【Orleans开胃菜系列2】连接Connect源码简易分析

简要说明

//连接代码。
 using (var client = await StartClientWithRetries())
                {
                   
                }

从方法看，只是一个简单允许重试的启动客户端。追踪进去会发现关于重试逻辑的实践，Socket编程的实践，基于内存的消息队列的实践，依赖注入。再看源码的基础上，最好能配合一些理论书籍来看。理论指导实践，实践反馈理论，才是技术成长的步骤。

这篇文章只涉及Connect所引用方法的部分说明，一步一步来加深理解。
本来我是打算把orleans研究透之后再来写一篇，但看了一周之后，发下connect里面调用了很多类，每个类又有很多方法，这样下去没有尽头，到最终估计什么也写不成。

分析源码本来就是循环渐进的过程，也是一个熟悉框架/原理/实践的过程。直接跳过这个步骤，必然损失良多。所以这部分就叫开胃菜吧。在查看connect过程，会越来越接触到各种知识。

本篇暂不涉及数据持久化，主要依赖.netcore内置方法操纵内存实现。

您会接触到的扩展知识

扩展知识之Timer&TimerQueue
Timer

Timer
在设置的间隔后生成事件，并提供生成重复事件的选项

TimerQueue
时间队列

扩展知识之信号量
SemaphoreSlim
SemaphoreSlim 实现

//信号量
SemaphoreSlim
表示Semaphore的轻量级替代，它限制了可以同时访问资源或资源池的线程数
>>Release 释放
>> Wait 等待。

信号量有两种类型：本地信号量和命名系统信号量。前者是应用程序的本地。后者在整个操作系统中是可见的，并且适用于进程间同步。该SemaphoreSlim是一个轻量级替代信号量不使用Windows内核中的信号类。与Semaphore类不同，SemaphoreSlim类不支持命名系统信号量。您只能将其用作本地信号量。所述SemaphoreSlim类为单一的应用程序内的同步推荐的信号量。

扩展知识之BlockingCollection
BlockingCollection介绍
利用BlockingCollection实现生产者和消费者队列

BlockingCollection
为实现 IProducerConsumerCollection<T> 的线程安全集合提供阻塞和限制功能。
  >> Take
  >> Add
  有这个类型，

扩展知识之Interlocked
Interlocked

Interlocked为多个线程共享的变量提供原子操作。
>>Add
>>Decrement以原子操作的形式递减指定变量的值并存储结果。
>>Increment以原子操作的形式递增指定变量的值并存储结果
>>Exchange
>>CompareExchange 
>>Read
个人想法：和Redis的Increment/Decrement类似，部分情况下可以取代Redis的increment/decrement，提高速度。

扩展知识之SpinWait
SpinWait
两阶段提交
Monitor

SpinWait
为基于旋转的等待提供支持。
SpinWait是一种值类型，这意味着低级代码可以使用SpinWait而不必担心不必要的分配开销。SpinWait通常不适用于普通应用程序。在大多数情况下，您应该使用.NET Framework提供的同步类，例如Monitor
>> SpinOnce

扩展知识之Queue&Stack
Queue
Stack

Queue<T>
表示先进先出的对象集合,此类将通用队列实现为循环数组。存储在队列<T>中的对象在一端插入并从另一端移除。
>Enqueue
>Dequeue
>Peek

Stack<T>
表示具有相同指定类型的实例的可变大小后进先出（LIFO）集合。
>Push
>Pop
>PeeK

ConcurrentQueue <T>
表示线程安全的先进先出的对象集合
ConcurrentStack <T> 
表示线程安全的后进先出（LIFO）集合

如果需要以与存储在集合中的顺序相同的顺序访问信息，请使用Queue <T>。如果需要以相反的顺序访问信息，请使用Stack <T>。使用ConcurrentQueue <T>或ConcurrentStack <T> 如果您需要同时从多个线程访问该集合。

