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https://issues.apache.org/jira/browse/GROOVY-11775?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18038483#comment-18038483
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Björn Kautler commented on GROOVY-11775:
----------------------------------------
> I don't have a great way to test this. I pushed to my local and ran the spock
> tests. However, this was a once-in-a-while condition and the tests OOM for me
> either way.
Actually, with the root cause in mind now, 100% reproduction and testing should
be trivial:
https://groovyconsole.dev/?g=groovy_4_0&codez=eNpLzkksLlZwy89XqOZSUEhJTVMoLkksSVWwVchLLVcISsxLyc_V0NTLS60o8cwr0dDkquVKBmtxSiwCaqnlAtJ6uZkVmXkaQEM0uUAmJAGlIPqBkkAtBUWZeSU5eRpAcT2w6ViF0AwiThMAgoI_-w
[code:groovy}
class Foo {
def state = new Random().nextInt()
}
class Bar {
}
Bar.mixin(Foo)
def bar = new Bar()
println(bar.state)
println(bar.state)
Bar.mixin(Foo)
println(bar.state)
println(bar.state)
{code}
Without your fix first two print the same, last two print the same, but first
and last two print different ones.
With your fix, all four should print the same.
> Stateful runtime mixins sometimes do not work properly
> ------------------------------------------------------
>
> Key: GROOVY-11775
> URL: https://issues.apache.org/jira/browse/GROOVY-11775
> Project: Groovy
> Issue Type: Bug
> Affects Versions: 4.0.26
> Reporter: Björn Kautler
> Assignee: Eric Milles
> Priority: Major
> Attachments: StarTrekPatrickStewartGIF.gif
>
>
> I have class {{A}} and class {{B}}.
> I {{mixin}} {{A}} to {{B}} using {{B.mixin(A)}}.
> {{A}} has a property {{X}}.
> Now I have a method {{M}} in a subclass of {{B}} which first calls a method
> {{N}} of {{A}}, then another method {{O}} of {{A}}.
> Both calls happen linearly, both happen on the same thread, yet occasionally
> the call to {{O}} hits a different instance of {{A}} than the call to {{N}}
> and thus {{N}} and {{O}} work on a different instance of the field in {{A}}.
> From a quick look at the code and debug, the problem might maybe be, that the
> {{MixinInMetaClass#managedIdentityConcurrentMap}} holds the {{B}} instances
> that serve as key in soft references. So maybe if the heap gets exhausted
> between calling {{N}} and {{O}}, the map entry is nuked by the garbage
> collector and thus the {{O}} call creates a new {{A}} instance.
> If this is the case (or actually whatever else causes what I see), stateful
> runtime mixins are quite flaky and should not be used unless this is fixed,
> as you cannot rely on the state. Actually, I was not able to knit an MCVE by
> intentionally triggering two OOME between the calls to {{N}} and {{O}}, so my
> suspicion about the cause might not be correct.
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