第36篇 Asp.Net源码解析(一)

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上面两篇文章说了http协议和IIS处理，这次说下当IIS把请求交给Asp.net后的过程。

AppManagerAppDomainFactory

当IIS把请求交给asp.net时候，如果AppDomain还不存在则创建APPDomain，将AppDomain指派给与请求对应的应用程序，这通过AppManagerAppDomainFactory类中的Create方法实现，代码如下：

    public Object Create(String appId, String appPath) {       try {           if (appPath[0] == '.') {               System.IO.FileInfo file = new System.IO.FileInfo(appPath);               appPath = file.FullName;           }           if (!StringUtil.StringEndsWith(appPath, '\\')) {               appPath = appPath + "\\";           }           ...           ISAPIApplicationHost appHost = new ISAPIApplicationHost(appId, appPath,false);           //创建环境，包括编译环境           ISAPIRuntime isapiRuntime = (ISAPIRuntime)_appManager.CreateObjectInternal(appId, typeof(ISAPIRuntime), appHost,  false, null);           isapiRuntime.StartProcessing();           return new ObjectHandle(isapiRuntime);       }       catch (Exception e) {             ...       }   }

创建完成后，非托管代码开始调用 ISAPIRuntime 中ProcessRequest方法(通过COM调用 )

ISAPIRuntime--asp.net入口

首先看下ISAPIRuntime中的ProcessRequest方法签名

    public int ProcessRequest(IntPtr ecb, int iWRType);

ProcessRequest有两个参数，一个是请求报文的ecb句柄，一个请求的类型，在运行的过程中，ecb首先被再次封装成托管资源的请求报文wr。把封装好的代码传递给HttpRuntime类中的ProcessRequestNoDemand. 核心代码如下：

    bool useOOP = (iWRType == WORKER_REQUEST_TYPE_OOP);    wr = ISAPIWorkerRequest.CreateWorkerRequest(ecb, useOOP);    wr.Initialize();    // check if app path matches (need to restart app domain?)                    String wrPath = wr.GetAppPathTranslated();    String adPath = HttpRuntime.AppDomainAppPathInternal;    if (adPath == null ||        StringUtil.EqualsIgnoreCase(wrPath, adPath))    {        HttpRuntime.ProcessRequestNoDemand(wr);        return 0;    }    else    {        // need to restart app domain        HttpRuntime.ShutdownAppDomain(ApplicationShutdownReason.PhysicalApplicationPathChanged,                                    SR.GetString(SR.Hosting_Phys_Path_Changed,                                                                        adPath,                                                                        wrPath));        return 1;    }

HttpRuntime

HttpRuntime收到传递过来的HttpWorkerRequest类的实例对象wr,通过调用当前类中的ProcessRequestNow方法，把参数传递给ProcessRequestInternal（ProcessRequestNow的调用了ProcessRequestInternal）。

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

在ProcessRequestInternal中，创建了HttpContext和HttpApplication对象实例，核心代码如下

    private void ProcessRequestInternal(HttpWorkerRequest wr) {        ...    // Construct the Context on HttpWorkerRequest, hook everything together    HttpContext context;    try {        context = new HttpContext(wr, false /* initResponseWriter */);    }     catch {        ...    }    ...    try {            ...        // Get application instance        IHttpHandler app = HttpApplicationFactory.GetApplicationInstance(context);        if (app == null)            throw new HttpException(SR.GetString(SR.Unable_create_app_object));            ...         if (app is IHttpAsyncHandler) {            // asynchronous handler            IHttpAsyncHandler asyncHandler = (IHttpAsyncHandler)app;            context.AsyncAppHandler = asyncHandler;            asyncHandler.BeginProcessRequest(context, _handlerCompletionCallback, context);        }        else {            // synchronous handler            app.ProcessRequest(context);            FinishRequest(context.WorkerRequest, context, null);        }    }    catch (Exception e) {        ...    }   }

在ProcessRequestInternal方法的内部，实现对HttpContext类和HttpApplicationFactory的对象实例的创建，核心代码: 根据上面代码，当获得HttApplication对象后，判断是否是IHttpAsyncHandler类型，如果是则调用BeginProcessRequest方法，此处的if条件是一直成立的，因为HttpApplication实现了IHttpAsyncHandler接口,而ProcessRequest方法的实现也仅仅是抛出了一个异常，笔者觉得此处应该是微软留了一个扩展的地方。
```
   public class HttpApplication:IComponent,IHttpAsyncHandler, IRequestCompletedNotifier, ISyncContext {        ...    }
```
```
   void IHttpHandler.ProcessRequest(HttpContext context) {            throw new HttpException(SR.GetString(SR.Sync_not_supported));        }
```

