Asp.Net 详解IIS内部运行原理

本章节主要讲IIS和Asp.Net 管道内部如何处理客户端Http请求，会较多的以代码的形式讲述，让大家对HttpApplication、HttpHandler、HttpApplicationFactory、Page这几个在处理请求过程中扮演重要角色的对象有更深入的了解。

我们都知道，当用户在浏览器地址栏中输入网址时，该请求会被IIS服务器捕获，如果是请求的是静态页面则由IIS本身处理并直接返回客户端，如果是动态页（*.aspx），通过一序列的前期(这部分处理过程本文不详细讲解，可以参考其他文章)的处理来到.NET运行时，然后交给Aspnet_ispai.dll处理，处理完成后返回处理结果。请求和处理过程可以分为：HttpRuntime->HttpModule->HtppApplicationFactory->HttpApplication->HttpHandlerFactory->HttpHandler->HttpModule->将请求结果返回到客户端。

下面我们通过单步调式跟踪System.Web.Dll源码来分析各个过程中关键处理函数(关于如何单步调式.Net FrameWork 源码我将在后面的文章中给出)

（说明：部分代码只保留了关键代码）

1、首先进入管道运行时中的托管入口函数

IIS集成模式：

在IPipelineRuntime.cs类中请求通知函数：ProcessRequestNotification，并调用ProcessRequestNotificationHelper函数

 internal static int ProcessRequestNotification(                IntPtr rootedObjectsPointer,                IntPtr nativeRequestContext,                IntPtr moduleData,                int flags)        {            try {                //调用ProcessRequestNotificationHelper                return ProcessRequestNotificationHelper(rootedObjectsPointer, nativeRequestContext, moduleData, flags);            }            catch(Exception e) {                ApplicationManager.RecordFatalException(e);                throw;            }        }

2、在ProcessRequestNotificationHelper函数中调用运行时HttpRuntime中的ProcessRequestNotification函数

internal static int ProcessRequestNotificationHelper(                IntPtr rootedObjectsPointer,                IntPtr nativeRequestContext,                IntPtr moduleData,                int flags)        {            IIS7WorkerRequest wr = null;            HttpContext context = null;            RequestNotificationStatus status = RequestNotificationStatus.Continue;            RootedObjects root;            bool workerRequestWasJustCreated = false;                        try {                              status = HttpRuntime.ProcessRequestNotification(wr, context);//调用ProcessRequestNotification函数                }                finally {                                   }                               return (int)status;                    }

3、在ProcessRequestNotification中调用ProcessRequestNotificationPrivate

4、处理请求通知ProcessRequestNotificationPrivate函数中调用了HttpApplicatioinFactory的GetApplicationInstance()函数来获取HttpApplication实例对象，并调用BeginProcessRequestNotification处理请求

private RequestNotificationStatus ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) {            RequestNotificationStatus status = RequestNotificationStatus.Pending;            try {                                IHttpHandler handler = null;                if (context.NeedToInitializeApp()) {                    try {                        EnsureFirstRequestInit(context);                    }                    catch {                                          }                    context.Response.InitResponseWriter();                    handler = HttpApplicationFactory.GetApplicationInstance(context);//获取HttpApplication实例                    if (handler == null)                        throw new HttpException(SR.GetString(SR.Unable_create_app_object));                    if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Infrastructure)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_START_HANDLER, context.WorkerRequest, handler.GetType().FullName, "Start");                    HttpApplication app = handler as HttpApplication;                    if (app != null) {                        // associate the context with an application instance                        app.AssignContext(context);                    }                }                                wr.SynchronizeVariables(context);                if (context.ApplicationInstance != null) {                    // 处理请求                    IAsyncResult ar = context.ApplicationInstance.BeginProcessRequestNotification(context, _requestNotificationCompletionCallback);                    if (ar.CompletedSynchronously) {                        status = RequestNotificationStatus.Continue;                    }                }                else if (handler != null) {                    // HttpDebugHandler is processed here                    handler.ProcessRequest(context);                    status = RequestNotificationStatus.FinishRequest;                }                else {                    status = RequestNotificationStatus.Continue;                }            }            catch (Exception e) {                           }                    return status;        }

IIS经典模式：

在ISAPIRuntime.cs类中请求 ProcessRequest函数并调用HttpRuntime.ProcessReques方法

1、HttpRuntime处理请求入口函数

 public static void ProcessRequest(HttpWorkerRequest wr) {            if (wr == null)                throw new ArgumentNullException("wr");            if (HttpRuntime.UseIntegratedPipeline) {                throw new PlatformNotSupportedException(SR.GetString(SR.Method_Not_Supported_By_Iis_Integrated_Mode, "HttpRuntime.ProcessRequest"));            }           ProcessRequestNoDemand(wr);//调用ProcessRequestNoDemand函数        }

2、ProcessRequestNoDemand函数，调用ProcessRequestNow函数

internal static void ProcessRequestNoDemand(HttpWorkerRequest wr) {            RequestQueue rq = _theRuntime._requestQueue;            wr.UpdateInitialCounters();            if (rq != null)  // could be null before first request                wr = rq.GetRequestToExecute(wr);            if (wr != null) {                CalculateWaitTimeAndUpdatePerfCounter(wr);                wr.ResetStartTime();                ProcessRequestNow(wr);调用ProcessRequestNow            }        }

3、ProcessRequestNow函数，调用ProcessRequestInternal

internal static void ProcessRequestNow(HttpWorkerRequest wr){    _theRuntime.ProcessRequestInternal(wr);//调用ProcessRequestInternal}

