RFR: 8308603: Removing do_pending_ref/enclosing_ref from MetaspaceClosure

[Coleen Phillimore]

On Tue, 23 May 2023 01:47:18 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> **The problem**
> 
> MetaspaceClosure is used to traverse all *pointers* in the metaspace objects. It works recursively. A pointer is represented by the `MetaspaceClosure::Ref` type. For example, if you have
> 
> 
> InstanceKlass* a = ..., *b = ...;
> a->_super = b;
> 
> 
> When we are traversing the pointer `a->_super`, we create a `Ref` that records the address of `b` and `&a->super`. However, we currently don't remember the address of `a` in the `Ref`. As a result, when processing the `Ref` inside a `push(Ref* ref)` function, we need to call `MetaspaceClosure::enclousing_ref()` to get to `a`, so that we can mark pointers inside it.
> 
> The reason for`do_pending_ref` is even more convoluted. Please see [JDK-8308603](https://bugs.openjdk.org/browse/JDK-8308603) for more details.
> 
> **The fix**
> 
> The code can be much more readable if we simply remember  `a` in the `Ref`.

src/hotspot/share/cds/archiveBuilder.cpp line 452:

> 450: 
> 451:   // We are dealing with 3 addresses:
> 452:   // address o    = ref->obj(): We have found an object whose address is o.

Are 'obj' oops ?  We almost always refer to oops as obj but not other things.  Is 'object' an oop?  This operates on metadata right? I realize this terminology is pre-existing.  I suggest changing obj and object in comments at least in the new code to either metadata() or ptr() even, metaptr() ?   Unless this does move oops. I don't know this code.

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PR Review Comment: https://git.openjdk.org/jdk/pull/14093#discussion_r1202160387