扩展知识之Task
TaskCompletionSource
基于Task的异步模式--全面介绍

TaskCompletionSource表示未绑定到委托的Task <TResult>的生产者端，通过Task属性提供对使用者端的访问。

扩展知识之线程安全的集合
System.Collections.Concurrent
ConcurrentDictionary
ConcurrentDictionary 对决 Dictionary+Locking

System.Collections.Concurrent提供了应在的地方对应的类型在使用几个线程安全的集合类System.Collections中和System.Collections.Generic命名空间，只要多线程并发访问的集合。
但是，通过当前集合实现的其中一个接口访问的成员（包括扩展方法）不保证是线程安全的，并且可能需要由调用者同步。

ConcurrentDictionary:表示可以由多个线程同时访问的键/值对的线程安全集合
对于ConcurrentDictionary <TKey，TValue>类上的所有其他操作，所有这些操作都是原子操作并且是线程安全的。唯一的例外是接受委托的方法，即AddOrUpdate和GetOrAdd。对于字典的修改和写入操作，ConcurrentDictionary <TKey，TValue>使用细粒度锁定来确保线程安全。（对字典的读取操作是以无锁方式执行的。）但是，这些方法的委托在锁外部调用，以避免在锁定下执行未知代码时可能出现的问题。因此，这些代理执行的代码不受操作的原子性影响。

扩展知识之网络编程
Socket微软官方文档
Socket博客园

Socket 类提供一组丰富的方法和属性进行网络通信
TCP协议
>BeginConnect
>EndConnect
>BeginSend
>EndSend
>BeginReceive
>EndReceive
>BeginAccept
>EndAccept
UDP协议
>BeginSendTo
>EndSendTo
>BeginReceiveFromandEndReceiveFrom

扩展知识之线程通知：
AutoResetEvent
ManualResetEvent
ManualResetEventSlim

AutoResetEvent允许线程通过信令相互通信。通常，当线程需要对资源的独占访问时，可以使用此类。
>Set释放线程
>WaitOne等待线程

ManualResetEvent
通知一个或多个等待线程发生了事件

ManualResetEventSlim
当等待时间预期非常短，并且事件未跨越进程边界时，您可以使用此类以获得比ManualResetEvent更好的性能

扩展知识之依赖注入：
ActivatorUtilities
扩展.net-使用.netcore进行依赖注入

服务可以通过两种机制来解析：
IServiceProvider
ActivatorUtilities – 允许在依赖关系注入容器中创建没有服务注册的对象。 ActivatorUtilities 用于面向用户的抽象，例如标记帮助器、MVC 控制器、SignalR 集线器和模型绑定器。
>ActivatorUtilities.CreateInstance
>ActivatorUtilities.GetServiceOrCreateInstance

Client连接代码。

//连接代码。
 using (var client = await StartClientWithRetries())
                {
                    await DoClientWork(client);
                    Console.ReadKey();
                }

重点分析StartClientWithRetries

• UseLocalhostClustering 用来配置连接参数：端口/ClusterId/ServiceId等。 配置一个连接本地silo的客户端，也有其他类型的如： UseServiceProviderFactory，UseStaticClustering

• ConfigureLogging配置日志参数扩展阅读

• Build用来注册默认服务和构建容器,扩展了解依赖注入知识。微软自带Microsoft.Extensions.DependencyInjection库

private static async Task<IClusterClient> StartClientWithRetries()
        {
            attempt = 0;
            IClusterClient client;
            client = new ClientBuilder()
                .UseLocalhostClustering()
                .Configure<ClusterOptions>(options =>
                {
                    options.ClusterId = "dev";
                    options.ServiceId = "HelloWorldApp";
                })
                .ConfigureLogging(logging => logging.AddConsole())
                .Build();

            await client.Connect(RetryFilter);
            Console.WriteLine("Client successfully connect to silo host");
            return client;
        }

