ASP.NET初始化流程分析2

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上一篇讲了从创建应用程序域到创建ISAPIRuntime实例的过程，本篇继续讲Asp.net处理第一次请求的必要的初始化过程。

ISAPIRuntime分析

ISAPIRuntime在System.Web.Hosting中实现，它的ProcessRequest是我们处理web请求的入口。

    public int ProcessRequest(IntPtr ecb, int iWRType) {
        IntPtr pHttpCompletion = IntPtr.Zero;
        if (iWRType == WORKER_REQUEST_TYPE_IN_PROC_VERSION_2) {
            pHttpCompletion = ecb;
            ecb = UnsafeNativeMethods.GetEcb(pHttpCompletion);
        }
        ISAPIWorkerRequest wr = null;
        try {
            bool useOOP = (iWRType == WORKER_REQUEST_TYPE_OOP);
            wr = ISAPIWorkerRequest.CreateWorkerRequest(ecb, useOOP);
            wr.Initialize();
            String wrPath = wr.GetAppPathTranslated();
            String adPath = HttpRuntime.AppDomainAppPathInternal;            
            if (adPath == null ||StringUtil.EqualsIgnoreCase(wrPath, adPath)) {
                HttpRuntime.ProcessRequestNoDemand(wr);
                return 0;
            }
            else {
                 HttpRuntime.ShutdownAppDomain(ApplicationShutdownReason.PhysicalApplicationPathChanged, SR.GetString(SR.Hosting_Phys_Path_Changed, adPath, wrPath));
                 return 1;
            }
        }
        catch(Exception e) {
            try {
                WebBaseEvent.RaiseRuntimeError(e, this);
            } catch {}
            if (wr != null && wr.Ecb == IntPtr.Zero) {
                if (pHttpCompletion != IntPtr.Zero) {
                    UnsafeNativeMethods.SetDoneWithSessionCalled(pHttpCompletion);
                }
                if (e is ThreadAbortException) {
                    Thread.ResetAbort();
                }                   
                return 0;
             }
            throw;
        }
    }

注意方法的IntPtr类型的参数ecb，它是一个非托管的指针，用于传递一些必须的数据，以及最终将Response的内容返回给非托管环境ISAPI（异步方式），然后呈现给Client用户。方法中调用ISAPIWorkerRequest的静态方法CreateWorkerRequest而创建ISAPIWorkerRequest对象实例，参数分别为ecb和代表WorkerRequest类型的int参数iWRType，通过判断ecb和type类型的具体内容，来决定创建什么类型的WorkerRequest（上述类型的ISPAIWorkerRequest都继承于HttpWorkerRequest），上面的代码可以看出对不同版本的IIS进行了不同的包装，通过其Initialize方法来初始化一些基本的信息（比如：contentType, querystring的长度，filepath等相关信息）。然后调用HttpRuntime.ProcessRequestNoDemand(wr)转入HttpRuntime处理请求，最终体现在调用ProcessRequestInternal方法上。

