RFR (S) 8160539: Stack frame scanning acquires several mutexes

[dean.long at oracle.com]

Is it OK to do a normal read of _oop_map_cache here:

+    if (!Atomic::replace_if_null(oop_map_cache, &_oop_map_cache)) {
+      // Some other thread won.
+      delete oop_map_cache;
+      oop_map_cache = _oop_map_cache;
      }

or does it need to be load-acquire or volatile?  We don't want the 
compiler to use the value from the earlier read:

    OopMapCache* oop_map_cache = OrderAccess::load_acquire(&_oop_map_cache);


dl

On 3/25/19 10:49 AM, coleen.phillimore at oracle.com wrote:
> Summary: Use CAS instead of OopMapCacheAlloc_lock
>
> Tested with hs-tier1-5 and specjbb2017.
>
> open webrev at http://cr.openjdk.java.net/~coleenp/2019/8160539.01/webrev
> bug link https://bugs.openjdk.java.net/browse/JDK-8160539
>
> Thanks,
> Coleen