not possible to call CI controllers simultaneously?

[eluser]Jim OHalloran[/eluser]
Instead pof PHP's native session handling you might want to try CI's in-built session library. It doesn't use the PHP session functionality, and may not suffer from this problem.

This post on the "Thwarted Efforts" blog deals with PHP Sessions and race conditions, and seems to describe a problem similar to what you're experiencing. It provides a solution that allows you to lock only a single value in the session which might be of benefit to your situation.