HttpRuntime分析

Httpruntime在System.Web下实现，我们来看其处理请求的ProcessRequestInternal方法。

    private void ProcessRequestInternal(HttpWorkerRequest wr) {
        Interlocked.Increment(ref _activeRequestCount);
        if (_disposingHttpRuntime) {
            try {
                wr.SendStatus(503, "Server Too Busy");
                wr.SendKnownResponseHeader(HttpWorkerRequest.HeaderContentType, "text/html; charset=utf-8");
                byte[] body = Encoding.ASCII.GetBytes("<html><body>Server Too Busy</body></html>");
                wr.SendResponseFromMemory(body, body.Length);
                wr.FlushResponse(true);
                wr.EndOfRequest();
            } finally {
                Interlocked.Decrement(ref _activeRequestCount);
            }
            return;
        }
        HttpContext context;
        try {
            context = new HttpContext(wr, false);
        }
        catch {
            try {
                wr.SendStatus(400, "Bad Request");
                wr.SendKnownResponseHeader(HttpWorkerRequest.HeaderContentType, "text/html; charset=utf-8");
                byte[] body = Encoding.ASCII.GetBytes("<html><body>Bad Request</body></html>");
                wr.SendResponseFromMemory(body, body.Length);
                wr.FlushResponse(true);
                wr.EndOfRequest();
                return;
            } finally {
                Interlocked.Decrement(ref _activeRequestCount);
            }
        }
        wr.SetEndOfSendNotification(_asyncEndOfSendCallback, context);
        HostingEnvironment.IncrementBusyCount();
        try {
            try {
                EnsureFirstRequestInit(context);
            }
            catch {
                if (!context.Request.IsDebuggingRequest) {
                    throw;
                }
            }
            context.Response.InitResponseWriter();
            IHttpHandler app = HttpApplicationFactory.GetApplicationInstance(context);
            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) {
                IHttpAsyncHandler asyncHandler = (IHttpAsyncHandler)app;
                context.AsyncAppHandler = asyncHandler;
                asyncHandler.BeginProcessRequest(context, _handlerCompletionCallback, context);
            }
            else {
                app.ProcessRequest(context);
                FinishRequest(context.WorkerRequest, context, null);
            }
        }
        catch (Exception e) {
            context.Response.InitResponseWriter();
            FinishRequest(wr, context, e);
        }
    }

该方法中创建了熟悉的HttpContext并同时创建了HttpRequest与HttpResponse

internal HttpContext(HttpWorkerRequest wr, bool initResponseWriter) {

        _wr = wr;

        Init(new HttpRequest(wr, this), new HttpResponse(wr, this));

if (initResponseWriter)

            _response.InitResponseWriter();

        PerfCounters.IncrementCounter(AppPerfCounter.REQUESTS_EXECUTING);

    }

然后通过HttpApplicationFactory的GetApplicationInstance静态方法，获取我们熟悉的HttpApplication对象实例（注：HttpApplication对象是继承IHttpAsyncHandler，而IHttpAsyncHandler又继承于IHttpHandler），然后执行调用BeginProcessRequest方法。至此正式进入了HttpApplication对象的创建以及大家熟知的HttpApplication以后的生命周期了。

HttpApplicationFactory分析

HttpApplicationFactory在System.Web下实现。

查看HttpApplicationFactory用来创建Httpapplication的GetApplicationInstance方法。

    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);
    }

该方法有三个步骤：首先是EnsureInited，会检查是否已经初始化，如果没有会调用Init方法先获取global.asax文件的完整路径，然后调用CompileApplication()对global.asax进行编译，Init方法如下。

    private void Init() {
        if (_customApplication != null)
            return;
        try {
            try {
                _appFilename = GetApplicationFile();
                CompileApplication();
             }
            finally {
                SetupChangesMonitor();
            }
        }
        catch {
            throw;
        }
}

然后是EnsureAppStartCalled方法如果未开始启动会调用FireApplicationOnStart。

   private void EnsureAppStartCalled(HttpContext context) {
        if (!_appOnStartCalled) {
            lock (this) {
                if (!_appOnStartCalled) {
                    using (new DisposableHttpContextWrapper(context)) {
                        WebBaseEvent.RaiseSystemEvent(this, WebEventCodes.ApplicationStart);
                        FireApplicationOnStart(context);
                        }
                    _appOnStartCalled = true;
                }
            }
        }
    }

    private void FireApplicationOnStart(HttpContext context) {
        if (_onStartMethod != null) {
            HttpApplication app = GetSpecialApplicationInstance();
            app.ProcessSpecialRequest(context, _onStartMethod, _onStartParamCount, this, EventArgs.Empty, null);
            RecycleSpecialApplicationInstance(app);
        }
    }

这里创建特定的HttpApplication实例，触发ApplicationOnStart事件(会执行global.asax中的Application_Start方法)。然后在处理完事件以后就立即被回收掉，因为系统初始化只需要一次。

