Multi request scheduling

I have a photon where I have setup a data to publish and a command to execute.
I have written a web client that runs GET every 30 secs and run POST on user click.
GET and POST are asynchronous
On the photon side, there is infinite LOOP that does nothing except updating the data published every 15 secs by requesting them from an Arduino (it can takes few secs)

I would like to understand how the photon replies to the GET and the POST. When the GET of the POST, I suppose that there is an interrupt mechanism to ask to the the photon to provide the content of the data or to run command requested.

Is this interrupt always enable ? it seems that sometimes the web client issue a POST and then an GET but it receives first the answer of the GET and then the answer of the POST.

Is there a way to control the sequence ?

Thanks to explain more deeply the behavior of the photon