第36篇 Asp.Net源码解析(一)

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

1. 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) {
            ...
      }
      }   

2. 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

1. 首先看下ISAPIRuntime中的ProcessRequest方法签名

    public int ProcessRequest(IntPtr ecb, int iWRType);

1. 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

1. 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);
    }

1. 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) {
        ...
    }
    }

1. 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