Symphony doesn't natively supported pessimistic database locking, so I created an extension in symphony to handle it, both in the backend and the frontend. It's somewhat complicated to implement, but so far it works pretty great. I created it because one of the next big projects I'm working on will be used by many people at once, and I was considering using symphony to create it, as opposed to Rails.
You can get it here.
Report any issues at GitHub.