Sync Advise Android Devices

[Paolino Angeletti]

Hi guys,
i'm developing a syncronization between two databases, one in local in SQLLite and one on Cloud.
The problems that i want to solve is this:
i want that max one device can sync their datas, and i would implement it in mutex-style, example:

device 1 -> request sync permission -> ok, sync -> block sync
device 2 -> request permission -> wait device 1
device 3 -> request -> wait dev 2
dev 1 .complete sync
start dev 2
start dev 3

how can i implement this situation ??
thanks