Please critique: solution to database connection and multiple threads

[yeye_olive]

This is coming a bit late, especially since you have moved away from your one-connection-per-thread solution, but if you ever have to do something like that again, consider using thread-local storage (see QThreadStorage for Qt's implementation) instead of rolling out your own map protected by a mutex. Thread-local storage is supported by the C11 and C++11 standards, and is usually natively supported by the OS. IIRC a typical implementation consists in reserving a CPU register that points to a different memory area for each thread.