Multithreading: got code SQL_INVALID_HANDLE when SQLGetData called

As the title suggests, I encountered the SQL_INVALID_HANDLE error from SQLGetData function. It appears that the Driver::call function is not thread safe.

To address this issue, I attempted to add a return code in order to obtain the error code -99:

In my program, multiple threads call ODBC functions simultaneously. Therefore, I suspect that when one thread is executing SQLGetData, and another thread is creating a new session, the 'descendants' variable is not protected by thread safety measures.

Start by inspecting the Driver::call function and how the descendants variable is accessed during SQLGetData and new-session creation. Reproduce concurrent ODBC calls from multiple threads, then verify that simultaneous SQLGetData and session creation no longer produce SQL_INVALID_HANDLE or error code -99.

Written by the indexing model from the issue text.