sync LC applications

[paolo mazza]

Hi all,
what’s the best way to sync several  LC applications installed on many different devices?
For example, consider having 100 smartphones connected to internet running the same LC application, how can I send a signal/command so that an image shows up  at the same time in every smatphone?
AFAIK a solution is to set up a text file in a web server and let the app installed in each device to check (every second)  if any change occour , but this solution is not efficient.
Any idea?
Best regards,
Paolo Mazza