先来看下connect

这里的LockAsync，内部用了SemaphoreSlim.Wait需要扩展了解下。和lock的区别。信号量本地信号量和系统信号量。
这里用state来维护生命周期

public async Task Connect(Func<Exception, Task<bool>> retryFilter = null)
        {
            this.ThrowIfDisposedOrAlreadyInitialized();
            using (await this.initLock.LockAsync().ConfigureAwait(false))
            {
                this.ThrowIfDisposedOrAlreadyInitialized();
                if (this.state == LifecycleState.Starting)
                {
                    throw new InvalidOperationException("A prior connection attempt failed. This instance must be disposed.");
                }
                
                this.state = LifecycleState.Starting;
                if (this.runtimeClient is OutsideRuntimeClient orc) await orc.Start(retryFilter).ConfigureAwait(false);
                await this.clusterClientLifecycle.OnStart().ConfigureAwait(false);
                this.state = LifecycleState.Started;
            }
        }

看下orc.Start

 public async Task Start(Func<Exception, Task<bool>> retryFilter = null)
        {
            // Deliberately avoid capturing the current synchronization context during startup and execute on the default scheduler.
            // This helps to avoid any issues (such as deadlocks) caused by executing with the client's synchronization context/scheduler.
            await Task.Run(() => this.StartInternal(retryFilter)).ConfigureAwait(false);

            logger.Info(ErrorCode.ProxyClient_StartDone, "{0} Started OutsideRuntimeClient with Global Client ID: {1}", BARS, CurrentActivationAddress.ToString() + ", client GUID ID: " + handshakeClientId);
        }

重要的StartInternal

gateways获取网关列表
transport用来维护客户端消息管理。
RunClientMessagePump用来处理接收分发消息。

 private async Task StartInternal(Func<Exception, Task<bool>> retryFilter)
        {
            // Initialize the gateway list provider, since information from the cluster is required to successfully
            // initialize subsequent services.
            var initializedGatewayProvider = new[] {false};
            await ExecuteWithRetries(async () =>
                {
                    if (!initializedGatewayProvider[0])
                    {
                        await this.gatewayListProvider.InitializeGatewayListProvider();
                        initializedGatewayProvider[0] = true;
                    }

                    var gateways = await this.gatewayListProvider.GetGateways();
                    if (gateways.Count == 0)
                    {
                        var gatewayProviderType = this.gatewayListProvider.GetType().GetParseableName();
                        var err = $"Could not find any gateway in {gatewayProviderType}. Orleans client cannot initialize.";
                        logger.Error(ErrorCode.GatewayManager_NoGateways, err);
                        throw new SiloUnavailableException(err);
                    }
                },
                retryFilter);

            var generation = -SiloAddress.AllocateNewGeneration(); // Client generations are negative
            transport = ActivatorUtilities.CreateInstance<ClientMessageCenter>(this.ServiceProvider, localAddress, generation, handshakeClientId);
            transport.Start();
            CurrentActivationAddress = ActivationAddress.NewActivationAddress(transport.MyAddress, handshakeClientId);

            listeningCts = new CancellationTokenSource();
            var ct = listeningCts.Token;
            listenForMessages = true;

            // Keeping this thread handling it very simple for now. Just queue task on thread pool.
            Task.Run(
                () =>
                {
                    while (listenForMessages && !ct.IsCancellationRequested)
                    {
                        try
                        {
                            RunClientMessagePump(ct);
                        }
                        catch (Exception exc)
                        {
                            logger.Error(ErrorCode.Runtime_Error_100326, "RunClientMessagePump has thrown exception", exc);
                        }
                    }
                },
                ct).Ignore();

            await ExecuteWithRetries(
                async () => this.GrainTypeResolver = await transport.GetGrainTypeResolver(this.InternalGrainFactory),
                retryFilter);

            this.typeMapRefreshTimer = new AsyncTaskSafeTimer(
                this.logger, 
                RefreshGrainTypeResolver, 
                null,
                this.typeMapRefreshInterval,
                this.typeMapRefreshInterval);

