RFC (round 1), JEP draft: Low-level Object layout introspection methods

Florian Weimer fw at deneb.enyo.de
Sun Aug 23 20:37:26 UTC 2020

* Aleksey Shipilev:

> I can see that the JEP can be split in "non-controversial" (sizeOf,
> deepSizeOf) and "controversial" (addressOf, fieldOffsetOf)
> parts. For the process overhead reasons, I'd push forward with just
> one JEP at the moment, though.

Are there JVMs out there where naive implementation of deepSizeOf
(with something like IdentityHashMap in the background) would itself
change object layout and sizes?

A theoretical implementation of System.identityHashCode() might
allocate a word for the identity hash only after the method has been
applied to the object and the object has been moved.

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