[ http://issues.apache.org/jira/browse/JS2-457?page=all ]
David Jencks updated JS2-457:
-----------------------------
Attachment: pipeline.diff
> JetspeedPipeline synchronization is broken and using a threadlocal is really
> ugly
> ---------------------------------------------------------------------------------
>
> Key: JS2-457
> URL: http://issues.apache.org/jira/browse/JS2-457
> Project: Jetspeed 2
> Type: Bug
> Components: Container
> Reporter: David Jencks
> Attachments: pipeline.diff
>
> I previously addressed these issues in J2-115 and still think that is a
> better solution. Here is a way to remove use of a threadlocal to track a
> call's progress through the valves that does not change any classes or
> configuration other than JetspeedPipeline.
> In addition, the synchronization in JetspeedPipeline is fairly useless. Some
> problems include:
> suppose 2 calls come simultaneously and block on valves1. The first call
> changes valves to point to valves2. While the second call is changing
> valves2 to valves3, while locking valves1, a third call comes in, finds
> valves2 unlocked, and changes valves2 to vavles4. The result might be
> valves3 or valves4, but won't have both changes.
> Also, the access to valves while traversing the pipeline needs to be
> synchronized, or there is no guarantee that a completely written vavle array
> will be accessed: according to arguments made around "double checked locking
> is broken", the JIT can rearrange code so that the "valves" variable can be
> set before the array is filled in.
> I believe all the synchronization can be removed if the addValve and
> removeValve methods are eliminated. I personally think this would be a good
> idea.
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