            ClientStatistics.Start(transport, clientId);
            
            await ExecuteWithRetries(StreamingInitialize, retryFilter);

            async Task ExecuteWithRetries(Func<Task> task, Func<Exception, Task<bool>> shouldRetry)
            {
                while (true)
                {
                    try
                    {
                        await task();
                        return;
                    }
                    catch (Exception exception) when (shouldRetry != null)
                    {
                        var retry = await shouldRetry(exception);
                        if (!retry) throw;
                    }
                }
            }
        }

重点关注下StartInternal里面ClientMessageCenter的初始化

用来处理消息分发等，也涉及网关部分调用。

 public ClientMessageCenter(
            IOptions<GatewayOptions> gatewayOptions,
            IOptions<ClientMessagingOptions> clientMessagingOptions,
            IPAddress localAddress,
            int gen,
            GrainId clientId,
            IGatewayListProvider gatewayListProvider,
            SerializationManager serializationManager,
            IRuntimeClient runtimeClient,
            MessageFactory messageFactory,
            IClusterConnectionStatusListener connectionStatusListener,
            ExecutorService executorService,
            ILoggerFactory loggerFactory,
            IOptions<NetworkingOptions> networkingOptions,
            IOptions<StatisticsOptions> statisticsOptions)
        {
            this.loggerFactory = loggerFactory;
            this.openConnectionTimeout = networkingOptions.Value.OpenConnectionTimeout;
            this.SerializationManager = serializationManager;
            this.executorService = executorService;
            lockable = new object();
            MyAddress = SiloAddress.New(new IPEndPoint(localAddress, 0), gen);
            ClientId = clientId;
            this.RuntimeClient = runtimeClient;
            this.messageFactory = messageFactory;
            this.connectionStatusListener = connectionStatusListener;
            Running = false;
            GatewayManager = new GatewayManager(gatewayOptions.Value, gatewayListProvider, loggerFactory);
            PendingInboundMessages = new BlockingCollection<Message>();
            gatewayConnections = new Dictionary<Uri, GatewayConnection>();
            numMessages = 0;
            grainBuckets = new WeakReference[clientMessagingOptions.Value.ClientSenderBuckets];
            logger = loggerFactory.CreateLogger<ClientMessageCenter>();
            if (logger.IsEnabled(LogLevel.Debug)) logger.Debug("Proxy grain client constructed");
            IntValueStatistic.FindOrCreate(
                StatisticNames.CLIENT_CONNECTED_GATEWAY_COUNT,
                () =>
                {
                    lock (gatewayConnections)
                    {
                        return gatewayConnections.Values.Count(conn => conn.IsLive);
                    }
                });
            statisticsLevel = statisticsOptions.Value.CollectionLevel;
            if (statisticsLevel.CollectQueueStats())
            {
                queueTracking = new QueueTrackingStatistic("ClientReceiver", statisticsOptions);
            }
        }

关注下StartInternal的RunClientMessagePump

WaitMessage里面利用了BlockingCollection.Take

 private void RunClientMessagePump(CancellationToken ct)
        {
            incomingMessagesThreadTimeTracking?.OnStartExecution();

            while (listenForMessages)
            {
                var message = transport.WaitMessage(Message.Categories.Application, ct);

                if (message == null) // if wait was cancelled
                    break;

                // when we receive the first message, we update the
                // clientId for this client because it may have been modified to
                // include the cluster name
                if (!firstMessageReceived)
                {
                    firstMessageReceived = true;
                    if (!handshakeClientId.Equals(message.TargetGrain))
                    {
                        clientId = message.TargetGrain;
                        transport.UpdateClientId(clientId);
                        CurrentActivationAddress = ActivationAddress.GetAddress(transport.MyAddress, clientId, CurrentActivationAddress.Activation);
                    }
                    else
                    {
                        clientId = handshakeClientId;
                    }
                }

                switch (message.Direction)
                {
                    case Message.Directions.Response:
                        {
                            ReceiveResponse(message);
                            break;
                        }
                    case Message.Directions.OneWay:
                    case Message.Directions.Request:
                        {
                            this.localObjects.Dispatch(message);
                            break;
                        }
                    default:
                        logger.Error(ErrorCode.Runtime_Error_100327, $"Message not supported: {message}.");
                        break;
                }
            }

            incomingMessagesThreadTimeTracking?.OnStopExecution();
        }

RunClientMessagePump里面的ReceiveResponse

这里主要是对response做一些判断处理。

public void ReceiveResponse(Message response)
        {
            if (logger.IsEnabled(LogLevel.Trace)) logger.Trace("Received {0}", response);