4、ProcessRequestInternal函数，调用HttpApplicatioinFactory的GetApplicationInstance()函数来获取HttpApplication实例对象

private void ProcessRequestInternal(HttpWorkerRequest wr) {            // Count active requests            Interlocked.Increment(ref _activeRequestCount);                // Get application instance               IHttpHandler app = HttpApplicationFactory.GetApplicationInstance(context);//获取HttpApplication对象                if (app == null)                    throw new HttpException(SR.GetString(SR.Unable_create_app_object));                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Infrastructure)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_START_HANDLER, context.WorkerRequest, app.GetType().FullName, "Start");                if (app is IHttpAsyncHandler) {                    // asynchronous handler                    IHttpAsyncHandler asyncHandler = (IHttpAsyncHandler)app;                    context.AsyncAppHandler = asyncHandler;                   //来到了真正处理请求步骤                    asyncHandler.BeginProcessRequest(context, _handlerCompletionCallback, context);                }                else {                    // synchronous handler                    app.ProcessRequest(context);                    FinishRequest(context.WorkerRequest, context, null);                }            }            catch (Exception e) {                context.Response.InitResponseWriter();                FinishRequest(wr, context, e);            }        }

说明：以上4个步骤集成模式和经典模式分不同的函数执行，从下面开始两种模式调用相同的函数，只是在函数中针对不同的模式进行不同的处理

5、进入HttpApplicationFactory，调用GetNormalApplicationInstance函数

internal static IHttpHandler GetApplicationInstance(HttpContext context) {            if (_customApplication != null)                return _customApplication;            if (context.Request.IsDebuggingRequest)                return new HttpDebugHandler();            _theApplicationFactory.EnsureInited();            _theApplicationFactory.EnsureAppStartCalled(context);            return _theApplicationFactory.GetNormalApplicationInstance(context);//返回HttpApplication实例        }

6、进入GetNormalApplicationInstance函数，调用InitInternal初始化HttpApplication内部对象

 private HttpApplication GetNormalApplicationInstance(HttpContext context) {            HttpApplication app = null;            lock (_freeList) {                if (_numFreeAppInstances > 0) {                    app = (HttpApplication)_freeList.Pop();                    _numFreeAppInstances--;                    if (_numFreeAppInstances < _minFreeAppInstances) {                        _minFreeAppInstances = _numFreeAppInstances;                    }                }            }            if (app == null) {                // If ran out of instances, create a new one                app = (HttpApplication)HttpRuntime.CreateNonPublicInstance(_theApplicationType);                using (new ApplicationImpersonationContext()) {                    app.InitInternal(context, _state, _eventHandlerMethods);//初始化Application内部对象                }            }            if (AppSettings.UseTaskFriendlySynchronizationContext) {                // When this HttpApplication instance is no longer in use, recycle it.                app.ApplicationInstanceConsumersCounter = new CountdownTask(1); // representing required call to HttpApplication.ReleaseAppInstance                app.ApplicationInstanceConsumersCounter.Task.ContinueWith((_, o) => RecycleApplicationInstance((HttpApplication)o), app, TaskContinuationOptions.ExecuteSynchronously);            }            return app;        }

7、进入HttpApplication,调用InitInternal函数来初始化Application内部对象。初始化HttpModule和建立处理执行步骤

 internal void InitInternal(HttpContext context, HttpApplicationState state, MethodInfo[] handlers) {            Debug.Assert(context != null, "context != null");            // Remember state            _state = state;            PerfCounters.IncrementCounter(AppPerfCounter.PIPELINES);            try {                try {                    // Remember context for config lookups                    _initContext = context;                    _initContext.ApplicationInstance = this;                    // Set config path to be application path for the application initialization                    context.ConfigurationPath = context.Request.ApplicationPathObject;                    // keep HttpContext.Current working while running user code                    using (new DisposableHttpContextWrapper(context)) {                        // Build module list from config 根据IIS集成模式和经典模式初始化HttpMudule                        if (HttpRuntime.UseIntegratedPipeline) { //集成模式                            Debug.Assert(_moduleConfigInfo != null, "_moduleConfigInfo != null");                            Debug.Assert(_moduleConfigInfo.Count >= 0, "_moduleConfigInfo.Count >= 0");                            try {                                context.HideRequestResponse = true;                                _hideRequestResponse = true;                                InitIntegratedModules();//集成模式初始化HttpModule                            }                            finally {                                context.HideRequestResponse = false;                                _hideRequestResponse = false;                            }                        }                        else { //经典模式                            InitModules();//经典模式初始化HttpModule                            // this is used exclusively for integrated mode                            Debug.Assert(null == _moduleContainers, "null == _moduleContainers");                        }                        // Hookup event handlers via reflection                        if (handlers != null)                            HookupEventHandlersForApplicationAndModules(handlers);                        // Initialization of the derived class                        _context = context;                        if (HttpRuntime.UseIntegratedPipeline && _context != null) {                            _context.HideRequestResponse = true;                        }                        _hideRequestResponse = true;                        try {                            Init();                        }                        catch (Exception e) {                            RecordError(e);                        }                    }                    if (HttpRuntime.UseIntegratedPipeline && _context != null) {                        _context.HideRequestResponse = false;                    }                    _hideRequestResponse = false;                    _context = null;                    _resumeStepsWaitCallback= new WaitCallback(this.ResumeStepsWaitCallback);                    // Construct the execution steps array                    <span style="color:#FF0000;"><strong>if (HttpRuntime.UseIntegratedPipeline) {</strong></span> //集成模式 调用PipelineStepManager                        <span style="color:#FF0000;"><strong>_stepManager = new PipelineStepManager(this);</strong></span>                    }                    else {                       <span style="color:#FF0000;"><strong> _stepManager = new ApplicationStepManager(this);</strong></span> //经典模式 调用 ApplicationStepManager                    }                    <span style="color:#FF0000;"><strong>_stepManager.BuildSteps(_resumeStepsWaitCallback);</strong></span> //建立执行处理步骤                }                finally {                    _initInternalCompleted = true;                    // Reset config path                    context.ConfigurationPath = null;                    // don't hold on to the context                    _initContext.ApplicationInstance = null;                    _initContext = null;                }            }            catch { // Protect against exception filters                throw;            }        }

