Codis源码解析—

我们在java项目里面连接已经搭建好的Codis集群时，需要用到其java客户端——Jodis。这一篇我们就来看看Jodis是如何操作对Codis集群进行操作的。

import io.codis.jodis.JedisResourcePool;
import io.codis.jodis.RoundRobinJedisPool;
import redis.clients.jedis.Jedis;
/*** @author wujiang* @version 1.0.0* @date 2017/7/12*/
public class CodisDemo {public static void main(String[] args) {JedisResourcePool jedisPool = RoundRobinJedisPool.create().curatorClient("10.0.2.15:2181", 30000).zkProxyDir("/jodis/codis-wujiang").build();try (Jedis jedis = jedisPool.getResource()) {//省略代码}}
}

如果在运行中遇到报错

Redis.clients.jedis.exceptions.JedisException: Proxy list empty

可以参考之前的一篇博客Jodis报错- JedisException- Proxy list empty进行解决。

Jodis中最重要的一个类就是RoundRobinJedisPool。首先来看看这个类的继承结构和方法

在RoundRobinJedisPool.class中有一个内部类Builder，是用来与zk集群进行连接的。在build之前，一直都是在设置Builder的属性，例如将Builder的connectionTimeoutMs和soTimeoutMs分别设置为2000，database设置为0，传入zk地址和路径等等。然后会调用下面的build方法

public static final class Builder {private CuratorFramework curatorClient;private boolean closeCurator;private String zkProxyDir;private String zkAddr;private int zkSessionTimeoutMs;private JedisPoolConfig poolConfig;private int connectionTimeoutMs;private int soTimeoutMs;private String password;private int database;private String clientName;.public RoundRobinJedisPool build() {this.validate();return new RoundRobinJedisPool(this.curatorClient, this.closeCurator, this.zkProxyDir, this.poolConfig, this.connectionTimeoutMs, this.soTimeoutMs, this.password, this.database, this.clientName, null);}.private void validate() {//首先检查zkProxyDir和zkAddr是否为空Preconditions.checkNotNull(this.zkProxyDir, "zkProxyDir can not be null");//初始化curatorClient并启动if (this.curatorClient == null) {Preconditions.checkNotNull(this.zkAddr, "zk client can not be null");this.curatorClient = CuratorFrameworkFactory.builder().connectString(this.zkAddr).sessionTimeoutMs(this.zkSessionTimeoutMs).retryPolicy(new BoundedExponentialBackoffRetryUntilElapsed(100, 30000, -1L)).build();this.curatorClient.start();this.closeCurator = true;} else if (this.curatorClient.getState() == CuratorFrameworkState.LATENT) {this.curatorClient.start();}if (this.poolConfig == null) {this.poolConfig = new JedisPoolConfig();}}
}

初始化的CuratorClient如下所示，curator-client组件可以作为zookeeper client来使用,它提供了zk实例创建/重连机制等

最关键的是后面创建RoundRobinJedisPool这一步。

private RoundRobinJedisPool(CuratorFramework curatorClient, boolean closeCurator, String zkProxyDir, JedisPoolConfig poolConfig, int connectionTimeoutMs, int soTimeoutMs, String password, int database, String clientName) {//新建ImmutableList<PooledObject>，每个PooledObject包含了proxy addr以及jedisPoolthis.pools = ImmutableList.of();this.nextIdx = new AtomicInteger(-1);this.poolConfig = poolConfig;this.connectionTimeoutMs = connectionTimeoutMs;this.soTimeoutMs = soTimeoutMs;this.password = password;this.database = database;this.clientName = clientName;this.curatorClient = curatorClient;//truethis.closeCurator = closeCurator;this.watcher = new PathChildrenCache(curatorClient, zkProxyDir, true);//监听zkProxyDir下面的变化，也就是当集群中新加入proxy或者有proxy宕机之后，都会由watcher得到该消息this.watcher.getListenable().addListener(new PathChildrenCacheListener() {private void logEvent(PathChildrenCacheEvent event) {StringBuilder msg = new StringBuilder("Receive child event: ");msg.append("type=").append(event.getType());ChildData data = event.getData();if (data != null) {msg.append(", path=").append(data.getPath());msg.append(", stat=").append(data.getStat());if (data.getData() != null) {msg.append(", bytes length=").append(data.getData().length);} else {msg.append(", no bytes");}} else {msg.append(", no data");}RoundRobinJedisPool.LOG.info(msg.toString());}public void childEvent(CuratorFramework client, PathChildrenCacheEvent event) throws Exception {this.logEvent(event);//如果zk下监听事件类型为添加、更新、删除（这是通过静态代码块注入的），就重置poolif (RoundRobinJedisPool.RESET_TYPES.contains(event.getType())) {RoundRobinJedisPool.this.resetPools();}}});try {//以BUILD_INITIAL_CACHE模式启动watcherthis.watcher.start(StartMode.BUILD_INITIAL_CACHE);} catch (Exception var11) {this.close();throw new JedisException(var11);}this.resetPools();
}
//启动watcher的方法
public void rebuild() throws Exception {Preconditions.checkState(!this.executorService.isShutdown(), "cache has been closed");this.ensurePath();this.clear();///jodis/codis-wujiang下面的proxy，本例中只有一个proxy-00e6b8c9d5cc40ed5f81ea515b2b7695List<String> children = (List)this.client.getChildren().forPath(this.path);Iterator var2 = children.iterator();while(var2.hasNext()) {String child = (String)var2.next();///jodis/codis-wujiang/proxy-00e6b8c9d5cc40ed5f81ea515b2b7695String fullPath = ZKPaths.makePath(this.path, child);this.internalRebuildNode(fullPath);if (this.rebuildTestExchanger != null) {this.rebuildTestExchanger.exchange(new Object());}}this.offerOperation(new RefreshOperation(this, PathChildrenCache.RefreshMode.FORCE_GET_DATA_AND_STAT));}

