Are cookie read/write atomic in browser

Question

I am trying to implement a cross tab mutex for my needs. I found a implementation here. which seems quite promising. Basically, it implements Leslie Lamport's algorithm with needs atomic read/writes for creating a mutex.

However it relies on localStorage providing atomic read/writes. This works well in most browsers except for Chrome.

So my question is, can I use cookie read/write instead? Are cookie reads/writes atomic in all mainstream browsers (IE, Chrome, Safari, Firefox)?

Answer 1

Neither cookies, nor localStorage provide atomic transactions.

I think you might have misunderstood that blog post, it doesn't say that his implementation doesn't work in Chrome, it does not rely on localStorage providing atomic read/writes. He says that normal localStorage access is more volatile in Chrome. I'm assuming this is related to the fact that Chrome uses a separate process for each tab, whereas most other browsers tend to use a single process for all tabs. His code implements a locking system on top of localStorage which should protect against things getting overwritten.

Another solution would be to use IndexedDB. IndexedDB does provide atomic transactions. Being a new standard it is not supported in as many browsers as localStorage, but it does have good support in recent versions of Firefox, Chrome and IE10.