When you use ActiveX Data Objects (ADO) and set the
CursorLocation property for
Connection or
Recordset to
adUseClient, and specify asynchronous fetching with
adAsyncFetch and
adAsyncFetchNonBlocking for the execution options of the
Execute or
Open method, the client cursor engine creates a background thread to fetch data from the OLE DB Provider. With a custom provider, you may see the data fetched synchronously (the call to
Execute or
Open doesn't return until all of the data has been fetched).
Because the cursor engine fetches from the provider on different threads in the asynchronous case, the provider is required to return DBPROPVAL_RT_FREETHREAD for the rowset property DBPROP_ROWTHREADMODEL.
To allow the background fetching, a provider must return DBPROPVAL_RT_FREETHREAD for the rowset property DBPROP_ROWTHREADMODEL. This is necessary because the cursor engine is creating a secondary thread, which will continue fetching the data from the underlying rowset. The cursor engine is ensuring that apartment model rules are not being broken.
The behavior is by design.
