[5.3] Fix empty session

[lcharette]

Fix session being empty when the file is being read and/or written by multiple instance of apache simultaneously. This append to me when assets (javascript / css) are being loaded dynamically using php. Multiples assets in the same request cause the sessions to be corrupted.

[taylorotwell]

@GrahamCampbell @themsaid do you know of any problems with this?

[maki10]

Hey @taylorotwell I have the same issue when using multiple iframe elements. If a session is not in Redis, a session will be random expired.

I can reproduce this issue with my Admin panel that is built for Laravel on a fresh install of Laravel.

[GrahamCampbell]

do you know of any problems with this?

Looks ok. I guess it doesn't matter that much, since any real usage will be using apc or redis, or the like.

[lcharette]

From all the debug and tests I did, the error I encounter was really when the same session file was read/write more than once in a very very short time period (simultaneously). It would randomly return noting. Probably something related to file_get_contents trying to read the file while it's being written.

As seen here, adding the lock option to true force php to get a read lock on the file before reading it's content, assuring the file will indeed be read.

[taylorotwell]

So adding this change fixed your original problem in your tests?

[lcharette]

Yes. Like I said, this force php to get a read lock on the file before reading it's content, assuring the file will indeed be read correctly. So the file read won't return en empty string as the session data, forcing a new session to be created by our system.

[frohlfing]

it seems to fix my issue #15551, too!

[lcharette]

What you describe in #15551 is similar to the problem I had, so good chances this indeed fixed your error too ;)