8、初始化HttpModule，包含系统默认的HttpModule和自定义的HttpModule

1）、系统默认的HttpModule：

C:\Windows\Microsoft.NET\Framework64\v4.0.30319\Config\web.config

2）、自定义的HttpModule在网站的Web.config中配置

经典模式：

<system.web>    <httpModules>      <add name="mymodule" type="WebApplication2.myModule"/>    </httpModules> </system.web>

集成模式：

<system.webServer>    <modules>      <add name="mymodule" type="WebApplication2.myModule"/>    </modules>  </system.webServer>

3）、经典模式初始化：

private void InitModules() {            //读取配置文件中HttpModules节点            HttpModulesSection pconfig = RuntimeConfig.GetAppConfig().HttpModules;            //获取HttpModule集合           HttpModuleCollection moduleCollection = pconfig.CreateModules();           HttpModuleCollection dynamicModules = CreateDynamicModules();            moduleCollection.AppendCollection(dynamicModules);            _moduleCollection = moduleCollection; // don't assign until all ops have succeeded            InitModulesCommon();//调用InitModulesCommon        }

4）、初始化各个HttpModule对象.

private void InitModulesCommon() {            int n = _moduleCollection.Count;            for (int i = 0; i < n; i++) {                // remember the module being inited for event subscriptions                // we'll later use this for routing                _currentModuleCollectionKey = _moduleCollection.GetKey(i);              _moduleCollection[i].Init(this);//初始化每个HttpModule            }            _currentModuleCollectionKey = null;            InitAppLevelCulture();        }

5）、初始化HttpModule，在Init函数中注册HttpApplication对象的事件，这里举了两个例子

OutputCacheModule.cs  web.config中默认第一个HttpModule

void IHttpModule.Init(HttpApplication app) {            OutputCacheSection cacheConfig = RuntimeConfig.GetAppConfig().OutputCache;            if (cacheConfig.EnableOutputCache) {                app.ResolveRequestCache += new EventHandler(this.OnEnter);                app.UpdateRequestCache += new EventHandler(this.OnLeave);            }        }

SessionStateModule.cs web.config中默认第二个HttpModule，实现Session的系统HttpModule

 public void Init(HttpApplication app) {            bool initModuleCalled = false;            SessionStateSection config = RuntimeConfig.GetAppConfig().SessionState;            if (!s_oneTimeInit) {                s_lock.AcquireWriterLock();                try {                    if (!s_oneTimeInit) {                        InitModuleFromConfig(app, config);                        initModuleCalled = true;                        if (!CheckTrustLevel(config))                            s_trustLevelInsufficient = true;                        s_timeout = (int)config.Timeout.TotalMinutes;                        s_useHostingIdentity = config.UseHostingIdentity;                        // See if we can try InProc optimization. See inline doc of s_allowInProcOptimization                        // for details.                        if (config.Mode == SessionStateMode.InProc &&                            _usingAspnetSessionIdManager) {                            s_allowInProcOptimization = true;                        }                        if (config.Mode != SessionStateMode.Custom &&                            config.Mode != SessionStateMode.Off &&                            !config.RegenerateExpiredSessionId) {                            s_allowDelayedStateStoreItemCreation = true;                        }                        s_configExecutionTimeout = RuntimeConfig.GetConfig().HttpRuntime.ExecutionTimeout;                        s_configRegenerateExpiredSessionId = config.RegenerateExpiredSessionId;                        s_configCookieless = config.Cookieless;                        s_configMode = config.Mode;                        // The last thing to set in this if-block.                        s_oneTimeInit = true;                        Debug.Trace("SessionStateModuleInit",                                    "Configuration: _mode=" + config.Mode +                                    ";Timeout=" + config.Timeout +                                    ";CookieMode=" + config.Cookieless +                                    ";SqlConnectionString=" + config.SqlConnectionString +                                    ";StateConnectionString=" + config.StateConnectionString +                                    ";s_allowInProcOptimization=" + s_allowInProcOptimization +                                    ";s_allowDelayedStateStoreItemCreation=" + s_allowDelayedStateStoreItemCreation);                    }                }                finally {                    s_lock.ReleaseWriterLock();                }            }            if (!initModuleCalled) {                InitModuleFromConfig(app, config);            }            if (s_trustLevelInsufficient) {                throw new HttpException(SR.GetString(SR.Session_state_need_higher_trust));            }        }