最后是GetNormalApplicationInstance，如果在有空闲的HttpApplication实例，就直接用，如果没有就新创建，然后调用InitInternal方法进行初始化相关的内容，最后返回该HttpApplication实例。

    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) {
            app = (HttpApplication)HttpRuntime.CreateNonPublicInstance(_theApplicationType);
            using (new ApplicationImpersonationContext()) {
                app.InitInternal(context, _state, _eventHandlerMethods);
            }
        }
        ……
        return app;
    }

HttpApplication分析

HttpApplication在System.Web下实现，首先查看HttpApplication的InitInternal方法，该方法用于初始化。

    internal void InitInternal(HttpContext context, HttpApplicationState state, MethodInfo[] handlers) {
        Debug.Assert(context != null, "context != null");
        _state = state;
        PerfCounters.IncrementCounter(AppPerfCounter.PIPELINES);
        try {
            try {
                _initContext = context;
                _initContext.ApplicationInstance = this;
                context.ConfigurationPath = context.Request.ApplicationPathObject;
                using (new DisposableHttpContextWrapper(context)) {
                    if (HttpRuntime.UseIntegratedPipeline) {
                        Debug.Assert(_moduleConfigInfo != null, "_moduleConfigInfo != null");
                        Debug.Assert(_moduleConfigInfo.Count >= 0, "_moduleConfigInfo.Count >= 0");
                        try {
                            context.HideRequestResponse = true;
                            _hideRequestResponse = true;
                            InitIntegratedModules();
                        }
                        finally {
                            context.HideRequestResponse = false;
                            _hideRequestResponse = false;
                        }
                    }
                    else {
                        InitModules();
                        Debug.Assert(null == _moduleContainers, "null == _moduleContainers");
                    }
                    if (handlers != null)
                        HookupEventHandlersForApplicationAndModules(handlers);
                    _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);
                if (HttpRuntime.UseIntegratedPipeline) {
                    _stepManager = new PipelineStepManager(this);
                }
                else {
                    _stepManager = new ApplicationStepManager(this);
                }
                _stepManager.BuildSteps(_resumeStepsWaitCallback);
            }
            finally {
                _initInternalCompleted = true;
                context.ConfigurationPath = null;
                _initContext.ApplicationInstance = null;
                _initContext = null;
            }
        }
        catch {
            throw;
        }
    }

该代码主要有2个功能，一个是初始化大家熟悉的HttpModules，一个是通过BuildSteps执行多个生命周期事件的处理函数。通过上面的代码我们可以看出，每个功能都有一个特殊判断，判断IIS是否是IIS7的集成模式，如果是就有特殊的步骤，如果不是就走一般的步骤（两者直接的差异分别是：经典模式初始化HttpModules的时候会从网站配置的Modules里读取，集成模式会预加载CLR和大量Modules，比如加载服务器上设置的HttpModules；另外在BuildSteps的时候， IIS7集成模式走的是自己特殊的流程）。

总结一下，InitInternal方法的主要功能如下：

InitModules()：根据Web.Config的设置，加载相应的HttpModules。

InitIntegratedModules()：会加载IIS7集成模式下在服务器上设定的HttpModuels和Web.config里system.webserver下的HttpModuels。

HookupEventHandlersForAppplicationAndModules：绑定HttpApplication实例中相应的事件处理函数（在Global.asax中定义的事件处理函数）。

创建很多实现IExecutionStep接口的类的实例并添加到当前HttpApplication实例的_execSteps中（包括HttpModules中定义的周期事件处理函数和查找匹配的HttpHandler、执行HttpHandler的方法以及过滤输出等特殊事件），等待回调时执行。从这里我们可以看到HttpApplication是以异步的方式处理请求，对请求的很多处理工作都放入了_execStep等待回调时执行。

