How does a publication onStop callback work in Meteor? - meteor

Question

Following the Meteor documentation, the onStop() function do:
Registers a callback function to run when the subscription is stopped.
Right now, I try to keep track of a user leaving a page using this onStop() function within my publication.
I expected it to work directly since the subscription is called in the template route controller and my published collection isn't available once the page is left. But I am here because even if the publication is no longer active on client, the onStop() isn't triggered. I am not sure to understand how it works, so here are the questions:
Is a publication onStop() triggered if the user leave the route it is attached to?
If not, is there a built-in Meteor mechanism to stop unused pub/subs? If yes, how does it work? Is it a timeout?
Is it necessary to use a Cursor.observe() or a Cursor.observeChanges() to use/trigger the onStop() callback?
Why is the onStop() callback not triggered when I close the browser or the tab, or logout from my current user account?

Answer 1

I discovered that it didn't trigger the onStop() because I had to move my publication query after the onStop() (since the query is behind a return).
However, since my questions might interested some people, here are the answers:
Is a publication onStop() triggered if the user leave the route it is attached to?
Yes. It stays true whether the user goes to another route of the website, close his browser tab or runs out of battery.
Is it necessary to use a Cursor.observe() or a
Cursor.observeChanges() to use/trigger the onStop() callback?
No
Why is the onStop() callback not triggered when I close the browser or
the tab, or logout from my current user account?
The fact is that is is triggered in all these cases. Here is how could look a basic publication with onStop() that I use to handle uploaded files deletion when the user does not fill up the related form and leave the page without submitting:
Meteor.publish("files", function(sessionId) {
var self = this;
// Here I clean all the files I need to remove because the user has
// not submitted the current form.
self.onStop(function () {
console.log (sessionId + " is cleaning...");
cleanFiles(sessionId)
});
// I look for files related to the current upload session only
if(Users.isInRoles(this.userId, ["user"])) {
return Files.find({"session_id":sessionId, "owner":this.userId}, {});
}
//and I make my publication available in case the if failed
return self.ready();
});