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第36篇 Asp.Net源码解析(一)

2017-03-07 16:53 603 查看
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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