Finalizer being run while class still in use (escape analysis bug)

[Andrew Haley]

On 10/10/2018 02:09 PM, Erik Österlund wrote:
> The implementation of reachabilityFence was changed recently to become a 
> normal static method, and stop forcing no inlining. No magic and special 
> treatment by HotSpot.

I'm sure it depends on the JIT being used. I'm slightly surprised
something so simple works, given that a normal empty method could be
trivially inlined and the reference dropped. And we know that does
happen, so I wonder why not here?

Incidentally, I can't find the review thread for 8199462.

> I think the analysis made was that the oops would have to be kept
> alive based on the bytecode level live analysis, as required by
> deoptimization to work as expected.

> I was curious if this works with Graal and asked Graal folks about it. 
> Turns out it works the same for Graal as JIT and AoT, due to the need to 
> support deoptimization in those configurations, leading the oops to be 
> kept alive. But with SVM, an actual intrinsic will be added to support 
> this operation, as there is no need for deoptimization in SVM, causing 
> the compiler to go a bit further.

Mm, yes. It's not at all nice that the correctness of the Java library
relies on something which seems to be a side effect of the design of
the JIT. Still, it's up to other JITs to provide their own
implementation.

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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