vb.net code 39 generator software C11620245.fm Page 364 Wednesday, June 9, 2004 4:49 PM in .NET framework

Drawing ANSI/AIM Code 128 in .NET framework C11620245.fm Page 364 Wednesday, June 9, 2004 4:49 PM

C11620245.fm Page 364 Wednesday, June 9, 2004 4:49 PM
ANSI/AIM Code 128 Encoder In .NET Framework
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Painting Barcode In VS .NET
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Part IV
Code128 Drawer In C#.NET
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Encode Code 128A In Visual Studio .NET
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Message receivers Metabase http.sys
F11DR01
SOAP
SMTP
Figure 11-1 The WebHost architecture, which permits the flow of messages from IIS up to the ASP.NET 2.0 runtime environment
Protocol Handlers
In the context of WebHost, protocol handlers play a double role: receiving as well as dispatching messages from the queue. They connect applications with message receivers through a message queue. Each receiver captures messages of a particular type (such as HTTP, TCP, or SOAP) and places them in a protocol-specific queue. As Figure 11-1 shows, there are two kinds of protocol handlers process handlers and AppDomain handlers. A process protocol handler is a global component shared by all applications in the pool managed by the worker process. The protocol handler manages all the messages for any pooled application. An AppDomain protocol handler is a component local to each application domain that has visibility only on the messages destined for the AppDomain it lives in.
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11
The ASP.NET Runtime Environment
Walking Through an ASP.NET Request
Once in the worker process, the request is first routed through the IIS core engine that handles requests for static resources (such as HTML or JPG) and dynamic resources (such as ASP or ASPX). Requests for .aspx resources are then dispatched to the ASP.NET ISAPI extension (aspnet_isapi.dll). Thus the ASP.NET ISAPI gets information about the request and creates the process host object. The process host is responsible for hosting the CLR in the IIS 6.0 worker process and for keeping track of process protocol handlers. The ASP.NET 2.0 process host is an object living inside aspnet_isapi that implements the IProcessHost interface. Note that this interface is COM-compatible, so unmanaged hosts can implement it. (In fact, aspnet_isapi.dll is a Win32 library.) The ASP.NET process host creates the application manager the component responsible for starting, stopping, and managing all AppDomains within the worker process. The application manager acts as a common tool for pumping requests up to the AppDomains that will actually service them. The application manager also allows enumeration of currently running applications by returning an array of objects representing the state of the individual application. The programming interface of the application manager lets members manage the lifetime of objects in applications and participate in process management actions such as recycling. In ASP.NET, a request is actually executed within an AppDomain. When the application manager creates an AppDomain, its hosting environment is also created. The hosting environment is represented by an ASP.NET framework class and provides services to the application itself. Each AppDomain contains a single instance of the hosting environment class. This class provides a number of static methods that allow you to register new objects, obtain configuration information, and control the AppDomain lifetime through a reference counting mechanism. In the AppDomain, the protocol handler continuously pings the corresponding queue, and when a message representing a request for the application is found, it is picked up and processed. The processing happens in much the same way as in ASP.NET 1.x. The protocol handler obtains the request, packs it into a HttpWorkerRequest structure, and processes it, passing the object to an AppDomain-specific instance of the HttpRuntime class. Just as in ASP.NET 1.x, HttpRuntime is the entry point in the HTTP pipeline that processes an ASP.NET request. After control has passed to the HTTP pipeline, what happens is also much the same as in previous versions. The request is managed by an HTTP handler and filtered by a collection of HTTP modules. A new HTTP handler (one of a
C11620245.fm Page 366 Wednesday, June 9, 2004 4:49 PM
Part IV
Advanced Topics
handful of new internal handlers) serves images to users more effectively. Quite a few new modules are available as well. Before we go further, let s get a quick refresher on the ASP.NET runtime components.
The WebHost architecture underlies the hosting capabilities of ASP.NET. The application manager, process host, host environment, and protocol handlers are abstractions for common functionality required for hosting ASP.NET outside IIS. In ASP.NET 1.1, the hosting model wasn t rigorously defined. WebHost makes up for that. If you still can t see the big picture, you can take a look at the source code of Cassini the Microsoft s mini Web server that hosts the ASP.NET engine. You can get the source code from http://www.asp.net. The classes that form the Cassini application map almost 1:1 to the components of the WebHost framework.
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