Session locking problems?

[temp]

Try this, on a vanilla symfony-2.2.0

Edit src/Acme/DemoBundle/Controller/SecuredController.php, add sleep(100); to the helloAction.

In your browser, open symfony, access the secured area of the Acme Demo, login as admin.

Open /demo/secured/hello/World, it should load a long time because of the sleep().
Open /demo/secured/hello/admin/World in a second tab.

Now you will see that the second tab will return its response only AFTER the sleep() of the first tab is finished.

Why is this so? Does it happen because of session locking? Or is it a bug?

[temp]

This happens in prod and dev, and only for secured pages.

[mpdude]

This happens because PHP does session locking. If you have one request with an open PHP session, all other requests for the same session will block in session_start() until the first request finished. More precisely, all requests for that session will be executed one after another.

This is necessary to avoid race conditions - assume both requests were handled in parallel and modified values stored in the session, then PHP would have to bring a merge strategy (which it can't for the general case) or the "last one wins" which is probably not what you want either.

You might want to experiment with session_write_close() or google for "php session concurrency" or the like.

Probably not a Symfony bug, though.

[vicb]

This is indeed the expected behavior as @mpdude mention.

Requests which result in accessing the "Symfony session" are serialized because of the PHP session lock.

You should note however that there is a bug in Symfony for non native storage which do not use a lock, see #4976.