集成模式初始化HttpModule代码我就不贴出来了，大家可以在源码中查看

9、建立处理步骤BuildSteps，将所有要执行的步骤载入到一个IExecutionStep[]集合中，待后面ResumeSteps调用

经典模式：调用ApplicationStepManager类中的BuildSteps函数

internal class ApplicationStepManager : StepManager {            private IExecutionStep[] _execSteps;            private WaitCallback _resumeStepsWaitCallback;            private int _currentStepIndex;            private int _numStepCalls;            private int _numSyncStepCalls;            private int _endRequestStepIndex;            internal ApplicationStepManager(HttpApplication app): base(app) {            }           internal override void BuildSteps(WaitCallback stepCallback )            {                ArrayList steps = new ArrayList();                HttpApplication app = _application;                bool urlMappingsEnabled = false;                UrlMappingsSection urlMappings = RuntimeConfig.GetConfig().UrlMappings;                urlMappingsEnabled = urlMappings.IsEnabled && ( urlMappings.UrlMappings.Count > 0 );                steps.Add(new ValidateRequestExecutionStep(app));                steps.Add(new ValidatePathExecutionStep(app));                if (urlMappingsEnabled)                    steps.Add(new UrlMappingsExecutionStep(app)); // url mappings                app.CreateEventExecutionSteps(HttpApplication.EventBeginRequest, steps);                app.CreateEventExecutionSteps(HttpApplication.EventAuthenticateRequest, steps);                app.CreateEventExecutionSteps(HttpApplication.EventDefaultAuthentication, steps);                app.CreateEventExecutionSteps(HttpApplication.EventPostAuthenticateRequest, steps);                app.CreateEventExecutionSteps(HttpApplication.EventAuthorizeRequest, steps);                app.CreateEventExecutionSteps(HttpApplication.EventPostAuthorizeRequest, steps);                app.CreateEventExecutionSteps(HttpApplication.EventResolveRequestCache, steps);                app.CreateEventExecutionSteps(HttpApplication.EventPostResolveRequestCache, steps);                steps.Add(new MapHandlerExecutionStep(app));//分配一个Handler                app.CreateEventExecutionSteps(HttpApplication.EventPostMapRequestHandler, steps);                app.CreateEventExecutionSteps(HttpApplication.EventAcquireRequestState, steps);                app.CreateEventExecutionSteps(HttpApplication.EventPostAcquireRequestState, steps);                app.CreateEventExecutionSteps(HttpApplication.EventPreRequestHandlerExecute, steps);                steps.Add(app.CreateImplicitAsyncPreloadExecutionStep()); // implict async preload step                steps.Add(new CallHandlerExecutionStep(app));  // 执行HttpHandler                app.CreateEventExecutionSteps(HttpApplication.EventPostRequestHandlerExecute, steps);                app.CreateEventExecutionSteps(HttpApplication.EventReleaseRequestState, steps);                app.CreateEventExecutionSteps(HttpApplication.EventPostReleaseRequestState, steps);                steps.Add(new CallFilterExecutionStep(app));  // filtering                app.CreateEventExecutionSteps(HttpApplication.EventUpdateRequestCache, steps);                app.CreateEventExecutionSteps(HttpApplication.EventPostUpdateRequestCache, steps);                _endRequestStepIndex = steps.Count;                app.CreateEventExecutionSteps(HttpApplication.EventEndRequest, steps);                steps.Add(new NoopExecutionStep()); // the last is always there                _execSteps = new IExecutionStep[steps.Count];                steps.CopyTo(_execSteps);                // callback for async completion when reposting to threadpool thread                _resumeStepsWaitCallback = stepCallback;            }

集成模式：调用PipelineStepManager类中的 BuildSteps函数

internal override void BuildSteps(WaitCallback stepCallback) {                Debug.Trace("PipelineRuntime", "BuildSteps");                //ArrayList steps = new ArrayList();                HttpApplication app = _application;                // add special steps that don't currently                // correspond to a configured handler                IExecutionStep materializeStep = new MaterializeHandlerExecutionStep(app);                // implicit map step                app.AddEventMapping(                    HttpApplication.IMPLICIT_HANDLER,                    RequestNotification.MapRequestHandler,                    false, materializeStep);                // implicit async preload step                app.AddEventMapping(                    HttpApplication.IMPLICIT_HANDLER,                    RequestNotification.ExecuteRequestHandler,                    false, app.CreateImplicitAsyncPreloadExecutionStep());                // implicit handler routing step                IExecutionStep handlerStep = new CallHandlerExecutionStep(app);                app.AddEventMapping(                    HttpApplication.IMPLICIT_HANDLER,                    RequestNotification.ExecuteRequestHandler,                    false, handlerStep);                // implicit handler WebSockets step                IExecutionStep webSocketsStep = new TransitionToWebSocketsExecutionStep(app);                app.AddEventMapping(                    HttpApplication.IMPLICIT_HANDLER,                    RequestNotification.EndRequest,                    true /* isPostNotification */, webSocketsStep);                // add implicit request filtering step                IExecutionStep filterStep = new CallFilterExecutionStep(app);                // normally, this executes during UpdateRequestCache as a high priority module                app.AddEventMapping(                    HttpApplication.IMPLICIT_FILTER_MODULE,                    RequestNotification.UpdateRequestCache,                    false, filterStep);                // for error conditions, this executes during LogRequest as a high priority module                app.AddEventMapping(                    HttpApplication.IMPLICIT_FILTER_MODULE,                    RequestNotification.LogRequest,                    false, filterStep);                _resumeStepsWaitCallback = stepCallback;            }

10、真正处理请求阶段， 调用ResumeSteps函数来执行处理步骤

经典模式：

返回到ProcessRequestInternal函数中执行BeginProcessRequest函数

IAsyncResult IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) {            HttpAsyncResult result;            // Setup the asynchronous stuff and application variables            _context = context;            _context.ApplicationInstance = this;            _stepManager.InitRequest();            // Make sure the context stays rooted (including all async operations)            _context.Root();            // Create the async result            result = new HttpAsyncResult(cb, extraData);            // Remember the async result for use in async completions            AsyncResult = result;            if (_context.TraceIsEnabled)                HttpRuntime.Profile.StartRequest(_context);            // Start the application            ResumeSteps(null);//执行处理步骤            // Return the async result            return result;        }

ResumeSteps函数，调用ExecuteStepl函数来执行处理步骤

internal override void ResumeSteps(Exception error) {                bool appCompleted = false;                bool stepCompletedSynchronously = true;                HttpApplication app = _application;                CountdownTask appInstanceConsumersCounter = app.ApplicationInstanceConsumersCounter;                HttpContext context = app.Context;                ThreadContext threadContext = null;                AspNetSynchronizationContextBase syncContext = context.SyncContext;                Debug.Trace("Async", "HttpApplication.ResumeSteps");                try {                    if (appInstanceConsumersCounter != null) {                        appInstanceConsumersCounter.MarkOperationPending(); // ResumeSteps call started                    }                    using (syncContext.AcquireThreadLock()) {                                           //执行步骤                   error = app.ExecuteStep(_execSteps[_currentStepIndex], ref stepCompletedSynchronously);                                           }        }

