Codis源码解析——Jodis
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，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 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。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.PooledObject> pools = this.pools;
Map.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.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 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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http://blog.csdn.net/antony9118/article/details/77776072