#20 [BUG] Serialized Pids and Refs can cause crash after a restart

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#20 ✓resolved

[BUG] Serialized Pids and Refs can cause crash after a restart

Reported by Rusty Klophaus | January 4th, 2009 @ 09:17 AM

Found by Dave Peticolas.

After a restart, a user may hit the site with a session cookie from an old run. Nitrogen will attempt to verify the session, and in the process send a {Pid, verify, Ref} message to the Pid.

If the Pid is now running some other process, it can choke on the message, potentially crashing the system.

This arises because Pids and Refs are re-used.

To solve, either:

1) Don't use a Pid to look up a session, use a Guid instead, and then have a Guid -> Pid lookup table. Potential bottlenecks here.

2) Find some way to check if the Pid is valid before sending a message to the Pid. One possibility is to generate a unique value each time Nitrogen starts up, serialize this in the session cookie, and then check to make sure that the two match. This presents challenges when we run more than one Nitrogen instance.

Comments and changes to this ticket

You flagged this item as spam.
Joshua January 4th, 2009 @ 12:50 PM
The second way seems far more intelligent than the first. It would be trivial to share a per-run unique value that is shared across instances.

I haven't checked out the nitrogen code base deeply yet, let me know if I'm wrong.
Rusty Klophaus January 6th, 2009 @ 09:36 PM
(from [459ed83a703e27d16119c173bf0ce8f2e47ea0e1]) Turn Nitrogen into a supervised application. Apply changes by Dave Peticolas to turn session state into a supervised process. [#20 status:resolved] http://github.com/rklophaus/nitr...
Rusty Klophaus January 6th, 2009 @ 09:42 PM
- State changed from “new” to “resolved”

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