How to share an array?

I want to share a list of visitors of chat room with SharedObject. I was going to put and array into shared object's field. Is it possible? And also I was realized that it is impossible to synchronize shared array correctly. If two visitors will add themselves to the list simultaneously, then one can be lost.

Is it possible to synchronize access to shared object somehow or the only way is to write server side function to control the array?