How To Initialize a COM Apartment in an ISAPI Extension or Filter (289112)


The information in this article applies to:

  • Microsoft Internet Information Server 4.0
  • Microsoft Internet Information Server 5.0
This article was previously published under Q289112
We strongly recommend that all users upgrade to Microsoft Internet Information Services (IIS) version 6.0 running on Microsoft Windows Server 2003. IIS 6.0 significantly increases Web infrastructure security. For more information about IIS security-related topics, visit the following Microsoft Web site:

http://www.microsoft.com/technet/security/prodtech/IIS.mspx

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:

197728 Creating a Thread Pool for MFC-Based ISAPI Extensions

150777 INFO: Descriptions and Workings of OLE Threading Models

185518 How To 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

Modification Type:MinorLast Reviewed:6/23/2005
Keywords:kbhowto KB289112
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