Asynchronous Handlers in ASP.NET

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HTTP Handlers

• An ASP.NET HTTP handler is a process, which runs in response to a request made to an ASP.NET web application.

Handler Description

.aspx Default handler for all ASP.NET Web Pages

.asmx Default handler for all Web Service Pages

.ashx Default handler for all Web Handlers, that have no UI, instead have @WebHandler directive

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Hierarchy

IHttpHandler interfacevoid ProcessRequest(HttpContext ctx); bool IsReusable {get;}

IHttpAsyncHandler : IHttpHandler IAsyncResult BeginProcessRequest(HttpContext ctx, AsyncCallback cb, object obj); void EndProcessRequest(IAsyncResult ar);

Implemented By Synchronous Handler Implemented By Asynchronous Handler

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Synchronous Handler

• A synchronous handler returns only after complete processing of the HTTP request, for which it is called.

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Synchronous Handler

CLIENT

THREAD POOL

R1

T1

REQUEST QUEUE

ERROR 503

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Registering Http Handler in Web.Config file

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Asynchronous Handlers

• Asynchronous programming helps in better usage of resources.

• In ASP.Net when a request is made, a thread is created and allocated to the handler file. the thread will be idle when the file will undergo i/o processing.

• So to properly use the thread's idle time , we can release the thread back to thread pool after passing the execution to handler file.

• When the I/O operation is complete, the framework reassigns a thread to the request and the handler can render the output to the browser.

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Asynchronous HandlerCLIENT

BEGIN

THREAD POOL

END

I/O PROCESS

Thread 1

Thread 2

Thread 1 Released

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IAsyncResult

• An asynchronous HTTP Handler uses an IAsyncResult object to notify when the operation has been completed.

• Once the I/O or DB operation is completed, thread is reassigned, ASP.NET will continue the execution of the handler.

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IsReusable Property

• If the handler returns static content, it is safe to be reusable. But if the handler returns dynamic content, to make it thread safe, IsReusable property should be set as false.

• In such case, context switching may occur, which may cause the handler to give wrong output.

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• The verb=”*” attribute, we instruct the handler to process a request that uses any verb(for eg. POST,HEAD,GET, and so on.)

• In the path=“*.sync” attribute, we instruct the handler to process any incoming requests for files with the .sync extension.

• Type=“handler class name”

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HTTPContext

• Encapsulates all HTTP-specific information about an individual HTTP request.

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Register Http Handler in Web.Config File

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If registration of Handler is not done in Web.Config File

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Now Handler is registered for *.jpg in Web.Config File

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