集成模式：

返回到ProcessRequestNotificationPrivate函数，执行BeginProcessRequestNotification

BeginProcessRequestNotification函数，调用ResumeSteps执行处理步骤

internal IAsyncResult BeginProcessRequestNotification(HttpContext context, AsyncCallback cb){    if (this._context == null)    {        this.AssignContext(context);    }    context.CurrentModuleEventIndex = -1;    HttpAsyncResult result = new HttpAsyncResult(cb, context);    context.NotificationContext.AsyncResult = result;    this.ResumeSteps(null);//开始执行处理步骤    return result;}

 ResumeSteps

// PipelineStepManager::ResumeSteps            // called from IIS7 (on IIS thread) via BeginProcessRequestNotification            // or from an async completion (on CLR thread) via HttpApplication::ResumeStepsFromThreadPoolThread            // This attribute prevents undesirable 'just-my-code' debugging behavior (VSWhidbey 404406/VSWhidbey 609188)            [System.Diagnostics.DebuggerStepperBoundaryAttribute]            internal override void ResumeSteps(Exception error) {                HttpContext context = _application.Context;                IIS7WorkerRequest wr = context.WorkerRequest as IIS7WorkerRequest;                AspNetSynchronizationContextBase syncContext = context.SyncContext;                RequestNotificationStatus status = RequestNotificationStatus.Continue;                ThreadContext threadContext = null;                bool needToDisassociateThreadContext = false;                bool isSynchronousCompletion = false;                bool needToComplete = false;                bool stepCompletedSynchronously = false;                int currentModuleLastEventIndex = _application.CurrentModuleContainer.GetEventCount(context.CurrentNotification, context.IsPostNotification) - 1;                CountdownTask appInstanceConsumersCounter = _application.ApplicationInstanceConsumersCounter;                using (context.RootedObjects.WithinTraceBlock()) {                                     error = _application.ExecuteStep(step, ref stepCompletedSynchronously);//执行处理步骤                                        }            }

11、ExecuteStep执行BuildSteps中的各个步骤

internal Exception ExecuteStep(IExecutionStep step, ref bool completedSynchronously) {            Exception error = null;            try {                try {                    if (step.IsCancellable) {                        _context.BeginCancellablePeriod();  // request can be cancelled from this point                        try {                            step.Execute();                        }                        finally {                            _context.EndCancellablePeriod();  // request can be cancelled until this point                        }                        _context.WaitForExceptionIfCancelled();  // wait outside of finally                    }                    else {                        step.Execute();</strong></span>                    }                    if (!step.CompletedSynchronously) {                        completedSynchronously = false;                        return null;                    }                }                                   }

这里贴出了两个很重要的步骤：获取HttpHandler（MaterializeHandlerExecutionStep）和执行HttpHandler（CallHandlerExecutionStep）

经典模式：

MapHandlerExecutionStep

// execution step -- map HTTP handler (used to be a separate module)        internal class <span style="color:#FF0000;"><strong>MapHandlerExecutionStep </strong></span>: IExecutionStep {            private HttpApplication _application;            internal MapHandlerExecutionStep(HttpApplication app) {                _application = app;            }            void IExecutionStep.Execute() {                HttpContext context = _application.Context;                HttpRequest request = context.Request;                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Infrastructure)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_MAPHANDLER_ENTER, context.WorkerRequest);                //获取HttpHandler                context.Handler = _application.MapHttpHandler(                    context,                    request.RequestType,                    request.FilePathObject,                    request.PhysicalPathInternal,                    false /*useAppConfig*/);</strong></span>                Debug.Assert(context.ConfigurationPath == context.Request.FilePathObject, "context.ConfigurationPath (" +                             context.ConfigurationPath + ") != context.Request.FilePath (" + context.Request.FilePath + ")");                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Infrastructure)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_MAPHANDLER_LEAVE, context.WorkerRequest);            }            bool IExecutionStep.CompletedSynchronously {                get { return true;}            }            bool IExecutionStep.IsCancellable {                get { return false; }            }        }

MapHttpHandler获取处理请求的HttpHandler

internal IHttpHandler MapHttpHandler(HttpContext context, string requestType, VirtualPath path, string pathTranslated, bool useAppConfig){    IHttpHandler handler = (context.ServerExecuteDepth == 0) ? context.RemapHandlerInstance : null;    using (new ApplicationImpersonationContext())    {        if (handler != null)        {            return handler;        }        HttpHandlerAction mapping = this.GetHandlerMapping(context, requestType, path, useAppConfig);        if (mapping == null)        {            PerfCounters.IncrementCounter(AppPerfCounter.REQUESTS_NOT_FOUND);            PerfCounters.IncrementCounter(AppPerfCounter.REQUESTS_FAILED);            throw new HttpException(SR.GetString("Http_handler_not_found_for_request_type", new object[] { requestType }));        }        IHttpHandlerFactory factory = this.GetFactory(mapping);//获取HttpHandlerFactory对象，如果网站Web.config中自定义了HttpHandlerFactory对象，则会覆盖系统默认的        try        {            IHttpHandlerFactory2 factory2 = factory as IHttpHandlerFactory2;            if (factory2 != null)            {                handler = factory2.GetHandler(context, requestType, path, pathTranslated);//获取HttpHandler对象，如果为自定义的HttpHandlerFactory，则返回自定义HttpHandlerFactory中设置的HttpHandler            }            else            {                handler = factory.GetHandler(context, requestType, path.VirtualPathString, pathTranslated);            }        }        catch (FileNotFoundException exception)        {            if (HttpRuntime.HasPathDiscoveryPermission(pathTranslated))            {                throw new HttpException(0x194, null, exception);            }            throw new HttpException(0x194, null);        }        catch (DirectoryNotFoundException exception2)        {            if (HttpRuntime.HasPathDiscoveryPermission(pathTranslated))            {                throw new HttpException(0x194, null, exception2);            }            throw new HttpException(0x194, null);        }        catch (PathTooLongException exception3)        {            if (HttpRuntime.HasPathDiscoveryPermission(pathTranslated))            {                throw new HttpException(0x19e, null, exception3);            }            throw new HttpException(0x19e, null);        }        if (this._handlerRecycleList == null)        {            this._handlerRecycleList = new ArrayList();        }        this._handlerRecycleList.Add(new HandlerWithFactory(handler, factory));    }    return handler;}

