File Locking In samba , So Help me To implementation
 

I have one folder /repo , it contain txt file , i want to share this files between two user A and B using SAMBA , Both USer Have Read And Write permission , I want when user A open this file and trying some modification ,same time user B trying to Open same file but he will not able to open ,and not able to change , when User A done his Job then User B able to MOdify and access this file