Codis源码解析——Jodis

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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

这里写图片描述

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

这里写图片描述

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jedisPool    this.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;    //true    this.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pool            if (RoundRobinJedisPool.RESET_TYPES.contains(event.getType())) {                RoundRobinJedisPool.this.resetPools();            }        }    });    try {        //以BUILD_INITIAL_CACHE模式启动watcher        this.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-00e6b8c9d5cc40ed5f81ea515b2b7695    List<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-00e6b8c9d5cc40ed5f81ea515b2b7695        String 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。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

这里写图片描述

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-1            current = 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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