[wildfly-dev] Discarding the changed management model during operation rollback

[James R. Perkins]

Not much more I can say than +1.

I can't think of a good reason why an OSH would need to know anything 
about the failed model update on a rollback.

On 07/01/2015 09:43 AM, Brian Stansberry wrote:
> tl;dr;
>
> When an operation that has changed the management model is rolling back,
> the OperationStepHandlers processing the rollback see the model as it
> was at the arbitrary point when the rollback began. I propose changing
> this so they see things as they were prior to the first change to the model.
>
> Long version:
>
> When an operation mutates either the management Resource tree, or the
> registry of capabilities (together known as the management model), we
> clone the management model and thereafter that operation works on the
> clone. The clone is invisible to other callers until the operations
> successfully commits. When the operation commits, it publishes the clone
> and that becomes the official model.
>
> I call this copy-on-write, publish-on-commit.
>
> If the operation rolls back, the changed model is never published and
> the clone is just discarded when the operation execution returns.
>
> However, while the operation is rolling back, all the
> OperationStepHandlers that are processing the rollback see the modified
> clone, not the original model. They are seeing arbitrarily incorrect data.
>
> This hasn't been a problem up to now, as our standard OSHs get a copy of
> whatever part of the Resource tree they are going to modify and keep it
> for use in rollback. They don't need to re-read the management model to
> perform rollback.
>
> But this doesn't work for the capability registry. If an OSH removes a
> capability and removes a service, and then in rollback tries to use the
> capability to figure out how to restore the service, it fails, as
> management model it can see still shows the capability as being removed.
>
> To fix this, I propose discarding the cloned management model as soon as
> rollback begins. Thereafter, an OSH processing rollback will see the
> model as it was before the first modification. The removed capability
> will still be present.
>
> I have a commit that does this at [1]. Running the testsuite with it
> shows no regressions. This doesn't surprise me, as our standard OSHs up
> to now have had no need to re-read the model during rollback.
>
> [1]
> https://github.com/bstansberry/wildfly-core/commit/419f350931d5b7e345cf9aa514de08c01bf976be
>

-- 
James R. Perkins
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