ASP.NET底层原理

上图基本上演示了IIS 6整个处理过程。在User Mode下，http.sys接收到一个基于aspx的http request，然后它会根据IIS中的Metabase查看该基于该Request的Application属于哪个Application Pool，如果该Application Pool不存在，则创建之。否则直接将request发到对应Application Pool的Queue中。我上面已经说了，每个Application Pool对应着一个Worker Process：w3wp.exe，毫无疑问他是运行在User Mode下的。在IIS Metabase中维护着Application Pool和worker process的Mapping。WAS（Web Administrative service）根据这样一个mapping，将存在于某个Application Pool Queue的request 传递到对应的worker process(如果没有，就创建这样一个进程)。在worker process初始化的时候，加载ASP.NET ISAPI，ASP.NET ISAPI进而加载CLR。从而为ASP.NET Application创建一个托管的运行环境，在CLR初始化的使用会加载两个重要的dll：AppManagerAppDomainFactory和ISAPIRuntime。通过AppManagerAppDomainFactory的Create方法为Application创建一个Application Domain；通过ISAPIRuntime的ProcessRequest处理Request，进而将流程拖入到ASP.NET Http Runtime Pipeline的范畴，ASP.NET Http Runtime Pipeline对Http Request的处理是一个相对复杂的过程，相关的介绍会放在本篇文章的下一部份。在这里我们可以把它看成是一个黑盒，它接管Request，最终生成Html。

ISAPIRuntime会首先创建一个ISAPIWorkRequest对象，对请求报文进行了简单的封装，并将该ISAPIWorkRequest对象传递给HttpRuntime。

HttpRuntime会根据ISAPIWorkRequest创建用于封装Http请求上下文的对象HttpConetxt。

　　HttpContext主要包括HttpRequest（当前请求）和HttpResponse（服务器响应）

[SecurityPermission(SecurityAction.LinkDemand, Unrestricted=true)]
public int ProcessRequest(IntPtr ecb, int iWRType)
{
    IntPtr zero = IntPtr.Zero;
    if (iWRType == 2)
    {
        zero = ecb;
        ecb = UnsafeNativeMethods.GetEcb(zero);
    }
    //创建了ISAPIWorkRquest空对象
    ISAPIWorkerRequest wr = null;
    try
    {
        bool useOOP = iWRType == 1;
    //通过ecb句柄创建了ISAPIWorkRequest对象
        wr = ISAPIWorkerRequest.CreateWorkerRequest(ecb, useOOP);
        wr.Initialize();
        string appPathTranslated = wr.GetAppPathTranslated();
        string appDomainAppPathInternal = HttpRuntime.AppDomainAppPathInternal;
        if ((appDomainAppPathInternal == null) || StringUtil.EqualsIgnoreCase(appPathTranslated, appDomainAppPathInternal))
        {
        //IsapiRuntime把WR交给了HttpRuntime
            HttpRuntime.ProcessRequestNoDemand(wr);
            return 0;
        }
        HttpRuntime.ShutdownAppDomain(ApplicationShutdownReason.PhysicalApplicationPathChanged, SR.GetString("Hosting_Phys_Path_Changed", new object[] { appDomainAppPathInternal, appPathTranslated }));
        return 1;
    }
    catch (Exception exception)
    {
        try
        {
            WebBaseEvent.RaiseRuntimeError(exception, this);
        }
        catch
        {
        }
        if ((wr == null) || !(wr.Ecb == IntPtr.Zero))
        {
            throw;
        }
        if (zero != IntPtr.Zero)
        {
            UnsafeNativeMethods.SetDoneWithSessionCalled(zero);
        }
        if (exception is ThreadAbortException)
        {
            Thread.ResetAbort();
        }
        return 0;
    }
}

 

ISAPIRuntime

View Code

 HttpRuntime通过HttpApplicationFactory获取一个新的或现有的HttpApplication对象。

private void ProcessRequestInternal(HttpWorkerRequest wr)
{
    Interlocked.Increment(ref this._activeRequestCount);
    if (this._disposingHttpRuntime)
    {
        try
        {
            wr.SendStatus(0x1f7, "Server Too Busy");
            wr.SendKnownResponseHeader(12, "text/html; charset=utf-8");
            byte[] bytes = Encoding.ASCII.GetBytes("Server Too Busy");
            wr.SendResponseFromMemory(bytes, bytes.Length);
            wr.FlushResponse(true);
            wr.EndOfRequest();
        }
        finally
        {
            Interlocked.Decrement(ref this._activeRequestCount);
        }
    }
    else
    {
        HttpContext context;
        try
        {
        //通过wr创建了上下文对象
            context = new HttpContext(wr, false);
        }
        catch
        {
            try
            {
                wr.SendStatus(400, "Bad Request");
                wr.SendKnownResponseHeader(12, "text/html; charset=utf-8");
                byte[] data = Encoding.ASCII.GetBytes("Bad Request");
                wr.SendResponseFromMemory(data, data.Length);
                wr.FlushResponse(true);
                wr.EndOfRequest();
                return;
            }
            finally
            {
                Interlocked.Decrement(ref this._activeRequestCount);
            }
        }
        wr.SetEndOfSendNotification(this._asyncEndOfSendCallback, context);
        HostingEnvironment.IncrementBusyCount();
        try
        {
            try
            {
                this.EnsureFirstRequestInit(context);
            }
            catch
            {
                if (!context.Request.IsDebuggingRequest)
                {
                    throw;
                }
            }
            context.Response.InitResponseWriter();
        
        //通过HttpApplicationFactory获取HttpApplication实例
            IHttpHandler applicationInstance = HttpApplicationFactory.GetApplicationInstance(context);
            if (applicationInstance == null)
            {
                throw new HttpException(SR.GetString("Unable_create_app_object"));
            }
            if (EtwTrace.IsTraceEnabled(5, 1))
            {
                EtwTrace.Trace(EtwTraceType.ETW_TYPE_START_HANDLER, context.WorkerRequest, applicationInstance.GetType().FullName, "Start");
            }
            if (applicationInstance is IHttpAsyncHandler)
            {
                IHttpAsyncHandler handler2 = (IHttpAsyncHandler) applicationInstance;
                context.AsyncAppHandler = handler2;

            //执行HttpApplication的BeginProcessRequest方法
                handler2.BeginProcessRequest(context, this._handlerCompletionCallback, context);
            }
            else
            {
                applicationInstance.ProcessRequest(context);
                this.FinishRequest(context.WorkerRequest, context, null);
            }
        }
        catch (Exception exception)
        {
            context.Response.InitResponseWriter();
            this.FinishRequest(wr, context, exception);
        }
    }
}

HttpRuntime

View Code