RFR: 8304824: NMT should not use ThreadCritical [v8]

[Johan Sjölen]

On Wed, 2 Oct 2024 13:28:13 GMT, Robert Toyonaga <duke at openjdk.org> wrote:

>> ### Summary
>> This PR just replaces `ThreadCritical` with a lock specific to NMT.  `ThreadCritical` is a big lock and is unnecessary for the purposes of NMT. I've implemented the new lock with a semaphore so that it can be used early before VM init.  There is also the possibility of adding assertions in places we expect NMT to have synchronization. I haven't added assertions yet in many places because some code paths such as the (NMT tests)  don't lock yet. I think it makes sense to close any gaps in locking in another PR in which I can also add more assertions. 
>> 
>> Testing:
>> - hotspot_nmt
>> - gtest:VirtualSpace
>> - tier1
>
> Robert Toyonaga has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Update src/hotspot/share/utilities/vmError.cpp
>   
>   Co-authored-by: David Holmes <62092539+dholmes-ora at users.noreply.github.com>

Hi,

Big thanks to David for taking the heavy brunt of reviewing this change. This code looks good to me, it's a bit unfortunate that we have to export `MemTracker::reduce_tracking_to_summary` for the limited use case of exiting the VM on error, but OK. Let's wait for Thomas to come back for this change, I think it's not more than fair that he gets to have another look at this.

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Marked as reviewed by jsjolen (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20852#pullrequestreview-2356793662