Added lock-based synchronization for _data access. Added some comments. Newly arrived data will no longer overwrite earlier data.
Added lock-based synchronization for _data access. Added some comments.
Newly arrived data will no longer overwrite earlier data.

Jumaga2015/qdms,KBurov/qdms,qusma/qdms,leo90skk/qdms,leo90skk/qdms,underwater/qdms,underwater/qdms,qusma/qdms