Integrated: 8334223: Make Arena MEMFLAGs immutable

[Thomas Stuefe]

On Thu, 13 Jun 2024 11:59:05 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

> Arenas carry NMT flags. 
> 
> An arena should never change that flag. But it does: Arenas (as ResourceAreas), used by CompilerThread, are accounted toward mtCompiler. But since the RA is already created in the parent class constructor (as mtThread), we then have to awkwardly change the flag of an already existing RA in the CompilerThread constructor.
> 
> As a prerequisite for future NMT work I would like Arena MEMFLAGS to be immutable.
> 
> The patch does that:
> - we hand in MEMFLAGS to the Thread constructor now (defaults to mtThread)
> - CompilerThread hands in mtCompiler, all other threads rely on the default
> - on creation, both ResourceArea and HandleArea are now accounted toward the flag handed in
> - that allows us to make Arena::flags const, and to remove ResourceArea::bias_to which changed the flag in-flight for the arena
> - it also allows us to make Arena::flags private
> 
> Other, unrelated cleanups:
> - Made Arena::_size_in_bytes and Arena::_tag private
> - Merged both Arena constructors into one by specifying a default value of `Chunk::init_size` for `init_size` argument. That makes it equivalent to the old `Arena(flag, tag)` constructor
> - removed `JavaThread::JavaThread(bool)`. That constructor was used when creating threads that are getting attached. There was only a single use for that constructor, and I replaced it with functionally equivalent code.
> 
> Tests:
> 
> I manually verified that the NMT numbers printed don't change.

This pull request has now been integrated.

Changeset: 974dca80
Author:    Thomas Stuefe <stuefe at openjdk.org>
URL:       https://git.openjdk.org/jdk/commit/974dca80df71c5cbe492d1e8ca5cee76bcc79358
Stats:     77 lines in 12 files changed: 15 ins; 36 del; 26 mod

8334223: Make Arena MEMFLAGs immutable

Reviewed-by: jsjolen, azafari, gziemski

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PR: https://git.openjdk.org/jdk/pull/19693