ServiceStack.Redis的源码分析

前几天在生产环境上redis创建连接方面的故障，分析过程中对ServiceStack.Redis的连接创建和连接池机制有了进一步了解。问题分析结束后，通过此问题系统的将学习到的知识点整理出来。

从连接池获取RedisClient的流程

业务程序中通过PooledRedisClientManager对象的GetClient()方法获取客户端对象，就以此处的源码作为入口：

查看代码

public IRedisClient GetClient()        {            RedisClient redisClient = null;            DateTime now = DateTime.Now;            for (; ; )            {                if (!this.deactiveClientQueue.TryPop(out redisClient))                {                    if (this.redisClientSize >= this.maxRedisClient)                    {                        Thread.Sleep(3);                        if (this.PoolTimeout != null && (DateTime.Now - now).TotalMilliseconds >= (double)this.PoolTimeout.Value)                        {                            break;                        }                    }                    else                    {                        redisClient = this.CreateRedisClient();                        if (redisClient != null)                        {                            goto Block_5;                        }                    }                }                else                {                    if (!redisClient.HadExceptions)                    {                        goto Block_6;                    }                    List<RedisClient> obj = this.writeClients;                    lock (obj)                    {                        this.writeClients.Remove(redisClient);                        this.redisClientSize--;                    }                    RedisState.DisposeDeactivatedClient(redisClient);                }            }            bool flag2 = true;            if (flag2)            {                throw new TimeoutException("Redis Timeout expired. The timeout period elapsed prior to obtaining a connection from the pool. This may have occurred because all pooled connections were in use.");            }            return redisClient;        Block_5:            this.writeClients.Add(redisClient);            return redisClient;        Block_6:            redisClient.Active = true;            this.InitClient(redisClient);            return redisClient;        }

此方法的主体是死循环，主要实现了这几项功能：

• this.deactiveClientQueue代表空闲的Client集合，是ConcurrentStack<RedisClient>类型的。
• 当this.deactiveClientQueue能够Pop出redisClient时，则跳转到Block_6分支：标记redisClient.Active属性，并执行this.InitClient(redisClient)，然后将redisClient实例返回。
• 当this.deactiveClientQueue没有可以Pop的元素时，首先执行Client数量上限的判断this.redisClientSize >= this.maxRedisClient；如果未到达上限，则执行redisClient = this.CreateRedisClient();如果达到上限，则先休眠3毫秒，然后判断是否超过连接池超时时间this.PoolTimeout，单位毫秒。超时的话直接break中断循环，不超时的话继续下一次for循环。

上述流程就是从连接池获取Client的主要流程，其中this.deactiveClientQueue相当于“Client池”。需要注意this.PoolTimeout的含义是当连接池耗尽时调用方等待的时间。

上述过程通过流程图表示为：

创建新Client的过程：CreateRedisClient()

源码如下：

查看代码

 private RedisClient CreateRedisClient(){if (this.redisClientSize >= this.maxRedisClient){return null;}object obj = this.lckObj;RedisClient result;lock (obj){if (this.redisClientSize >= this.maxRedisClient){result = null;}else{Random random = new Random((int)DateTime.Now.Ticks);RedisClient newClient = this.InitNewClient(this.RedisResolver.CreateMasterClient(random.Next(100)));newClient.OnDispose += delegate(){if (!newClient.HadExceptions){List<RedisClient> obj2 = this.writeClients;lock (obj2){if (!newClient.HadExceptions){try{this.deactiveClientQueue.Push(newClient);return;}catch{this.writeClients.Remove(newClient);this.redisClientSize--;RedisState.DisposeDeactivatedClient(newClient);}}}}this.writeClients.Remove(newClient);this.redisClientSize--;RedisState.DisposeDeactivatedClient(newClient);};this.redisClientSize++;result = newClient;}}return result;}

基于并发的考虑，创建新Client的流程需要增加并发锁限制，即lock (obj)处。此时如果多个线程都进入CreateRedisClient()方法，则只有一个线程实际执行，其它线程阻塞等待锁释放。这个现象可以通过windbg的syncblk、clrstack命令分析查看。其余的部分就是继续调用this.InitNewClient(
this.RedisResolver.CreateMasterClient(random.Next(100)))创建对象，并对newClient的OnDispose事件增加了处理逻辑。需要说明的是此处OnDispose事件并不是传统意义的析构，而是调用方用完此RedisClient对象后，用于将其回收到连接池的操作，即：newClient对象没有异常的前提下， 将其Push到this.deactiveClientQueue栈里，连接池就是此处回收扩充的。