            // ignore duplicate requests
            if (response.Result == Message.ResponseTypes.Rejection && response.RejectionType == Message.RejectionTypes.DuplicateRequest)
                return;

            CallbackData callbackData;
            var found = callbacks.TryGetValue(response.Id, out callbackData);
            if (found)
            {
                // We need to import the RequestContext here as well.
                // Unfortunately, it is not enough, since CallContext.LogicalGetData will not flow "up" from task completion source into the resolved task.
                // RequestContextExtensions.Import(response.RequestContextData);
                callbackData.DoCallback(response);
            }
            else
            {
                logger.Warn(ErrorCode.Runtime_Error_100011, "No callback for response message: " + response);
            }
        }
        //DoCallBack
        public void DoCallback(Message response)
        {
            if (this.IsCompleted)
                return;
            var requestStatistics = this.shared.RequestStatistics;
            lock (this)
            {
                if (this.IsCompleted)
                    return;

                if (response.Result == Message.ResponseTypes.Rejection && response.RejectionType == Message.RejectionTypes.Transient)
                {
                    if (this.shared.ShouldResend(this.Message))
                    {
                        return;
                    }
                }

                this.IsCompleted = true;
                if (requestStatistics.CollectApplicationRequestsStats)
                {
                    this.stopwatch.Stop();
                }

                this.shared.Unregister(this.Message);
            }

            if (requestStatistics.CollectApplicationRequestsStats)
            {
                requestStatistics.OnAppRequestsEnd(this.stopwatch.Elapsed);
            }

            // do callback outside the CallbackData lock. Just not a good practice to hold a lock for this unrelated operation.
            this.shared.ResponseCallback(response, this.context);
        }

        //this.shared.Unregister(this.Message);

RunClientMessagePump里面的消息分发Dispatch(message)

这里面用ConcurrentDictionary<GuidId, LocalObjectData>来判断ObserverId是否存在，不存在移除。
如果存在,利用Queue的Enqueue将消息插入队列。

如果启动成功，异步调用LocalObjectMessagePumpAsync，然后利用Queue的Dequeue来取的最新消息，
然后调用SendResponseAsync来发送消息

private async Task LocalObjectMessagePumpAsync(LocalObjectData objectData)
        {
            while (true)
            {
                try
                {
                    Message message;
                    lock (objectData.Messages)
                    {
                        if (objectData.Messages.Count == 0)
                        {
                            objectData.Running = false;
                            break;
                        }

                        message = objectData.Messages.Dequeue();
                    }

                    if (ExpireMessageIfExpired(message, MessagingStatisticsGroup.Phase.Invoke))
                        continue;

                    RequestContextExtensions.Import(message.RequestContextData);
                    var request = (InvokeMethodRequest)message.GetDeserializedBody(this.serializationManager);
                    var targetOb = (IAddressable)objectData.LocalObject.Target;
                    object resultObject = null;
                    Exception caught = null;
                    try
                    {
                        // exceptions thrown within this scope are not considered to be thrown from user code
                        // and not from runtime code.
                        var resultPromise = objectData.Invoker.Invoke(targetOb, request);
                        if (resultPromise != null) // it will be null for one way messages
                        {
                            resultObject = await resultPromise;
                        }
                    }
                    catch (Exception exc)
                    {
                        // the exception needs to be reported in the log or propagated back to the caller.
                        caught = exc;
                    }

                    if (caught != null)
                        this.ReportException(message, caught);
                    else if (message.Direction != Message.Directions.OneWay)
                        this.SendResponseAsync(message, resultObject);
                }
                catch (Exception)
                {
                    // ignore, keep looping.
                }
            }
        }