下一步，resetPool，根据zk中的proxy以及对应的jedis变化，更新集群中的redisPool。这样pool中永远都有每个proxy以及proxy中对应的jedisPool。

注意，下面的addr2Pool是RoundRobinJedisPool当前的pool，从zk当前的数据中取出现在的所有proxy，从addr2Pool中删除，并放入builder中。如果删除的时候为null，证明原来的pool中并没有这个proxy连接，于是新建一个并放到builder中。最后的RoundRobinJedisPool.pool相当于是builder.build出来的。再将addr2Pool中剩余的proxy连接关闭（这里用了一个trick，JedisPool实际上是proxy连接）

private static final class PooledObject {//addr是proxy的19000端口地址public final String addr;public final JedisPool pool;public PooledObject(String addr, JedisPool pool) {this.addr = addr;this.pool = pool;}
}private void resetPools() {ImmutableList<RoundRobinJedisPool.PooledObject> pools = this.pools;Map<String, RoundRobinJedisPool.PooledObject> addr2Pool = Maps.newHashMapWithExpectedSize(pools.size());UnmodifiableIterator var3 = pools.iterator();while(var3.hasNext()) {RoundRobinJedisPool.PooledObject pool = (RoundRobinJedisPool.PooledObject)var3.next();addr2Pool.put(pool.addr, pool);}com.google.common.collect.ImmutableList.Builder<RoundRobinJedisPool.PooledObject> builder = ImmutableList.builder();Iterator var14 = this.watcher.getCurrentData().iterator();while(var14.hasNext()) {ChildData childData = (ChildData)var14.next();try {//封装了proxy addr（19000端口）以及state（是否在线）CodisProxyInfo proxyInfo = (CodisProxyInfo)MAPPER.readValue(childData.getData(), CodisProxyInfo.class);if ("online".equals(proxyInfo.getState())) {String addr = proxyInfo.getAddr();RoundRobinJedisPool.PooledObject pool = (RoundRobinJedisPool.PooledObject)addr2Pool.remove(addr);//第一次进来的时候，pool为null，会执行下面的pool的构造方法if (pool == null) {LOG.info("Add new proxy: " + addr);String[] hostAndPort = addr.split(":");String host = hostAndPort[0];int port = Integer.parseInt(hostAndPort[1]);pool = new RoundRobinJedisPool.PooledObject(addr, new JedisPool(this.poolConfig, host, port, this.connectionTimeoutMs, this.soTimeoutMs, this.password, this.database, this.clientName, false, (SSLSocketFactory)null, (SSLParameters)null, (HostnameVerifier)null));}builder.add(pool);}} catch (Throwable var12) {LOG.warn("parse " + childData.getPath() + " failed", var12);}}this.pools = builder.build();var14 = addr2Pool.values().iterator();while(var14.hasNext()) {RoundRobinJedisPool.PooledObject pool = (RoundRobinJedisPool.PooledObject)var14.next();LOG.info("Remove proxy: " + pool.addr);pool.pool.close();}}

创建好的RoundRobinJedisPool.pools如下所示

当一个pool准备好，下一步我们的操作就是从pool中取出相应的jedis实例，并进行相关操作。这个pool里面只有服务正常的proxy，error的proxy会从zk被剔除掉，详见 Codis源码解析——proxy添加到集群

public Jedis getResource() {ImmutableList<RoundRobinJedisPool.PooledObject> pools = this.pools;if (pools.isEmpty()) {throw new JedisException("Proxy list empty");} else {int current;int next;do {//nextIdx初始值是-1current = this.nextIdx.get();//pools.size取决于集群中有多少个proxy，可以看到，负载均衡算法采取的是轮询next = current >= pools.size() - 1 ? 0 : current + 1;} while(!this.nextIdx.compareAndSet(current, next));return ((RoundRobinJedisPool.PooledObject)pools.get(next)).pool.getResource();}
}

Jodis首先让你本地的java程序通过zookeeper（或者etcd）连接到proxy，并监听proxy的变化，因为可能根据需要对proxy做水平扩容。监听过程中，对由PooledObject组成的pool进行刷新，然后每次需要对codis集群进行操作的时候，都按照轮询负载均衡算法从pool中取出一个jedis实例进行操作。

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