this.InitNewClient()方法解读

此处是对新创建的RedisClient对象初始化，包括Id、Active等，并继续调用this.InitClient()进一步初始化。

this.RedisResolver.CreateMasterClient()解读

this.redisResolver是IRedisResolver接口类型，源码中有三种实现，如下截图。此处以生产常见的哨兵模式为例进行分析。

RedisSentinelResolver类对应的就是哨兵模式，其相关操作源码如下：

查看代码

public RedisClient CreateMasterClient(int desiredIndex){return this.CreateRedisClient(this.GetReadWriteHost(desiredIndex), true);}public RedisEndpoint GetReadWriteHost(int desiredIndex){return this.sentinel.GetMaster() ?? this.masters[desiredIndex % this.masters.Length];}public virtual RedisClient CreateRedisClient(RedisEndpoint config, bool master){RedisClient result = this.ClientFactory(config);if (master){RedisServerRole redisServerRole = RedisServerRole.Unknown;try{using (RedisClient redisClient = this.ClientFactory(config)){redisClient.ConnectTimeout = 5000;redisClient.ReceiveTimeout = 5000;redisServerRole = redisClient.GetServerRole();if (redisServerRole == RedisServerRole.Master){this.lastValidMasterFromSentinelAt = DateTime.UtcNow;return result;}}}catch (Exception exception){Interlocked.Increment(ref RedisState.TotalInvalidMasters);using (RedisClient redisClient2 = this.ClientFactory(config)){redisClient2.ConnectTimeout = 5000;redisClient2.ReceiveTimeout = 5000;if (redisClient2.GetHostString() == this.lastInvalidMasterHost){object obj = this.oLock;lock (obj){if (DateTime.UtcNow - this.lastValidMasterFromSentinelAt > this.sentinel.WaitBeforeForcingMasterFailover){this.lastInvalidMasterHost = null;this.lastValidMasterFromSentinelAt = DateTime.UtcNow;RedisSentinelResolver.log.Error("Valid master was not found at '{0}' within '{1}'. Sending SENTINEL failover...".Fmt(redisClient2.GetHostString(), this.sentinel.WaitBeforeForcingMasterFailover), exception);Interlocked.Increment(ref RedisState.TotalForcedMasterFailovers);this.sentinel.ForceMasterFailover();Thread.Sleep(this.sentinel.WaitBetweenFailedHosts);redisServerRole = redisClient2.GetServerRole();}goto IL_16E;}}this.lastInvalidMasterHost = redisClient2.GetHostString();IL_16E:;}}if (redisServerRole != RedisServerRole.Master && RedisConfig.VerifyMasterConnections){try{Stopwatch stopwatch = Stopwatch.StartNew();for (;;){try{RedisEndpoint master2 = this.sentinel.GetMaster();using (RedisClient redisClient3 = this.ClientFactory(master2)){redisClient3.ReceiveTimeout = 5000;redisClient3.ConnectTimeout = this.sentinel.SentinelWorkerConnectTimeoutMs;if (redisClient3.GetServerRole() == RedisServerRole.Master){this.lastValidMasterFromSentinelAt = DateTime.UtcNow;return this.ClientFactory(master2);}Interlocked.Increment(ref RedisState.TotalInvalidMasters);}}catch{}if (stopwatch.Elapsed > this.sentinel.MaxWaitBetweenFailedHosts){break;}Thread.Sleep(this.sentinel.WaitBetweenFailedHosts);}throw new TimeoutException("Max Wait Between Sentinel Lookups Elapsed: {0}".Fmt(this.sentinel.MaxWaitBetweenFailedHosts.ToString()));}catch (Exception exception2){RedisSentinelResolver.log.Error("Redis Master Host '{0}' is {1}. Resetting allHosts...".Fmt(config.GetHostString(), redisServerRole), exception2);List<RedisEndpoint> list = new List<RedisEndpoint>();List<RedisEndpoint> list2 = new List<RedisEndpoint>();RedisClient redisClient4 = null;foreach (RedisEndpoint redisEndpoint in this.allHosts){try{using (RedisClient redisClient5 = this.ClientFactory(redisEndpoint)){redisClient5.ReceiveTimeout = 5000;redisClient5.ConnectTimeout = RedisConfig.HostLookupTimeoutMs;RedisServerRole serverRole = redisClient5.GetServerRole();if (serverRole != RedisServerRole.Master){if (serverRole == RedisServerRole.Slave){list2.Add(redisEndpoint);}}else{list.Add(redisEndpoint);if (redisClient4 == null){redisClient4 = this.ClientFactory(redisEndpoint);}}}}catch{}}if (redisClient4 == null){Interlocked.Increment(ref RedisState.TotalNoMastersFound);string message = "No master found in: " + string.Join(", ", this.allHosts.Map((RedisEndpoint x) => x.GetHostString()));RedisSentinelResolver.log.Error(message);throw new Exception(message);}this.ResetMasters(list);this.ResetSlaves(list2);return redisClient4;}return result;}return result;}return result;}

