Samba provides all the same locking semantics that MS Windows clients expect and that MS Windows NT4/200x servers also provide.
The term locking has exceptionally broad meaning and covers a range of functions that are all categorized under this one term.
Opportunistic locking is a desirable feature when it can enhance the perceived performance of applications on a networked client. However, the opportunistic locking protocol is not robust and, therefore, can encounter problems when invoked beyond a simplistic configuration or on extended slow or faulty networks. In these cases, operating system management of opportunistic locking and/or recovering from repetitive errors can offset the perceived performance advantage that it is intended to provide.
The MS Windows network administrator needs to be aware that file and record locking semantics (behavior) can be controlled either in Samba or by way of registry settings on the MS Windows client.