Detect if two browser windows are open to the same site

Question

I'm trying to detect if user has my website open in one tab, then opens it in another tab. This should then show a warning to the user on the newly opened tab.

Right now I'm sending a "keep alive" ajax call every second back to the server. This then logs the "last active" time in the database with a unique ID. When a new page is loaded it checks if that user (identified by a userID) was active within the last 2 seconds.

This feels very inefficient. It also doesn't perform well when the user refreshes the page. (which takes less than 2 seconds). I've made the 2 second check longer than the keepalive call to allow for slower connections.

Q) Am I going about this the right way or is there an easier way of doing this? I heard Gmail and Facebook might do something similar but I can't find the site function in which they do it.


Actual code uses lots of in-house functions so here's the general idea:

Pseudo code:

Page load;
[index] PHP: Save tabsessionid, userid, datecreated, lastactive, phpsessionid into database;
[index] JS: Every second, send tabsessionid to keepalive.php
[keepalive] PHP: Check if another session exists in the last 2 seconds
[keepalive] PHP:        If exists -> Return "-1"; else -> return "1";
[keepalive] PHP: Update tabsessionid's last active time.

I've tried some of the solutions here but warning the newer tab, not the older one seems to be the tricky part in terms of keeping down latency/time.

Answer 1

This is just an idea you have to work on:

javascript variables are local to the tab, cookies are common. You can give each tab an id and pass it around in links and forms*. This id would be stored in a cookie as the active tab id. if a tab finds it does not have and id set, and there's active tab id set, it can use another cookie to ask if there's still such tab with this id, or was closed (and sure, it has to regulary check for this "ask" cookie and answer). Exact implementation depends on what you want to do.

I hope I explained myself clear.

EDIT:

*There's window.name js property, you can use it as window id, and you don't need to pass it around.

Answer 2

You should keep version of the content, initially at 1, with each submited edit it increases. Submited edits must include version number, which is compared to the current one and the edit is refused if they don't match. It's also possible to make ajax calls to ask for the current version, and warn the user his version is outdated.

The sql update should look like this:

UPDATE table SET .... WHERE id = :id AND version = :version

Then check affected rows, if it's 0, there was a concurent update. This way you won't encounter race condition.

Answer 3

I think u should send data (maybe simple HEAD request) to server from every window with param, contains user uid and window id(random generated once on page load), and check if exists same uid with multiple window id;

Seem this is only way.

Answer 4

Shall I say that it is inappropriate solution to whatever your problem is?

Even if you find a dirty-workaround to prevent people from multi-tabbing on your site, you will not beat the incognito mode. If you do, please do a favour and file the bug report for that browser.