> small problem. build an experiment, start taking data, observe how ODB is never saved to disk because the "last client" never stops. as bonus, crash 
> the computer, observe how all changes to ODB are now lost. if mlogger is configured to save odb.json at the end of run, and to write ODB dumps at 
> begin and end of every data file, you can recover some of the lost 

The new behavior is not much worse than before. Assume 10 programs running happily for days, computer crashes, all ODB changes lost. 
So indeed a periodic flush without holding the lock might be best. Use a semaphore to prevent all programs flushing at the same time, or put
the flush only in the logger after an end of run.

Stefan