在 HttpApplication的事件如下形式定义：

    public event EventHandler BeginRequest {
        add { AddSyncEventHookup(EventBeginRequest, value, RequestNotification.BeginRequest); }
        remove { RemoveSyncEventHookup(EventBeginRequest, value, RequestNotification.BeginRequest); }
    }

所有的事件都是调用AddSyncEventHookup方法添加进去的，其中第一个参数是以Event+事件名称的值。

    internal void AddSyncEventHookup(object key, Delegate handler, RequestNotification notification) {
        AddSyncEventHookup(key, handler, notification, false);
    }
    private void AddSyncEventHookup(object key, Delegate handler, RequestNotification notification, bool isPostNotification) {
        ThrowIfEventBindingDisallowed();
        Events.AddHandler(key, handler);
        if (IsContainerInitalizationAllowed) {
            PipelineModuleStepContainer container = GetModuleContainer(CurrentModuleCollectionKey);
            if (container != null) {
                SyncEventExecutionStep step = new SyncEventExecutionStep(this, (EventHandler)handler);
                container.AddEvent(notification, isPostNotification, step);
            }
        }
    }

经典模式下在初始化HttpModlue的时候通过调用Events.AddHandler方法，将事件添加到Events集合里，同时这个key就是Event+事件名称，而集成模式下这些事件是添加到另外一个地方的（通过将事件hanlder包装成SyncEventExecutionStep类型，然后调用container.AddEvent方法将事件添加到另外一个地方），也就是说if上面的Events集合是给经典模式用的，下面的Container里的数据是给集成模式用的，这些事件是存放在HttpApplication的ModuleContainers属性里，这个属性的类型是PipelineModuleStepContainer[]，个数就是HttpModules的个数，也就是说每个HttpModule在HttpApplication上添加的事件都放在各自的PipelineModuleStepContainer容器里。

    private PipelineModuleStepContainer[] ModuleContainers {
        get {
            if (_moduleContainers == null) {
                Debug.Assert(_moduleIndexMap != null && _moduleIndexMap.Count > 0, "_moduleIndexMap != null && _moduleIndexMap.Count > 0");
                _moduleContainers = new PipelineModuleStepContainer[_moduleIndexMap.Count];
                for (int i = 0; i < _moduleContainers.Length; i++) {
                    _moduleContainers[i] = new PipelineModuleStepContainer();
                }
            }
            return _moduleContainers;
        }
}

StepManager分析

集成模式和经典模式（或IIS6）使用的是不同的StepManager，这个类的BuildSteps方法就是为了创建有序的ExecutionStep，其中包括各种事件的事情以及其它在各时间周期之间穿插的操作，最主要的操作，大家以前就应该知道的，比如哪个周期可以判定使用哪个HttpHandler，以及在哪个周期内执行这个HttpHandler的BeginProcessRequest方法。StepManager的具体实现类（ApplicationStepManager、PipelineStepManager）和HttpApplication类在同一个文件中定义。

ApplicationStepManager的BuildSteps方法（用于经典模式）

    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));     // map 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());        
        steps.Add(new CallHandlerExecutionStep(app)); // execute handler       
        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);
        _resumeStepsWaitCallback = stepCallback;
    }

    private void CreateEventExecutionSteps(Object eventIndex, ArrayList steps) {
        AsyncAppEventHandler asyncHandler = AsyncEvents[eventIndex];
        if (asyncHandler != null) {
            asyncHandler.CreateExecutionSteps(this, steps);
        }
        EventHandler handler = (EventHandler)Events[eventIndex];
        if (handler != null) {
            Delegate[] handlers = handler.GetInvocationList();
            for (int i = 0; i < handlers.Length; i++)  {
                steps.Add(new SyncEventExecutionStep(this, (EventHandler)handlers[i]));
            }
         }
    }

