RFR: 8356173: Remove ThreadCritical [v2]

[Kim Barrett]

On Fri, 9 May 2025 16:53:11 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> @coleenp But surely one can statically allocate a pthread_mutex_t and assign PTHREAD_MUTEX_INITIALIZER, no? I mean that's Unix 101. MacOS should be able to do that at least.
>> 
>> Looking at PlatformMutex, maybe it is not the right tool for the job. One needs a simple stupid mutex class like this:
>> 
>> 
>> struct SimpleMutex {
>>     pthread_mutex_t _m;
>>     SimpleMutex() : _m(PTHREAD_MUTEX_INITIALIZER) {}
>>     lock() -> do pthread_mutex_lock
>>     unlock() -> do pthread_mutex_unlock
>> };
>> static SimpleMutex mymutex;
>> 
>> 
>> etc.
>
> Note that such a simple solution would also reduce the number of indirections when using this mutex. One less pointer load, one less memory access.

@tstuefe We can't rely on PlatformMutex being initialized that way, because the Windows implementation
requires a _call_ to `InitializeCriticalSection`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25072#discussion_r2082444850