其中GetReadWriteHost()方法的逻辑是：优先使用this.sentinel.GetMaster()得到的主节点信息。如果GetMaster()失败，则从现有的主节点集合masters中随机选择一个进行连接。

然后进入CreateRedisClient()方法内：

• 首先通过this.ClientFactory()工厂创建对象redisClient，工厂内部实现了计数和new RedisClient()操作。没有太多内容。
• 然后是执行redisClient.GetServerRole()，代表向服务器核实当前连接的节点确实是Master角色。如果确认，则直接返回给调用方。【如果发送查询请求的过程出现异常，且符合一定条件，则会发起故障转移请求，即this.sentinel.ForceMasterFailover();】
• 如果当前连接的不是Master角色的节点，则多次调用this.sentinel.GetMaster()查询Master节点信息并重新实例化RedisClient对象；
• 如果超时仍然未能连接到Master节点，则会进入catch异常处理流程，遍历this.allHosts全部节点并更新对应的节点角色。

至此，通过上述的流程，最终能够得到master节点的RedisClient对象，并返回给调用方。

上述过程中，还有几处方法的实现比较重要和复杂，下面对其一一解释说明：

RedisSentinel类的GetMaster()实现原理解析

调用处很简单，但是此方法的实现操作挺多，RedisSentinel类 源码如下：

查看代码

public RedisEndpoint GetMaster(){RedisSentinelWorker validSentinelWorker = this.GetValidSentinelWorker();RedisSentinelWorker obj = validSentinelWorker;RedisEndpoint result;lock (obj){string masterHost = validSentinelWorker.GetMasterHost(this.masterName);if (this.ScanForOtherSentinels && DateTime.UtcNow - this.lastSentinelsRefresh > this.RefreshSentinelHostsAfter){this.RefreshActiveSentinels();}result = ((masterHost != null) ? ((this.HostFilter != null) ? this.HostFilter(masterHost) : masterHost).ToRedisEndpoint(null) : null);}return result;}private RedisSentinelWorker GetValidSentinelWorker(){if (this.isDisposed){throw new ObjectDisposedException(base.GetType().Name);}if (this.worker != null){return this.worker;}RedisException innerException = null;while (this.worker == null && this.ShouldRetry()){try{this.worker = this.GetNextSentinel();this.GetSentinelInfo();this.worker.BeginListeningForConfigurationChanges();this.failures = 0;return this.worker;}catch (RedisException ex){if (this.OnWorkerError != null){this.OnWorkerError(ex);}innerException = ex;this.worker = null;this.failures++;Interlocked.Increment(ref RedisState.TotalFailedSentinelWorkers);}}this.failures = 0;Thread.Sleep(this.WaitBetweenFailedHosts);throw new RedisException("No Redis Sentinels were available", innerException);}private RedisSentinelWorker GetNextSentinel(){object obj = this.oLock;RedisSentinelWorker result;lock (obj){if (this.worker != null){this.worker.Dispose();this.worker = null;}int num = this.sentinelIndex + 1;this.sentinelIndex = num;if (num >= this.SentinelEndpoints.Length){this.sentinelIndex = 0;}result = new RedisSentinelWorker(this, this.SentinelEndpoints[this.sentinelIndex]){OnSentinelError = new Action<Exception>(this.OnSentinelError)};}return result;}private void OnSentinelError(Exception ex){if (this.worker != null){RedisSentinel.Log.Error("Error on existing SentinelWorker, reconnecting...");if (this.OnWorkerError != null){this.OnWorkerError(ex);}this.worker = this.GetNextSentinel();this.worker.BeginListeningForConfigurationChanges();}}

先通过GetValidSentinelWorker()获得RedisSentinelWorker对象。此方法的实现包含了重试机制的控制，最终是通过this.GetNextSentinel()方法给this.worker字段，即RedisSentinelWorker对象实例。

而GetNextSentinel()方法内部包含了同步锁、调用this.worker.Dispose()、随机选择哨兵节点、实例化RedisSentinelWorker对象等操作。