集成模式：

MaterializeHandlerExecutionStep步骤

        internal class MaterializeHandlerExecutionStep: IExecutionStep {            private HttpApplication _application;            internal MaterializeHandlerExecutionStep(HttpApplication app) {                _application = app;            }            void IExecutionStep.Execute() {                HttpContext context = _application.Context;                HttpRequest request = context.Request;                IHttpHandler handler = null;                string configType = null;                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Infrastructure)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_MAPHANDLER_ENTER, context.WorkerRequest);                IIS7WorkerRequest wr = context.WorkerRequest as IIS7WorkerRequest;                // Get handler                if (context.RemapHandlerInstance != null){                    //RemapHandler overrides all                    wr.SetScriptMapForRemapHandler();                    context.Handler = context.RemapHandlerInstance;                }                else if (request.RewrittenUrl != null) {                    // RewritePath, we need to re-map the handler                    bool handlerExists;                    configType = wr.ReMapHandlerAndGetHandlerTypeString(context, request.Path, out handlerExists);                    if (!handlerExists) {                        // WOS 1973590: When RewritePath is used with missing handler in Integrated Mode,an empty response 200 is returned instead of 404                        throw new HttpException(404, SR.GetString(SR.Http_handler_not_found_for_request_type, request.RequestType));                    }                }                else {                    configType = wr.GetManagedHandlerType();                }                if (!String.IsNullOrEmpty(configType)) {                   IHttpHandlerFactory factory = _application.GetFactory(configType);//获取HttpHandlerFactory对象                    string pathTranslated = request.PhysicalPathInternal;                    try {                        handler = factory.GetHandler(context, request.RequestType, request.FilePath, pathTranslated);//获取HttpHandler对象                    }                    catch (FileNotFoundException e) {                        if (HttpRuntime.HasPathDiscoveryPermission(pathTranslated))                            throw new HttpException(404, null, e);                        else                            throw new HttpException(404, null);                    }                    catch (DirectoryNotFoundException e) {                        if (HttpRuntime.HasPathDiscoveryPermission(pathTranslated))                            throw new HttpException(404, null, e);                        else                            throw new HttpException(404, null);                    }                    catch (PathTooLongException e) {                        if (HttpRuntime.HasPathDiscoveryPermission(pathTranslated))                            throw new HttpException(414, null, e);                        else                            throw new HttpException(414, null);                    }                    context.Handler = handler;                    // Remember for recycling                    if (_application._handlerRecycleList == null)                        _application._handlerRecycleList = new ArrayList();                    _application._handlerRecycleList.Add(new HandlerWithFactory(handler, factory));                }                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Infrastructure)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_MAPHANDLER_LEAVE, context.WorkerRequest);            }            bool IExecutionStep.CompletedSynchronously {                get { return true;}            }            bool IExecutionStep.IsCancellable {                get { return false; }            }        }

12、执行callhandlerexecutestep步骤，调用handler.ProcessRequest(context)，如果HttpHandler类型为Page，则开始Page页生命周期

        internal class CallHandlerExecutionStep: IExecutionStep {            private HttpApplication   _application;            private AsyncCallback     _completionCallback;            private IHttpAsyncHandler _handler;       // per call            private AsyncStepCompletionInfo _asyncStepCompletionInfo; // per call            private bool              _sync;          // per call            internal CallHandlerExecutionStep(HttpApplication app) {                _application = app;                _completionCallback = new AsyncCallback(this.OnAsyncHandlerCompletion);            }                     voidIExecutionStep.Execute()            {                HttpContext context = _application.Context;                IHttpHandler handler = context.Handler;                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Information, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_HTTPHANDLER_ENTER, context.WorkerRequest);                if (handler != null && HttpRuntime.UseIntegratedPipeline) {                    IIS7WorkerRequest wr = context.WorkerRequest as IIS7WorkerRequest;                    if (wr != null && wr.IsHandlerExecutionDenied()) {                        _sync = true;                        HttpException error = new HttpException(403, SR.GetString(SR.Handler_access_denied));                        error.SetFormatter(new PageForbiddenErrorFormatter(context.Request.Path, SR.GetString(SR.Handler_access_denied)));                        throw error;                    }                }                if (handler == null) {                    _sync = true;                }                else if (handler is IHttpAsyncHandler) {                    // asynchronous handler                    IHttpAsyncHandler asyncHandler = (IHttpAsyncHandler)handler;                    _sync = false;                    _handler = asyncHandler;                                      var beginProcessRequestDelegate = AppVerifier.WrapBeginMethod<HttpContext>(_application, asyncHandler.BeginProcessRequest);                    _asyncStepCompletionInfo.Reset();                    context.SyncContext.AllowVoidAsyncOperations();                    IAsyncResult ar;                    try {                        ar = beginProcessRequestDelegate(context, _completionCallback, null);                    }                    catch {                        // The asynchronous step has completed, so we should disallow further                        // async operations until the next step.                        context.SyncContext.ProhibitVoidAsyncOperations();                        throw;                    }                    bool operationCompleted;                    bool mustCallEndHandler;                    _asyncStepCompletionInfo.RegisterBeginUnwound(ar, out operationCompleted, out mustCallEndHandler);                    if (operationCompleted) {                        _sync = true;                        _handler = null; // not to remember                        // The asynchronous step has completed, so we should disallow further                        // async operations until the next step.                        context.SyncContext.ProhibitVoidAsyncOperations();                        try {                            if (mustCallEndHandler) {                                asyncHandler.EndProcessRequest(ar);                            }                            _asyncStepCompletionInfo.ReportError();                        }                        finally {                            SuppressPostEndRequestIfNecessary(context);                            //  In Integrated mode, generate the necessary response headers                            //  after the ASP.NET handler runs                            context.Response.GenerateResponseHeadersForHandler();                        }                        if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Information, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_HTTPHANDLER_LEAVE, context.WorkerRequest);                    }                }                else {                    //同步 handler                    _sync = true;                                       context.SyncContext.SetSyncCaller();                    try {                    handler.ProcessRequest(context);//开始Page页面生命周期                    }                    finally {                        context.SyncContext.ResetSyncCaller();                        if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Information, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_HTTPHANDLER_LEAVE, context.WorkerRequest);                        SuppressPostEndRequestIfNecessary(context);                                             context.Response.GenerateResponseHeadersForHandler();                    }                }            }            bool IExecutionStep.CompletedSynchronously {                get { return _sync;}            }            bool IExecutionStep.IsCancellable {                // launching of async handler should not be cancellable                get { return (_application.Context.Handler is IHttpAsyncHandler) ? false : true; }            }        }