这个方法的完整功能归纳总结有以下几点：

对请求的Request进行验证，ValidateRequestExecutionStep。

对请求的路径进行安全检查，禁止非法路径访问(ValidatePathExecutionStep)。　

如果设置了UrlMappings, 进行RewritePath(UrlMappingsExecutionStep)。

执行事件处理函数，比如将BeginRequest、AuthenticateRequest转化成可执行ExecutionStep在正式调用时候执行。

在这多个个事件操作处理期间，根据不同的时机加了4个特殊的ExecutionStep。

MapHandlerExecutionStep：查找匹配的HttpHandler

CallHandlerExecutionStep：执行HttpHandler的BeginProcessRequest

CallFilterExecutionStep：调用Response.FilterOutput方法过滤输出

NoopExecutionStep：空操作，留着以后扩展用

所有的ExecuteionStep都保存在ApplicationStepManager实例下的私有字段_execSteps里，而HttpApplication的BeginProcessRequest方法最终会通过该实例的ResumeSteps方法来执行这些操作。

PipelineStepManager的BuildSteps（用于集成模式）

    internal override void BuildSteps(WaitCallback stepCallback) {
        Debug.Trace("PipelineRuntime", "BuildSteps");
        HttpApplication app = _application;
        IExecutionStep materializeStep = new MaterializeHandlerExecutionStep(app);
        app.AddEventMapping(ttpApplication.IMPLICIT_HANDLER,
                    RequestNotification.MapRequestHandler,
                    false, materializeStep);
        app.AddEventMapping(HttpApplication.IMPLICIT_HANDLER,
                    RequestNotification.ExecuteRequestHandler,
                    false, app.CreateImplicitAsyncPreloadExecutionStep());
        IExecutionStep handlerStep = new CallHandlerExecutionStep(app);
        app.AddEventMapping(HttpApplication.IMPLICIT_HANDLER,
                    RequestNotification.ExecuteRequestHandler,
                    false, handlerStep);
        IExecutionStep webSocketsStep = new TransitionToWebSocketsExecutionStep(app);
        app.AddEventMapping(HttpApplication.IMPLICIT_HANDLER,
                    RequestNotification.EndRequest,
                    true, webSocketsStep);
        IExecutionStep filterStep = new CallFilterExecutionStep(app);
        app.AddEventMapping(HttpApplication.IMPLICIT_FILTER_MODULE,
                    RequestNotification.UpdateRequestCache,
                    false, filterStep);
        app.AddEventMapping(HttpApplication.IMPLICIT_FILTER_MODULE,
                    RequestNotification.LogRequest,
                    false, filterStep);
        _resumeStepsWaitCallback = stepCallback;
    }

    private void AddEventMapping(string moduleName,RequestNotification requestNotification, bool isPostNotification,IExecutionStep step) {
        ......
        PipelineModuleStepContainer container = GetModuleContainer(moduleName);
        container.AddEvent(requestNotification, isPostNotification, step);
    }

以上代码有2个地方和经典模式不相同：

集成模式没有使用MapHandlerExecutionStep来装载ExecutionStep（也就是查找对应的HttpHandler），而是通过MaterializeHandlerExecutionStep类来获得HttpHandler，方式不一样。

集成模式是通过HttpApplication的AddEventMapping方法来添加事件的，从而将事件加入到前面所说的ModuleContainers容器。

总结一下，在经典模式下，是用 Event+事件名称做key将所有事件的保存在HttpApplication的Events属性对象里，然后在BuildSteps里统一按照顺序组装，中间加载4个特殊的ExecutionStep，最后在统一执行；在集成模式下，是通过HttpModule名称+RequestNotification枚举值作为key将所有的事件保存在HttpApplication的ModuleContainers属性对象里，然后也在BuildSteps里通过伪造HttpModule名称加载那4个特殊的ExecutionStep，最后按照枚举类型的顺序，遍历所有的HttpModule按顺序来执行这些事件，可以自行编写一个自定义的HttpModuel来执行这些事件看看效果如何。

下面是总结一下处理第一次请求的大体处理流程。