后面是对validSentinelWorker进行加锁，然后继续执行string masterHost =
validSentinelWorker.GetMasterHost(this.masterName);

对应的RedisSentinelWorker类的代码如下：

查看代码

internal string GetMasterHost(string masterName){string result;try{result = this.GetMasterHostInternal(masterName);}catch (Exception obj){if (this.OnSentinelError != null){this.OnSentinelError(obj);}result = null;}return result;}private string GetMasterHostInternal(string masterName){List<string> list = this.sentinelClient.SentinelGetMasterAddrByName(masterName);if (list.Count <= 0){return null;}return this.SanitizeMasterConfig(list);}public void Dispose(){new IDisposable[]{this.sentinelClient,this.sentinePubSub}.Dispose(RedisSentinelWorker.Log);}

注意GetMasterHost()方法内：当发生异常时，会触发this对象的OnSentinelError事件，顾名思义这个事件用于哨兵异常的后续处理。通过源码搜索，只有GetNextSentinel()方法内对OnSentinelError事件增加了处理程序-->即RedisSentinel内的private void OnSentinelError(Exception ex)方法。而这个方法内部对打印日志和触发事件this.OnWorkerError后，又调用GetNextSentinel()重新给this.worker字段赋值。

需要注意：Dispose()方法实际是分别调用了this.sentinelClient和this.sentinePubSub的注销操作。

RedisNativeClient类的相关功能和实现

接着调用了RedisNativeClient类的
SentinelGetMasterAddrByName()方法：

这个类里的几个方法的含义综合起来就是：将哨兵客户端的查询指令通过Socket发送到服务端，并将返回结果格式化为所需的RedisEndpoint类型。

在方法SendReceive()内还包含了Socket连接、重试、频率控制、超时控制等机制。

查看代码

public List<string> SentinelGetMasterAddrByName(string masterName){List<byte[]> list = new List<byte[]>{Commands.Sentinel,Commands.GetMasterAddrByName,masterName.ToUtf8Bytes()};return this.SendExpectMultiData(list.ToArray()).ToStringList();}protected byte[][] SendExpectMultiData(params byte[][] cmdWithBinaryArgs){return this.SendReceive<byte[][]>(cmdWithBinaryArgs, new Func<byte[][]>(this.ReadMultiData), (this.Pipeline != null) ? new Action<Func<byte[][]>>(this.Pipeline.CompleteMultiBytesQueuedCommand) : null, false) ?? TypeConstants.EmptyByteArrayArray;}protected T SendReceive<T>(byte[][] cmdWithBinaryArgs, Func<T> fn, Action<Func<T>> completePipelineFn = null, bool sendWithoutRead = false){int num = 0;Exception ex = null;DateTime utcNow = DateTime.UtcNow;T t;for (;;){try{this.TryConnectIfNeeded();if (this.socket == null){throw new RedisRetryableException("Socket is not connected");}if (num == 0){this.WriteCommandToSendBuffer(cmdWithBinaryArgs);}if (this.Pipeline == null){this.FlushSendBuffer();}else if (!sendWithoutRead){if (completePipelineFn == null){throw new NotSupportedException("Pipeline is not supported.");}completePipelineFn(fn);t = default(T);t = t;break;}T t2 = default(T);if (fn != null){t2 = fn();}if (this.Pipeline == null){this.ResetSendBuffer();}if (num > 0){Interlocked.Increment(ref RedisState.TotalRetrySuccess);}Interlocked.Increment(ref RedisState.TotalCommandsSent);t = t2;}catch (Exception ex2){RedisRetryableException ex3 = ex2 as RedisRetryableException;if ((ex3 == null && ex2 is RedisException) || ex2 is LicenseException){this.ResetSendBuffer();throw;}Exception ex4 = ex3 ?? this.GetRetryableException(ex2);if (ex4 == null){throw this.CreateConnectionError(ex ?? ex2);}if (ex == null){ex = ex4;}if (!(DateTime.UtcNow - utcNow < this.retryTimeout)){if (this.Pipeline == null){this.ResetSendBuffer();}Interlocked.Increment(ref RedisState.TotalRetryTimedout);throw this.CreateRetryTimeoutException(this.retryTimeout, ex);}Interlocked.Increment(ref RedisState.TotalRetryCount);Thread.Sleep(RedisNativeClient.GetBackOffMultiplier(++num));continue;}break;}return t;}

总结

本文着重以Redis连接创建、获取为线索，对SDK内部的实现机制有了更深入的了解。在此基础上，分析生产环境Redis SDK相关故