ServiceStack.Redis的源码分析（连接与连接池）

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，通过此文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相关故障时更加得心应手。