Internet server extensions and filters need to be threadsafe. Please note that MFC's CRecordSet class is not threadsafe. Your extension might run some time (especially if you have set synchronous mode), but it surely will crash both itself and IIS as soon as there is sufficient workload.

This problem persists at least up to version 4.10 of VC++ (have a look at the readme sections in the info viewer - it's displayed there quite prominently). It has been reported to us that VC++ 4.20 will have this fixed. We could not confirm this ourselfs as we currently do not have this version available.

A proper alternative is to use the native ODBC API. In this case its totally up to your application to handle threadsafe coding. Please note that native ODBC doesn't mean a large burden for specialised applications (which probably your extension will be).

Please be reminded that - even with the threadsafe MFC classes or native ODBC calls - the ODBC dirver itselfs needs to be threadsafe. This isn't the case for many single-tier drivers like dBase or MS Access. We prefer SQL server, which was specifically designed for multithreaded environments and is a sure bet.

Credits to Bill Crowell (Bill_Crowell@STERCOMM.COM) who brought this issue first to our attention.