanceof Date ||
[*] value instanceof StringBuilder ||
[*] value instanceof byte[]
[*] )
[*] ? true
[*] : false;
[*] }
其他类型则用java的默认序列化
为key选择服务器
SockIOPool.SockIO sock = pool.getSock( key, hashCode );就是为key选择服务器
Java代码
[*]public SockIO getSock(String key, Integer hashCode) {
[*] if (log.isDebugEnabled()) log.debug("cache socket pick " + key + " " + hashCode);
[*] if (!this.initialized) {
[*] log.error("attempting to get SockIO from uninitialized pool!");
[*] return null;
[*] }
[*]
[*] // if no servers return null
[*] if ((this.hashingAlg == CONSISTENT_HASH && consistentBuckets.size() == 0)
[*] || (buckets != null && buckets.size() == 0)) return null;
[*]
[*] // if only one server, return it
[*] if ((this.hashingAlg == CONSISTENT_HASH && consistentBuckets.size() == 1)
[*] || (buckets != null && buckets.size() == 1)) {
[*] SockIO sock = (this.hashingAlg == CONSISTENT_HASH) ? getConnection(consistentBuckets.get(consistentBuckets.firstKey())) : getConnection(buckets.get(0));
[*] if (sock != null && sock.isConnected()) {
[*] if (aliveCheck) {//健康状态检查
[*]
[*] if (!sock.isAlive()) {
[*] sock.close();
[*] try {
[*] sock.trueClose();//有问题，真的关闭socket
[*]
[*] } catch (IOException ioe) {
[*] log.error("failed to close dead socket");
[*] }
[*] sock = null;
[*] }
[*] }
[*] } else {//连接不正常，放入不可用连接集合里
[*] if (sock != null) {
[*] deadPool.put(sock, ZERO);
[*] sock = null;
[*] }
[*] }
[*]
[*] return sock;
[*] }
[*]
[*] Set<String> tryServers = new HashSet<String>(Arrays.asList(servers));
[*] // get initial bucket
[*] long bucket = getBucket(key, hashCode);
[*] String server = (this.hashingAlg == CONSISTENT_HASH) ? consistentBuckets.get(bucket) : buckets.get((int) bucket);
[*]
[*] while (!tryServers.isEmpty()) {
[*] // try to get socket from bucket
[*] SockIO sock = getConnection(server);
[*] if (log.isDebugEnabled()) log.debug("cache choose " + server + " for " + key);
[*] if (sock != null && sock.isConnected()) {
[*] if (aliveCheck) {
[*] if (sock.isAlive()) {
[*] return sock;
[*] } else {
[*] sock.close();
[*] try {
[*] sock.trueClose();
[*] } catch (IOException ioe) {
[*] log.error("failed to close dead socket");
[*] }
[*] sock = null;
[*] }
[*] } else {
[*] return sock;
[*] }
[*] } else {
[*] if (sock != null) {
[*] deadPool.put(sock, ZERO);
[*] sock = null;
[*] }
[*] }
[*]
[*] // if we do not want to failover, then bail here
[*] if (!failover) return null;
[*]
[*] // log that we tried
[*] tryServers.remove(server);
[*]
[*] if (tryServers.isEmpty()) break;
[*] //注意哦，下面是failover机制
[*] int rehashTries = 0;
[*] while (!tryServers.contains(server)) {
[*] String newKey = String.format("%s%s", rehashTries, key);
[*] if (log.isDebugEnabled()) log.debug("rehashing with: " + newKey);
[*]
[*] bucket = getBucket(newKey, null);
[*] server = (this.hashingAlg == CONSISTENT_HASH) ? consistentBuckets.get(bucket) : buckets.get((int) bucket);
[*] rehashTries++;
[*] }
[*] }
[*] return null;
[*] }
下面这个方法是真正的从服务器获取连接
Java代码
[*]public SockIO getConnection(String host) {
[*] if (!this.initialized) {
[*] log.error("attempting to get SockIO from uninitialized pool!");
[*] return null;
[*] }
[*]
[*] if (host == null) return null;
[*]
[*] synchronized (this) {
[*] // if we have items in the pool
[*] // then we can return it
[*] if (availPool != null && !availPool.isEmpty()) {
[*] // take first connected socket
[*] Map<SockIO, Long> aSockets = availPool.get(host);
[*] if (aSockets != null && !aSockets.isEmpty()) {
[*] for (Iterator<SockIO> i = aSockets.keySet().iterator(); i.hasNext();) {
[*] SockIO socket = i.next();
[*] if (socket.isConnected()) {
[*] if (log.isDebugEnabled()) log.debug("++++ moving socket for host (" + host
[*] + ") to busy pool ... socket: " + socket);
[*] // remove from avail pool
[*] i.remove();
[*] // add to busy pool
[*] addSocketToPool(busyPool, host, socket);
[*] // return socket
[*] return socket;
[*] } else {
[*] // add to deadpool for later reaping
[*] deadPool.put(socket, ZERO);
[*] // remove from avail pool
[*] i.remove();
[*] }
[*] }
[*] }
[*] }
[*] }
[*]
[*] // create one socket -- let the maint thread take care of creating more
[*] SockIO socket = createSocket(host);
[*] if (socket != null) {
[*] synchronized (this) {
[*] addSocketToPool(busyPool, host, socket);
[*] }
[*] }
[*] return socket;
[*] }
[*]
[*]
failover和failback
这两者都是发生在获取可用连接这个环节。
failover，如果为key选择的服务器不可用，则对key重新哈希选择下一个服务器，详见getSock方法的末尾。
failback，用一个hashmap存储连接失败的服务器和对应的失效持续时间，每次获取连接时，都探测是否到了重试时间。
页:
[1]