SendResponseAsync经过序列化，DeepCopy，赋值各种请求参数等各种操作以后，来到最关键的部分
transport.SendMessage

第一步先获取活动的网关(silo),如没有则建立GatewayConnection
第二步启动Connection

Connect--调用socket创建连接
Start--GatewayClientReceiver间接调用Socket来接收消息，

 public void SendMessage(Message msg)
        {
            GatewayConnection gatewayConnection = null;
            bool startRequired = false;

            if (!Running)
            {
                this.logger.Error(ErrorCode.ProxyClient_MsgCtrNotRunning, $"Ignoring {msg} because the Client message center is not running");
                return;
            }

            // If there's a specific gateway specified, use it
            if (msg.TargetSilo != null && GatewayManager.GetLiveGateways().Contains(msg.TargetSilo.ToGatewayUri()))
            {
                Uri addr = msg.TargetSilo.ToGatewayUri();
                lock (lockable)
                {
                    if (!gatewayConnections.TryGetValue(addr, out gatewayConnection) || !gatewayConnection.IsLive)
                    {
                        gatewayConnection = new GatewayConnection(addr, this, this.messageFactory, executorService, this.loggerFactory, this.openConnectionTimeout);
                        gatewayConnections[addr] = gatewayConnection;
                        if (logger.IsEnabled(LogLevel.Debug)) logger.Debug("Creating gateway to {0} for pre-addressed message", addr);
                        startRequired = true;
                    }
                }
            }
            // For untargeted messages to system targets, and for unordered messages, pick a next connection in round robin fashion.
            else if (msg.TargetGrain.IsSystemTarget || msg.IsUnordered)
            {
                // Get the cached list of live gateways.
                // Pick a next gateway name in a round robin fashion.
                // See if we have a live connection to it.
                // If Yes, use it.
                // If not, create a new GatewayConnection and start it.
                // If start fails, we will mark this connection as dead and remove it from the GetCachedLiveGatewayNames.
                lock (lockable)
                {
                    int msgNumber = numMessages;
                    numMessages = unchecked(numMessages + 1);
                    IList<Uri> gatewayNames = GatewayManager.GetLiveGateways();
                    int numGateways = gatewayNames.Count;
                    if (numGateways == 0)
                    {
                        RejectMessage(msg, "No gateways available");
                        logger.Warn(ErrorCode.ProxyClient_CannotSend, "Unable to send message {0}; gateway manager state is {1}", msg, GatewayManager);
                        return;
                    }
                    Uri addr = gatewayNames[msgNumber % numGateways];
                    if (!gatewayConnections.TryGetValue(addr, out gatewayConnection) || !gatewayConnection.IsLive)
                    {
                        gatewayConnection = new GatewayConnection(addr, this, this.messageFactory, this.executorService, this.loggerFactory, this.openConnectionTimeout);
                        gatewayConnections[addr] = gatewayConnection;
                        if (logger.IsEnabled(LogLevel.Debug)) logger.Debug(ErrorCode.ProxyClient_CreatedGatewayUnordered, "Creating gateway to {0} for unordered message to grain {1}", addr, msg.TargetGrain);
                        startRequired = true;
                    }
                    // else - Fast path - we've got a live gatewayConnection to use
                }
            }
            // Otherwise, use the buckets to ensure ordering.
            else
            {
                var index = msg.TargetGrain.GetHashCode_Modulo((uint)grainBuckets.Length);
                lock (lockable)
                {
                    // Repeated from above, at the declaration of the grainBuckets array:
                    // Requests are bucketed by GrainID, so that all requests to a grain get routed through the same bucket.
                    // Each bucket holds a (possibly null) weak reference to a GatewayConnection object. That connection instance is used
                    // if the WeakReference is non-null, is alive, and points to a live gateway connection. If any of these conditions is
                    // false, then a new gateway is selected using the gateway manager, and a new connection established if necessary.
                    var weakRef = grainBuckets[index];
                    if ((weakRef != null) && weakRef.IsAlive)
                    {
                        gatewayConnection = weakRef.Target as GatewayConnection;
                    }
                    if ((gatewayConnection == null) || !gatewayConnection.IsLive)
                    {
                        var addr = GatewayManager.GetLiveGateway();
                        if (addr == null)
                        {
                            RejectMessage(msg, "No gateways available");
                            logger.Warn(ErrorCode.ProxyClient_CannotSend_NoGateway, "Unable to send message {0}; gateway manager state is {1}", msg, GatewayManager);
                            return;
                        }
                        if (logger.IsEnabled(LogLevel.Trace)) logger.Trace(ErrorCode.ProxyClient_NewBucketIndex, "Starting new bucket index {0} for ordered messages to grain {1}", index, msg.TargetGrain);
                        if (!gatewayConnections.TryGetValue(addr, out gatewayConnection) || !gatewayConnection.IsLive)
                        {
                            gatewayConnection = new GatewayConnection(addr, this, this.messageFactory, this.executorService, this.loggerFactory, this.openConnectionTimeout);
                            gatewayConnections[addr] = gatewayConnection;
                            if (logger.IsEnabled(LogLevel.Debug)) logger.Debug(ErrorCode.ProxyClient_CreatedGatewayToGrain, "Creating gateway to {0} for message to grain {1}, bucket {2}, grain id hash code {3}X", addr, msg.TargetGrain, index,
                                               msg.TargetGrain.GetHashCode().ToString("x"));
                            startRequired = true;
                        }
                        grainBuckets[index] = new WeakReference(gatewayConnection);
                    }
                }
            }

