IIS Samples - ISAPI Worker Thread

This sample demonstrates how to create and manage a worker thread pool to handle requests to this ISAPI extension so that the IIS thread pool is not depleted. This can be useful if your ISAPI takes a long time to process.

Important   These samples are provided for educational purposes only. They are not intended to be used in a production environment, have not been tested in a production environment, and Microsoft does not provide technical support for them.

 

Sample Overview
Requirements
Location of the Source Code
Build and Install the Sample
Run the Sample
Sample Output
Helpdesk

 

Sample Overview

IIS maintains a pool of threads to handle incoming HTTP requests. When all of these threads are in use, new requests will be rejected. If all the pool threads are in a wait state (for instance, running ISAPI dlls that are waiting for a query on a remote database to complete), IIS may reject incoming requests even if there is plenty of CPU power to handle them.

One way of avoiding this situation is to offload processing of these types of requests to a worker thread, releasing the IIS thread back to the pool so that it can be used for another request. This basic sample demonstrates how to implement this in an ISAPI dll.

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Requirements

This sample requires the installation of the following software to function properly:

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Location of the Source Code

IIS samples are included in the IIS Software Developer Kit (SDK). You can download the IIS SDK from Platform SDK Update. You can view the SDK at MSDN Online. In the table of contents at MSDN Online, click Web Development, Server Technologies, Internet Information Services (IIS), SDK Documentation, Internet Information Services, Samples.

The following source code files are required for this sample:

File Description
WorkerThread.sln WorkerThread Visual Studio .NET solution file, required to build this sample in Visual Studio .NET.
WorkerThread.vcproj WorkerThread Visual Studio .NET C Project file, required to build this sample in Visual Studio .NET.
WorkerThread.dsp, WorkerThread.dsw WorkerThread Visual Studio 6.0 project files, required to build this sample in Visual Studio Version 6.
WorkerThread.c WorkerThread source module containing the code that implements the sample.
WorkerThread.def WorkerThread.dll definition containing code for creating the sample.
MAKEFILE WorkerThread makefile for command line compilation

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Build and Install the Sample

To build this sample using the Visual C++ IDE, the following steps must be performed:

  1. Open the solution (VS.NET) or desktop (VS6) file to open the project.
  2. Click Build to create the DLL.

To build and run this sample without using the Visual C++ IDE, the following steps must be performed:

  1. Type NMAKE All from the command line. For example, if your sample files are located in a folder called C:\MySamples, type the following at the command line:
    cd /d c:\MySamples
    NMAKE All

 

To install this sample, the following steps must be performed:

  1. Copy WorkerThread.dll to a physical folder on your computer. For example, create a folder called C:\Samples and copy the file to that folder.
  2. Create a virtual directory that maps to the physical folder containing your files. To create a virtual directory, open the Internet Information Services (IIS) Manager by clicking Start, Run, type inetmgr in the text box and click OK. Right-click on the Web site where you want to create a virtual directory, click New, and click Virtual Directory. In the Alias text box, type the name you want for your virtual directory, for example, WorkerThread. In the Directory text box, type the path to the folder that contains your files.
  3. Configure strong security on your new virtual directory. Right-click the virtual directory name, click Properties, and click the Directory Security tab. Press F1 for tips on securing your virtual directory.
  4. Use Windows Explorer to set restricted access control on the sample .dll file in its physical folder. For more information, click Start, Help and Support, and search for Access Control.
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Run the Sample

In order to run this sample, follow the instructions listed below:

  1. Browse to your sample Web files in Internet Explorer (IE). For example, if your files are in a virtual directory called WorkerThread, type http://localhost/WorkerThread/WorkerThread.dll in the Address bar of IE.
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Sample Output

The following output is displayed somewhere after you perform step 1 from Run the Sample.

Worker Thread Sample

Send Request (button)

After you click the Send Request button, the ISAPI extension creates its own thread pool and serves the page again. To watch what the ISAPI does, run it under a debugger.

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Help Desk

If here you do not find answers to your questions, visit the Microsoft Help and Support Web site.

Problem Possible Solution
When building the dll, C++ or VB returns the a permissions error. Once you have called the dll from your web page, your system considers it a loaded dll. You must unload it to build it again, either by unloading the ASP application or deleting the dll from system32\dllcache.
When browsing to the dll, IE gives you a permissions error. The folder and virtual directory must have Execute permissions set on them.

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