RFR: 8356173: Remove ThreadCritical

[Coleen Phillimore]

On Fri, 9 May 2025 13:20:06 GMT, Zhengyu Gu <zgu at openjdk.org> wrote:

>> Updated the description in the bug.  This removes the last use of ThreadCritical and replaces it with a global PlatformMutex lock.
>> Tested with tier1-4, and tier1 on all Oracle-supported OSs.
>
> src/hotspot/share/nmt/mallocTracker.cpp line 68:
> 
>> 66:   // copy is going on, because their size is adjusted using this
>> 67:   // buffer in make_adjustment().
>> 68:   ChunkPoolLocker lock;
> 
> At the time NMT was written, `ThreadCritical` was the only native lock. I wonder it is the time NMT gets its own lock?

Yes, ThreadCritical preceded the PlatformMutex locks, which were added later.  We had ThreadCritical (iirc) for a limitation in the Windows malloc code, which is why it was around all the os::malloc calls once. NMT just built upon that since it was there.
We cannot use regular Mutex because Mutex requires Thread::current() which doesn't exist at this point. The NMT code might be able to use a lock around the code that deletes arenas, as the comments suggest that it is trying to protect.  This could be a regular Mutex because the arena code is deleted individually and purged well after startup time.  I left this as a shared lock, but it could be further improved to use a nmt-delete-lock Mutex.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/25072#discussion_r2081860936