            if (startRequired)
            {
                gatewayConnection.Start();

                if (!gatewayConnection.IsLive)
                {
                    // if failed to start Gateway connection (failed to connect), try sending this msg to another Gateway.
                    RejectOrResend(msg);
                    return;
                }
            }

            try
            {
                gatewayConnection.QueueRequest(msg);
                if (logger.IsEnabled(LogLevel.Trace)) logger.Trace(ErrorCode.ProxyClient_QueueRequest, "Sending message {0} via gateway {1}", msg, gatewayConnection.Address);
            }
            catch (InvalidOperationException)
            {
                // This exception can be thrown if the gateway connection we selected was closed since we checked (i.e., we lost the race)
                // If this happens, we reject if the message is targeted to a specific silo, or try again if not
                RejectOrResend(msg);
            }
        }

 public void Connect()
        {
            if (!MsgCenter.Running)
            {
                if (Log.IsEnabled(LogLevel.Debug)) Log.Debug(ErrorCode.ProxyClient_MsgCtrNotRunning, "Ignoring connection attempt to gateway {0} because the proxy message center is not running", Address);
                return;
            }

            // Yes, we take the lock around a Sleep. The point is to ensure that no more than one thread can try this at a time.
            // There's still a minor problem as written -- if the sending thread and receiving thread both get here, the first one
            // will try to reconnect. eventually do so, and then the other will try to reconnect even though it doesn't have to...
            // Hopefully the initial "if" statement will prevent that.
            lock (Lockable)
            {
                if (!IsLive)
                {
                    if (Log.IsEnabled(LogLevel.Debug)) Log.Debug(ErrorCode.ProxyClient_DeadGateway, "Ignoring connection attempt to gateway {0} because this gateway connection is already marked as non live", Address);
                    return; // if the connection is already marked as dead, don't try to reconnect. It has been doomed.
                }

                for (var i = 0; i < ClientMessageCenter.CONNECT_RETRY_COUNT; i++)
                {
                    try
                    {
                        if (Socket != null)
                        {
                            if (Socket.Connected)
                                return;

                            MarkAsDisconnected(Socket); // clean up the socket before reconnecting.
                        }
                        if (lastConnect != new DateTime())
                        {
                            // We already tried at least once in the past to connect to this GW.
                            // If we are no longer connected to this GW and it is no longer in the list returned
                            // from the GatewayProvider, consider directly this connection dead.
                            if (!MsgCenter.GatewayManager.GetLiveGateways().Contains(Address))
                                break;

