Race Conditions with Ajax and PHP Sessions

One of the problem with race conditions is that it is often difficult to actually witness the ramifications of one when it happens, especially if you are not aware of it. If you’ve used PHP’s built-in, default session handling (that uses files), you’ll never come across the problem. However, things get interesting once you start using session_set_save_handler to write your own session handler.
Quelle:

• Race Conditions with Ajax and PHP Sessions
• Parallel Request mit AJAX und PHP
• Troubles with Asynchronous Ajax Requests and PHP Sessions