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Q289112: HOWTO: Initialize COM Apartment in an ISAPI Extension or Filter

Article: Q289112
Product(s): Internet Information Server
Version(s): 4.0,5.0
Operating System(s): 
Keyword(s): 
Last Modified: 03-OCT-2001

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The information in this article applies to:

- Microsoft Internet Information Server versions 4.0, 5.0 
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SUMMARY
=======

This article describes how to initialize a Component Object Model (COM)
apartment in an Internet Server API (ISAPI) extension or filter. To use a COM
component in an ISAPI filter, you need to fully understand how COM apartments
and ISAPI thread pools interact.

MORE INFORMATION
================

Internet Information Server (IIS) is a multithreaded application, and the ISAPI
extension is called on different threads for each request. When a threading
model mismatch occurs, COM creates the component in a thread of its own. This
thread inherits the credentials of the calling process, which is InetInfo.exe.
To correctly initialize the desired COM apartment in an ISAPI extension or
filter, you must create a separate thread and initialize that thread with the
required apartment.

ASP threads are initialized as apartment threads in both the IIS 4.0 and the IIS
5.0 threading models. However, to use COM in ISAPI, you should not initialize
COM or make a COM call in the GetExtensionVersion function unless you require
that these calls be made under the credentials of either the SYSTEM account (for
low-security ISAPI DLLs) or the IWAM_machinename account (for medium- or
high-security ISAPI DLLs).

You can use COM in ISAPI in the following two ways:

- Create your own thread or a thread pool in an ISAPI DLL and initialize the
  thread (or each thread in the pool) to match the threading model of the COM
  component. Then use this thread (or a thread pool) to instantiate and call
  the component.

  NOTE: Microsoft recommends that you use this procedure.

- In HttpExensionProc, call the CoInitializeEx(NULL, COINIT_MULTITHREADED)
  function and verify that this succeeds. If CoInitializeEx is successful, you
  can create, call, or release the COM component, and then call CoUninitialize
  prior to returning.

  NOTE: Microsoft does not recommend that you use this procedure.

REFERENCES
==========

For additional information, click the article numbers below to view the articles
in the Microsoft Knowledge Base:

  Q197728 Creating a Thread Pool for MFC-Based ISAPI Extensions

  Q150777 INFO: Descriptions and Workings of OLE Threading Models

  Q185518 HOWTO: Implement Worker Threads Using MFC ISAPI Extension

For more information, see the following Microsoft Web site:

  Processes, Threads, and Apartments
  http://msdn.microsoft.com/library/default.asp?url=/library/en-us/com/aptnthrd_8po3.asp?frame=true

Additional query words:

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Keywords          :  
Technology        : kbiisSearch kbiis500 kbiis400
Version           : :4.0,5.0
Issue type        : kbhowto

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