Implementation of Google docs - how to organize access to one file at a time for writing?

Question

Google

It would be desirable to learn as it is possible to implement simultaneous record in a file, pieces of a file.
Google Docs implements file sharing, I want to implement the same.
Help, where to dig?

Answer 1

file sharing

not to a file but to a document. These are slightly different things.
Smoke towards websockets.

Answer 2

If I remember correctly, both OpenOffice and the new MSOffice support shared document access.
Implementation details are in their documentation.
If you need your own bike, there is a lot of things besides websockets )
It's worth looking in the direction of some kind of message queue, such as rabbitmq.