13、进入Page类的 ProcessRequest方法开始处理请求

private void ProcessRequest() {        // culture needs to be saved/restored only on synchronous pages (if at all)        // save culture        Thread currentThread = Thread.CurrentThread;        CultureInfo prevCulture = currentThread.CurrentCulture;        CultureInfo prevUICulture = currentThread.CurrentUICulture;        try {            ProcessRequest(true /*includeStagesBeforeAsyncPoint*/, true /*includeStagesAfterAsyncPoint*/);//调用ProcessRequest函数        }        finally {            // restore culture            RestoreCultures(currentThread, prevCulture, prevUICulture);        }    }

14、进入ProcessRequest,调用ProcessRequestMain函数

 private void ProcessRequest(bool includeStagesBeforeAsyncPoint, bool includeStagesAfterAsyncPoint) {        // Initialize the object and build the tree of controls.        // This must happen *after* the intrinsics have been set.        // On async pages only call Initialize once (ProcessRequest is called twice)        if (includeStagesBeforeAsyncPoint) {            FrameworkInitialize();            this.ControlState = ControlState.FrameworkInitialized;        }        bool needToCallEndTrace = Context.WorkerRequest is IIS7WorkerRequest;        try {            try {                if (IsTransacted) {                    ProcessRequestTransacted();                }                else {                    // No transactions                    ProcessRequestMain(includeStagesBeforeAsyncPoint, includeStagesAfterAsyncPoint);//调用ProcessRequestMain函数                }                if (includeStagesAfterAsyncPoint) {                    needToCallEndTrace = false;                    ProcessRequestEndTrace();                }            }            catch (ThreadAbortException) {                try {                    if (needToCallEndTrace)                        ProcessRequestEndTrace();                } catch {}            }            finally {                if (includeStagesAfterAsyncPoint) {                    ProcessRequestCleanup();                }            }        }        catch { throw; }    // Prevent Exception Filter Security Issue (ASURT 122835)    }

