SAMPLE: Asynchronous MFC ODBC Database Processing Using Threads

• The Microsoft Foundation Classes (MFC) included with: - Microsoft Visual C++, 32-bit Editions, versions 4.2, 5.0

SUMMARY

This sample shows how to provide asynchronous database processing by running a database query on a secondary thread.

The following self-extracting file is available for download from the Microsoft Software Library:

 ~ Mtdb.exe (size: 38179 bytes) 

For more information about downloading files from the Microsoft Software Library, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q119591
   TITLE     : How to Obtain Microsoft Support Files from Online Services

MORE INFORMATION

Beginning with version 4.2 of the MFC database classes, the ability to set the processing mode to asynchronous using CDatabase::SetSynchronousMode() has become obsolete. The MFC ODBC classes now use only synchronous processing.

The following functions, which were used with asynchronous processing in versions before 4.2, are also obsolete: CDatabase::InWaitForDataSource(), CDatabase::OnWaitForDataSource() and CRecordset::OnWaitForDataSource().

One way to implement asynchronous database processing with MFC 4.2 and above is to run your database query on a secondary worker thread. The MTDB sample illustrates this by having each document open the corresponding recordset on a new worker thread. When the user presses the "Cancel Query" button, the primary thread cancels processing on the secondary thread.

As with any multi-threaded database application, each component must be thread-safe. Specifically, you must be using a thread-safe ODBC driver, such as the Microsoft SQL Server ODBC driver, for this application to work correctly.