RFR (S) 8074355: make MutexLocker smarter about non-JavaThreads

[coleen.phillimore at oracle.com]

Kim and I had a discussion about this, so I'm withdrawing this change.
Coleen

On 3/22/19 12:32 PM, coleen.phillimore at oracle.com wrote:
> Summary: Use safepoint_check_always/safepoint_check_never instead of 
> safepoint_check_sometimes for locks that are taken by JavaThreads and 
> non-JavaThreads
>
> This is a small cleanup to avoid having safepoint_check_sometimes. 
> Threads_lock is the only one remaining.  'Sometimes' was used for some 
> locks because they were taken out by GC or other threads and 
> JavaThreads, where the other threads weren't going to check for the 
> safepoint anyway since they don't participate in the safepoint 
> protocol.  There could be further cleanups here.  We could make the 
> safepoint checking related to the rank of the lock in the future, or 
> the safepoint checking could be a property of the lock so we don't 
> have to pass in Mutex::_no_safepoint_check_flag (except 
> Threads_lock).  I think these could be further enhancements after this.
>
> Tested with hs-tier1-6, runThese jck with G1, CMS, Serial and ParallelGC.
>
> 8074355: make MutexLocker smarter about non-JavaThreads
> open webrev at http://cr.openjdk.java.net/~coleenp/2019/8074355.01/webrev
>
> Thanks,
> Coleen