15、进入ProcessRequestMain,开始Page页面主体处理过程

    private void ProcessRequestMain(bool includeStagesBeforeAsyncPoint, bool includeStagesAfterAsyncPoint) {        try {            HttpContext con = Context;            string exportedWebPartID = null;                            if (con.TraceIsEnabled) Trace.Write("aspx.page", "Begin PreInit");                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_PRE_INIT_ENTER, _context.WorkerRequest);                PerformPreInit(); //Page页面生命周期的OnPerLoad阶段                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_PRE_INIT_LEAVE, _context.WorkerRequest);                if (con.TraceIsEnabled) Trace.Write("aspx.page", "End PreInit");                if (con.TraceIsEnabled) Trace.Write("aspx.page", "Begin Init");                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_INIT_ENTER, _context.WorkerRequest);                InitRecursive(null);                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_INIT_LEAVE, _context.WorkerRequest);                if (con.TraceIsEnabled) Trace.Write("aspx.page", "End Init");                if (con.TraceIsEnabled) Trace.Write("aspx.page", "Begin InitComplete");                OnInitComplete(EventArgs.Empty);//Page页面生命周期的OnInitComplete阶段                if (con.TraceIsEnabled) Trace.Write("aspx.page", "End InitComplete");                if (IsPostBack) {                    if (con.TraceIsEnabled) Trace.Write("aspx.page", "Begin LoadState");                    if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_LOAD_VIEWSTATE_ENTER, _context.WorkerRequest);                    LoadAllState();//Page页面生命周期的LoadViewState阶段（加载视图状态）                    if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_LOAD_VIEWSTATE_LEAVE, _context.WorkerRequest);                    if (con.TraceIsEnabled) {                        Trace.Write("aspx.page", "End LoadState");                        Trace.Write("aspx.page", "Begin ProcessPostData");                    }                    if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_LOAD_POSTDATA_ENTER, _context.WorkerRequest);                    ProcessPostData(_requestValueCollection, true /* fBeforeLoad */);//Page页面生命周期ProcessPostData阶段（处理回发数据）                    if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_LOAD_POSTDATA_LEAVE, _context.WorkerRequest);                    if (con.TraceIsEnabled) Trace.Write("aspx.page", "End ProcessPostData");                }                if (con.TraceIsEnabled) Trace.Write("aspx.page", "Begin PreLoad");                OnPreLoad(EventArgs.Empty);//Page页面生命周期OnPreLoad阶段（预加载）                if (con.TraceIsEnabled) Trace.Write("aspx.page", "End PreLoad");                if (con.TraceIsEnabled) Trace.Write("aspx.page", "Begin Load");                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_LOAD_ENTER, _context.WorkerRequest);               LoadRecursive();//Page页面生命周期Load阶段（加载）                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_LOAD_LEAVE, _context.WorkerRequest);                if (con.TraceIsEnabled) Trace.Write("aspx.page", "End Load");                if (IsPostBack) {                    // Try process the post data again (ASURT 29045)                    if (con.TraceIsEnabled) Trace.Write("aspx.page", "Begin ProcessPostData Second Try");                   <span style="color:#FF0000;"><strong> ProcessPostData(_leftoverPostData, false /* !fBeforeLoad */);//Page页面生命周期 ProcessPostData阶段</strong></span>                    if (con.TraceIsEnabled) {                        Trace.Write("aspx.page", "End ProcessPostData Second Try");                        Trace.Write("aspx.page", "Begin Raise ChangedEvents");                    }                    if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_POST_DATA_CHANGED_ENTER, _context.WorkerRequest);                    RaiseChangedEvents();//Page页面生命周期 RaiseChangedEvents阶段（处理回发更改事件）                    if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_POST_DATA_CHANGED_LEAVE, _context.WorkerRequest);                    if (con.TraceIsEnabled) {                        Trace.Write("aspx.page", "End Raise ChangedEvents");                        Trace.Write("aspx.page", "Begin Raise PostBackEvent");                    }                    if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_RAISE_POSTBACK_ENTER, _context.WorkerRequest);                    RaisePostBackEvent(_requestValueCollection);//Page页面生命周期 RaisePostBackEvent阶段（处理回发事件）                    if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_RAISE_POSTBACK_LEAVE, _context.WorkerRequest);                    if (con.TraceIsEnabled) Trace.Write("aspx.page", "End Raise PostBackEvent");                }                if (con.TraceIsEnabled) Trace.Write("aspx.page", "Begin LoadComplete");                OnLoadComplete(EventArgs.Empty);//Page页面生命周期 加载完成                if (con.TraceIsEnabled) Trace.Write("aspx.page", "End LoadComplete");                if (IsPostBack && IsCallback) {                   PrepareCallback(callbackControlId);//Page页面生命周期 PrepareRender(预呈现)                }                else if (!IsCrossPagePostBack) {                    if (con.TraceIsEnabled) Trace.Write("aspx.page", "Begin PreRender");                    if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_PRE_RENDER_ENTER, _context.WorkerRequest);                    PreRenderRecursiveInternal();                    if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_PRE_RENDER_LEAVE, _context.WorkerRequest);                    if (con.TraceIsEnabled) Trace.Write("aspx.page", "End PreRender");                }            }            /// Async Point here            if (_legacyAsyncInfo == null || _legacyAsyncInfo.CallerIsBlocking) {                // for non-async pages with registered async tasks - run the tasks here                // also when running async page via server.execute - run the tasks here                ExecuteRegisteredAsyncTasks();            }            // Make sure RawUrl gets validated.            ValidateRawUrlIfRequired();            if (includeStagesAfterAsyncPoint) {                if (IsCallback) {                    RenderCallback();                    return;                }                if (IsCrossPagePostBack) {                    return;                }                if (con.TraceIsEnabled) Trace.Write("aspx.page", "Begin PreRenderComplete");                PerformPreRenderComplete();                if (con.TraceIsEnabled) Trace.Write("aspx.page", "End PreRenderComplete");                if (con.TraceIsEnabled) {                    BuildPageProfileTree(EnableViewState);                    Trace.Write("aspx.page", "Begin SaveState");                }                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_SAVE_VIEWSTATE_ENTER, _context.WorkerRequest);                SaveAllState();//Page页面生命周期 SaveAllState阶段（保存视图状态）                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_SAVE_VIEWSTATE_LEAVE, _context.WorkerRequest);                if (con.TraceIsEnabled) {                    Trace.Write("aspx.page", "End SaveState");                    Trace.Write("aspx.page", "Begin SaveStateComplete");                }                OnSaveStateComplete(EventArgs.Empty);                if (con.TraceIsEnabled) {                    Trace.Write("aspx.page", "End SaveStateComplete");                    Trace.Write("aspx.page", "Begin Render");                }                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_RENDER_ENTER, _context.WorkerRequest);                // Special-case Web Part Export so it executes in the same security context as the page itself (VSWhidbey 426574)                if (exportedWebPartID != null) {                    ExportWebPart(exportedWebPartID);                }                else {                    RenderControl(CreateHtmlTextWriter(Response.Output));//Page页面生命周期 Render阶段（呈现）                }                if (EtwTrace.IsTraceEnabled(EtwTraceLevel.Verbose, EtwTraceFlags.Page)) EtwTrace.Trace(EtwTraceType.ETW_TYPE_PAGE_RENDER_LEAVE, _context.WorkerRequest);                if (con.TraceIsEnabled) Trace.Write("aspx.page", "End Render");                CheckRemainingAsyncTasks(false);            }                   }

至此，整个IIS处理Asp.Net完整请求就结束了，列举了各个关键处理阶段的处理函数。当我们了解.net framework内部处理机制后能够使我们理解Asp.Net运行机制和本质，对开发人员来说这很重要，不能只停留在会用会写的阶段，而且要知道其内部原理。这样不仅可以帮助我们编写更高效的代码,同时可以学习并借鉴微软的面向对象的编程思想，受益颇多！