HttpContext对象

这个对象是一个请求响应的结合体，里面包含了HttpRequest和HttpResponse对象，在构造HttpContext对象时，同时也对HttpRequest和HttpResponse也进行了初始化，代码如下：

   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);    }

创建HttpApplication

通过HttpApplicationFactory中的静态方法GetApplicationInstance来获得实例对象（常用的工厂模式），在创建对象的时候调用了 _theApplicationFactory.GetNormalApplicationInstance(context);方法(其中context形参是上文创建的HttpContext）来执行实例化操作，核心代码如下：

  internal static IHttpHandler GetApplicationInstance(HttpContext context) {       if (_customApplication != null)           return _customApplication;       // Check to see if it's a debug auto-attach request       if (context.Request.IsDebuggingRequest)           return new HttpDebugHandler();              _theApplicationFactory.EnsureInited();       _theApplicationFactory.EnsureAppStartCalled(context);       return _theApplicationFactory.GetNormalApplicationInstance(context);   }

这个方法里有三个方法的调用，分别是：

i. _theApplicationFactory.EnsureInited()

主要功能是对Global.asxc文件进行编译和处理，并反射出对其中的事件，放到ArrayList中，核心代码如下：

找到global.asax路径进行编译

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

调用ReflectOnApplicationType方法把事件装入ArrayList

   private void CompileApplication() {           _theApplicationType = BuildManager.GetGlobalAsaxType();            BuildResultCompiledGlobalAsaxType result = BuildManager.GetGlobalAsaxBuildResult();            if (result != null) {                if (result.HasAppOrSessionObjects) {                    GetAppStateByParsingGlobalAsax();                }                _fileDependencies = result.VirtualPathDependencies;            }            if (_state == null) {                _state = new HttpApplicationState();            }            ReflectOnApplicationType();        }

    private void ReflectOnApplicationType() {        ArrayList handlers = new ArrayList();        MethodInfo[] methods;        // get this class methods        methods = _theApplicationType.GetMethods(BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static);        foreach (MethodInfo m in methods) {            if (ReflectOnMethodInfoIfItLooksLikeEventHandler(m))                handlers.Add(m);        }        Type baseType = _theApplicationType.BaseType;        if (baseType != null && baseType != typeof(HttpApplication)) {            methods = baseType.GetMethods(BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static);            foreach (MethodInfo m in methods) {                if (m.IsPrivate && ReflectOnMethodInfoIfItLooksLikeEventHandler(m))                    handlers.Add(m);            }        }        _eventHandlerMethods = new MethodInfo[handlers.Count];        for (int i = 0; i < _eventHandlerMethods.Length; i++)            _eventHandlerMethods[i] = (MethodInfo)handlers[i];    }

ii. _theApplicationFactory.EnsureAppStartCalled(context)

创建特定的HttpApplication实例，触发ApplicationOnStart事件，执行ASP.global_asax中的Application_Start(object sender, EventArgs e)方法。这里创建的HttpApplication实例在处理完事件后，就被回收。具体实现：

private void EnsureAppStartCalled(HttpContext context) { if (!_appOnStartCalled) {     lock (this) {       if (!_appOnStartCalled) {          using (new DisposableHttpContextWrapper(context)) {               // impersonation could be required (UNC share or app credentials)               WebBaseEvent.RaiseSystemEvent(this, WebEventCodes.ApplicationStart);               // fire outside of impersonation as HttpApplication logic takes               // care of impersonation by itself               FireApplicationOnStart(context);           }           _appOnStartCalled = true;        }     }   } }

iii. _theApplicationFactory.GetNormalApplicationInstance(context);

主要是获得HttpApplication实例，首先从队列中去取，如果取出为空，则利用反射创建，调用InitInternal方法

 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()) {                // 调用BuildSteps和获得所有的HttpModule                 app.InitInternal(context, _state, _eventHandlerMethods);             }         }         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;     }

从代码中可以分析到,在HttpApplication创建的过程中，是有一个_freeList的一个堆栈来控制的。当对象创建成功后，执行app.InitInternal(context, _state, _eventHandlerMethods)来进行后续的操作。整个的代码流程，可以理解成以下过程：

源码git地址：https://github.com/fuwei199006/Source/tree/master/dotnet46/Source

写于 2017.03.07

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