第36篇 Asp.Net源码解析(二)--详解HttpApplication
上次说到获得HttpApplication对象的创建，创建完成后调用InitInternal方法，这个方法任务比较多，也比较长，这里就不贴全码了，一个一个过程的去说：
初始化HttpModule
对于HttpModule的认识，首先应该看下HttpModule的使用情况，下面通过一个简单的例子展示：
httpModule使用实例
- 新建一个项目，添加一个webform的窗体default.aspx，使用IIS添加到网站，应用程序池使用集成模式。
- 添加一个MyModule.cs,继承自IHttpModule。
在IHttpMoudule中有两个方法，在MyModule中必须要实现：
public void Init(HttpApplication context) { throw new System.NotImplementedException(); } public void Dispose() { throw new System.NotImplementedException(); }在Init方法中，有一个HttpApplication类型的对象context，这里可以对其中的响应的内容进行更改，修改如下：
public void Init(HttpApplication context) { context.EndRequest += Context_EndRequest; } private void Context_EndRequest(object sender, System.EventArgs e) { var context = (HttpApplication) sender; context.Response.Write("<h1>Hello MyModule</h1>"); }添加web.config文件如下(在 system.webServer下 modules节点下面):
<add name="MyModule" type="Application.MyModule,Application"/>运行结果：
在上面的例子中，使用的是集成模式，当改成经典模式的时候，module又不起作用了。对于经典模式的配置文件与集成模式不同。经典模式的配置文件如下：
<httpModules> <add name="MyModule" type="IISIntegratedPipeline.MyModule,IISIntegratedPipeline"/> </httpModules>对于 module的使用，有了一个简单的认识，在asp.net中module是一个灵活的配置，可以对请求进行自定义的处理，对于Asp.net如何处理的，在下面详细解说。
asp.net中HttpModule的处理
结合上面例子，HttpModule在Asp.net中有重要的作用，可以HttpApplication的事件进行订阅，也可以修改对应的响应的内容
对于HttpModule的初始化,asp.Net中会根据当前应用程序池的类型进行初始化，核心代码如下：
if (HttpRuntime.UseIntegratedPipeline) { try { context.HideRequestResponse = true; _hideRequestResponse = true; InitIntegratedModules(); } finally { context.HideRequestResponse = false; _hideRequestResponse = false; } } else { InitModules(); }- 对于Module的理解，需要根据应用程序池的模式来处理（经典和集成）。
对于集成模式，获得所有Modules的方法是调用非托管的方法的进行获得，具体获得的代码如下:
InitIntegratedModules的方法
private void InitIntegratedModules() { _moduleCollection = BuildIntegratedModuleCollection(_moduleConfigInfo); InitModulesCommon(); }_moduleConfigInfo 的来源
这个_moduleConfigInfo的来源，还需要追到上篇 HttpApplication中三个方法的调用（EnsureAppStartCalled 第二个方法的调用）具体调用步骤如下：
``` C# [DllImport(_IIS_NATIVE_DLL)] internal static extern int MgdGetModuleCollection( IntPtr pConfigSystem, IntPtr appContext, out IntPtr pModuleCollection, out int count); ```对于经典模式获得Modules简单的多，直接获得是调用配置文件
private void InitModules() { HttpModulesSection pconfig = RuntimeConfig.GetAppConfig().HttpModules; // get the static list, then add the dynamic members HttpModuleCollection moduleCollection = pconfig.CreateModules(); HttpModuleCollection dynamicModules = CreateDynamicModules(); moduleCollection.AppendCollection(dynamicModules); _moduleCollection = moduleCollection; // don"t assign until all ops have succeeded InitModulesCommon(); }最终会调用 InitModulesCommon方法,循环调用Modules中的方法
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); } _currentModuleCollectionKey = null; InitAppLevelCulture(); }
Global内的方法调用
对于Global方法的调用，是调用HookupEventHandlersForApplicationAndModules(handlers);方法，这里的Handlers的收集和创建来源于上篇讲HttpAplication的三个方法调用的第一个方法。具体的看下上次的代码，这里不多叙述。对于方法的handlers的调用的核心代码如下,其实也是一个循环加上判断：
for (int i = 0; i < handlers.Length; i++) {
MethodInfo appMethod = handlers[i];
String appMethodName = appMethod.Name;
int namePosIndex = appMethodName.IndexOf("_");
String targetName = appMethodName.Substring(0, namePosIndex);
...
