RFR: 8212879: Make JVMTI TagMap table not hash on oop address

[Coleen Phillimore]

On Mon, 2 Nov 2020 08:34:17 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> src/hotspot/share/prims/jvmtiTagMap.cpp line 126:
>> 
>>> 124:   // concurrent GCs. So fix it here once we have a lock or are
>>> 125:   // at a safepoint.
>>> 126:   // SetTag and GetTag should not post events!
>> 
>> I think it would be good to explain why. Otherwise, this just leaves the readers wondering why this is the case.
>
> Maybe even move this comment to the set_tag/get_tag code.

I was trying to explain why there's a boolean there but I can put this comment at both get_tag and set_tag.

  // Check if we have to processing for concurrent GCs.
  // GetTag should not post events because the JavaThread has to
  // transition to native for the callback and this cannot stop for
  // safepoints with the hashmap lock held.
  check_hashmap(false);

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

PR: https://git.openjdk.java.net/jdk/pull/967