Is there any way to disable the session locking in PHP while using the default session handler?
[EDIT:] Or is there at least a way to restart a session after callin
There is no way of disable locks from php sessions. It's a real nighmare use case of locking. Only way to get rid of sessions and/or php. As a temporary solution you may want to use riak session handler: https://github.com/zacharyfox/riak-php-sessions it's lock free, and it's working.
Last versions of memcached session handler also introduces locking for some insane reasons and no way to disable it.