RFR: 8290041: ModuleDescriptor.hashCode is inconsistent

[Alan Bateman]

On Sat, 6 Aug 2022 08:08:43 GMT, Jaikiran Pai <jpai at openjdk.org> wrote:

> Can I please get a review of this change which proposes to fix https://bugs.openjdk.org/browse/JDK-8290041? 
> 
> As noted by the reporter, the current implementation is buggy since the calculation can result in a different value of the hashcode depending on the order of iteration of the `Modifier`s. The commit in this PR changes that computation to produce consistent result irrespective of the order in which the `Modifier`s (enum) is iterated upon.
> 
> A new test has been added which reproduces the issue and verifies the fix.

> Sorry for joining late. I noticed that modsHashCode is a private method and it takes Iterable> as a parameter. But everywhere it is called, a Set> is passed to it. So why not just calling the set.hashCode() and be done with it? It may be even more optimal in some cases.

There's a lot going on here as the hash code is generated at link time and we also want it to be reproducible across builds. We also had a CDS bug with the  the way that Enum objects were archived - Ioi has fixed that in JDK 19 so we have one less thing to be concerned about now.

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PR: https://git.openjdk.org/jdk/pull/9790