[infinispan-dev] Fix or document? Concurrent replaceWithVersion w/ same value might all return true - ISPN-4972

[Radim Vansa]

I agree with Galder, fixing it is not worth the cost.

Actually, there are often bugs that I'd call rather 'quirks', not 
honoring the ConcurrentMap contract (recently we have discussed with Dan 
[1] and [2]) which are quite complex to fix. Another one that's 
considered not a bug is that a read does not have transactional semantics.
Galder, where will you document that? I think that special page in 
documentation should accumulate such cases, linked to JIRAs for case 
that eventually we'll resolve them (with that glorious MVCC). And of 
course, link from javadoc to this document (though I am not sure whether 
we can correctly keep that in sync with latest release. Could we have a 
redirection from http://infinispan.org/docs/latest to 
http://infinispan.org/docs/7.0.x/ ?

Radim

[1] https://issues.jboss.org/browse/ISPN-3918
[2] https://issues.jboss.org/browse/ISPN-4286

On 11/13/2014 01:51 PM, Galder Zamarreño wrote:
> Hi all,
>
> Re: https://issues.jboss.org/browse/ISPN-4972
>
> Embedded cache provides atomicity of a replace() call passing in the previous value. This limitation might be lifted when we adopt Java 8 and we can pass in a lambda or similar, which can be executed right when the value is compared now, and if it returns true it’s applied. The lambda could compare both value and metadata for example.
>
> Anyway, given the current status, I’m considering whether it’s worth fixing this particular issue. Fixing the issue would require adding some kind of locking in the Hot Rod server so that the version retrieval, comparison and replace call, can all happen atomically.
>
> This is not ideal, and on top of that, as Radim said, the chances of this happening in real life are limited, or more precisely it’s effects are minimal. In other words, if two concurrent threads call replace with the same value, the end result is that the new value would be stored, but as a result of the code, both replaces would return true which is not strictly right.
>
> I’d rather document this than add unnecessary locking in the Hot Rod server where it deals with the versioned replace call.
>
> Thoughts?
> --
> Galder Zamarreño
> galder at redhat.com
> twitter.com/galderz
>
>
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-- 
Radim Vansa <rvansa at redhat.com>
JBoss DataGrid QA