                            // Wait at least ClientMessageCenter.MINIMUM_INTERCONNECT_DELAY before reconnection tries
                            var millisecondsSinceLastAttempt = DateTime.UtcNow - lastConnect;
                            if (millisecondsSinceLastAttempt < ClientMessageCenter.MINIMUM_INTERCONNECT_DELAY)
                            {
                                var wait = ClientMessageCenter.MINIMUM_INTERCONNECT_DELAY - millisecondsSinceLastAttempt;
                                if (Log.IsEnabled(LogLevel.Debug)) Log.Debug(ErrorCode.ProxyClient_PauseBeforeRetry, "Pausing for {0} before trying to connect to gateway {1} on trial {2}", wait, Address, i);
                                Thread.Sleep(wait);
                            }
                        }
                        lastConnect = DateTime.UtcNow;
                        Socket = new Socket(Silo.Endpoint.AddressFamily, SocketType.Stream, ProtocolType.Tcp);
                        Socket.EnableFastpath();
                        SocketManager.Connect(Socket, Silo.Endpoint, this.openConnectionTimeout);
                        NetworkingStatisticsGroup.OnOpenedGatewayDuplexSocket();
                        MsgCenter.OnGatewayConnectionOpen();
                        SocketManager.WriteConnectionPreamble(Socket, MsgCenter.ClientId);  // Identifies this client
                        Log.Info(ErrorCode.ProxyClient_Connected, "Connected to gateway at address {0} on trial {1}.", Address, i);
                        return;
                    }
                    catch (Exception ex)
                    {
                        Log.Warn(ErrorCode.ProxyClient_CannotConnect, $"Unable to connect to gateway at address {Address} on trial {i} (Exception: {ex.Message})");
                        MarkAsDisconnected(Socket);
                    }
                }
                // Failed too many times -- give up
                MarkAsDead();
            }
        }

GatewayConnection的Start会调用到GatewayClientReceiver的Run方法,利用BlockingCollection的Add方法添加到PendingInboundMessages，而之前的RunClientMessagePump里面transport.WaitMessage方法正式通过PendingInboundMessages.Take()来获取消息，至此形成了闭环。

 protected override void Run()
        {
            try
            {
                while (!Cts.IsCancellationRequested)
                {
                    int bytesRead = FillBuffer(buffer.BuildReceiveBuffer());
                    if (bytesRead == 0)
                    {
                        continue;
                    }

                    buffer.UpdateReceivedData(bytesRead);

                    Message msg;
                    while (buffer.TryDecodeMessage(out msg))
                    {
                        gatewayConnection.MsgCenter.QueueIncomingMessage(msg);
                        if (Log.IsEnabled(LogLevel.Trace)) Log.Trace("Received a message from gateway {0}: {1}", gatewayConnection.Address, msg);
                    }
                }
            }
            catch (Exception ex)
            {
                buffer.Reset();
                Log.Warn(ErrorCode.ProxyClientUnhandledExceptionWhileReceiving, $"Unexpected/unhandled exception while receiving: {ex}. Restarting gateway receiver for {gatewayConnection.Address}.", ex);
                throw;
            }
        }

关注SafeTimerBase类

Orleans用于处理定时或延时回调作业。

总结

创建一个简单的connect,里面有这么多沟沟渠渠，但本质上来说，最底层是利用Socket套接字机制来实施机制。在Socket的基础之上，又封装维护了一层GatewayConnection和GatewayClientReceiver来实现网关(Silo)的操作，比如重试/监控/熔断等，再结合Timer,Queue,BlockingCollection,Task,ConcurrentDictionary,Interlocked等知识，构建一个可用的通信框架。
说来容易几句话，实现起来都是泪。

如果您完全熟悉异步编程，并行编程，Socket网络编程。又对分布式/微服务理论有较深的理解，那么orleans实现机制，对您来说可能是相对容易。

本期结束，下期更精彩！