[ABDERA-294] server RouteManager threading: MapCtx parameters cleared and replaced with empty parameters

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 1.1.2
• Fix Version/s: 1.2
• Environment: Abdera 1.1.2
• Assignee: Unassigned
• Reporter: Bob Fields
• Created: 19/Jan/12 19:31
• Updated: 28/Sep/13 14:55

Description

The hrefParams map is cleared and then subsequent requests not properly routed. Our problem doesn't occur on load, but rather occurs sometime after when two requests hit cleanMapCtx in the right timing to have one clear out the map as the other is grabbing the entry set, resulting in the second thread doing a clear but having nothing to put back in. Then all subsequent requests don't get routed properly.

This is similar to https://issues.apache.org/jira/browse/ABDERA-95 and https://issues.apache.org/jira/browse/ABDERA-276 but does not occur under load, just with two threads.

In the comments for that issue, there's a mention of a fix by using the code from an earlier version. I haven't tested the code mentioned from 0.4.0, but from looking at it the hrefParams isn't being modified, so that would seem to solve our problem as well. I'm attaching the diff for the fix that we used, which was to return the new map instance with the cleaned keys instead of altering and returning the hrefParams.

The problem we experienced was that the ATOM feed would intitally be working, but then would start returning 404 errors. We found that this was caused by the hrefParams property of the AtomCollectionAdapter being corrupted (cleared out) by the cleanMapCtx method in RouteManager. This occured when mutliple threads hit RouteManager.cleanMapCtx in close succession, such that the first thread cleans the shared map as the second is trying to iterate over the entries in the map. The second thread will then clear the map, but have nothing to put back in it, resulting in the map being empty for all future requests.

We ran into this fairly often in testing with a decent load, but the easiest way to recreate this on demand is to debug remotely and manually step through two threads so that they hit at the right time. I've included the steps I used below.

Steps to re-create by remote debugging:
Set breakpoint in RouteManager.cleanMapCtx line 176
In thread 1, step through to after the map has been cleared (line 181)
In thread 2, step through to line 180. This thread will now have an empty map, since it got the entrySet after the first map was cleared, but before the putAll
Play thread 1
Play thread 2
The map will be null for all future threads

Issue Links

• relates to: ABDERA-276 DefaultProvider doesn't properly handle parameters in base routes