RFR: 8250989: Consolidate buffer allocation code for CDS static/dynamic dumping [v2]

[Ioi Lam]

On Fri, 5 Feb 2021 23:21:14 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> src/hotspot/share/memory/archiveBuilder.hpp line 208:
>> 
>>> 206: 
>>> 207:   // For global access.
>>> 208:   static ArchiveBuilder* _current;
>> 
>> This is kind of a strange concept since ArchiveBuilder is a StackObj.  Maybe it should just be static if only one thread uses it at a time?
>
> And can a different thread call current() ? yikes.

ArchiveBuilder has temporarily allocated objects such as `ArchiveBuilder::_ptrmap`. These are easily freed when the ArchiveBuilder falls out of scope. For example, in `DynamicArchive::dump()`.

`current()` should be callable only inside the VM thread, where the dumping operations take place. I'll add an assert for that.

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PR: https://git.openjdk.java.net/jdk/pull/2296