General callback for threaded SQL stuff.
typedef SQLTCallback = function void(Handle owner, Handle hndl, const char error, any data)
Parent object of the Handle (or INVALID_HANDLE if none).
Handle to the child object (or INVALID_HANDLE if none).
Error string if there was an error. The error could be empty even if an error condition exists, so it is important to check the actual Handle value instead.
Data passed in via the original threaded invocation.