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

Answer 1

No. Even if the browsers probably implement a read and a write lock on the cookie it won't protect you from changes that happens between a read and a consequent write. This is easy to see by looking at the javascript API for cookies, there is no mutex functionality there...