ParameterInfo[] addMethodParams = addMethod.GetParameters();
if (addMethodParams.Length != 1)
continue;
Delegate handlerDelegate = null;
ParameterInfo[] appMethodParams = appMethod.GetParameters();
...
try {
addMethod.Invoke(target, new Object[1]{handlerDelegate});
}
catch {
if (HttpRuntime.UseIntegratedPipeline) {
throw;
}
}
if (eventName != null) {
if (_pipelineEventMasks.ContainsKey(eventName)) {
if (!StringUtil.StringStartsWith(eventName, "Post")) {
_appRequestNotifications |= _pipelineEventMasks[eventName];
}
else {
_appPostNotifications |= _pipelineEventMasks[eventName];
}
}
}
}
根据应用程序池的类型创建不同的_stepManager
这里很简单，直接看代码：
// Construct the execution steps array
if (HttpRuntime.UseIntegratedPipeline) {
_stepManager = new PipelineStepManager(this);
}
else {
_stepManager = new ApplicationStepManager(this);
}执行BuildStep
BuildStep与ResumeStep是Asp.net的核心运行环节。同样，在经典模式与集成模式下原理和过程也有所不一样。
集成模式
下面先讨论集成模式下是如何进行的。
internal override void BuildSteps(WaitCallback stepCallback) { HttpApplication app = _application; IExecutionStep materializeStep = new MaterializeHandlerExecutionStep(app); app.AddEventMapping( HttpApplication.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 /* isPostNotification */, 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; }上面的代码是核心是AddEventMapping方法，把相关的步骤添加到一个PipelineModuleStepContainer.
private void AddEventMapping(string moduleName,RequestNotification requestNotification,bool isPostNotification, IExecutionStep step) { ThrowIfEventBindingDisallowed(); if (!IsContainerInitalizationAllowed) { return; } PipelineModuleStepContainer container = GetModuleContainer(moduleName); if (container != null) { container.AddEvent(requestNotification, isPostNotification, step); } }
经典模式
1.看下代码：
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()); // implict async preload step
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;
}
对于上面的代码，可以看出都调用了 CreateEventExecutionSteps 方法，这个方法的详细如下 ：
private void CreateEventExecutionSteps(Object eventIndex, ArrayList steps) {
// async
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]));
}
}
}可以看出， CreateEventExecutionSteps是把注册的步骤都转换成了SyncEventExecutionStep，最终会被按顺序进行调用。
执行BeginProcessRequest
HttpApplication在完成BuildSteps的时候，把生成的App经过层层返回到HttpRuntime,前面几篇文章提到，在HttpRuntime里面有对app的类型进行判断，如果是IHttpAsyncHandler直接调用BeginProcessRequest方法，具体的代码如下：
if (app is IHttpAsyncHandler) {
IHttpAsyncHandler asyncHandler = (IHttpAsyncHandler)app;
context.AsyncAppHandler = asyncHandler;
asyncHandler.BeginProcessRequest(context, _handlerCompletionCallback, context);
}
else {
// synchronous handler
app.ProcessRequest(context);
FinishRequest(context.WorkerRequest, context, null);
}
BeginProcessRequest 方法：
IAsyncResult IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) {
HttpAsyncResult result;
_context = context;
_context.ApplicationInstance = this;
_stepManager.InitRequest();
_context.Root();
result = new HttpAsyncResult(cb, extraData);
AsyncResult = result;
if (_context.TraceIsEnabled)
HttpRuntime.Profile.StartRequest(_context);
ResumeSteps(null);
return result;
}
其中最核心的方法是ResumeSteps方法，具体如下：
internal override void ResumeSteps(Exception error)
{
for (; ; ) {
// ...
IExecutionStep step = _application.CurrentModuleContainer.GetNextEvent(context.CurrentNotification, context.IsPostNotification,context.CurrentModuleEventIndex);
context.SyncContext.Enable();
stepCompletedSynchronously = false;
//*******
error = _application.ExecuteStep(step, ref stepCompletedSynchronously);
//*********
...
if (!stepCompletedSynchronously) {
_application.AcquireNotifcationContextLock(ref locked);
context.NotificationContext.PendingAsyncCompletion = true;
break;
}
else {
context.Response.SyncStatusIntegrated();
}
}
}BeginProcessRequest 方法：
IAsyncResult IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData) {
HttpAsyncResult result;
_context = context;
_context.ApplicationInstance = this;
_stepManager.InitRequest();
_context.Root();
result = new HttpAsyncResult(cb, extraData);
AsyncResult = result;
if (_context.TraceIsEnabled)
HttpRuntime.Profile.StartRequest(_context);
ResumeSteps(null);
return result;
}其中最核心的方法是ResumeSteps方法，具体如下：
internal override void ResumeSteps(Exception error)
{
...
for (; ; ) {
// ...
IExecutionStep step = _application.CurrentModuleContainer.GetNextEvent(context.CurrentNotification, context.IsPostNotification,context.CurrentModuleEventIndex);
context.SyncContext.Enable();
stepCompletedSynchronously = false;
//*******
error = _application.ExecuteStep(step, ref stepCompletedSynchronously);
//*********
...
if (!stepCompletedSynchronously) {
_application.AcquireNotifcationContextLock(ref locked);
context.NotificationContext.PendingAsyncCompletion = true;
break;
}
else {
context.Response.SyncStatusIntegrated();
}
}
}对于上面的内容总结原理为：
写于 2017.03.21
声明：该文观点仅代表作者本人，牛骨文系教育信息发布平台，牛骨文仅提供信息存储空间服务。
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