On Wed, 25 Nov 2020 18:40:49 GMT, Coleen Phillimore <cole...@openjdk.org> wrote:
> The ServiceThread cleaning used a stale ObjectFree state when calling
> remove_dead_entries, because another thread had concurrently set is_enabled
> to false. Add a lock around setting/resetting the lock event state and
> retest the state under a lock. Ran the test 100s of time without failure,
> where otherwise it fails very quickly.
> Tested with tier2,3 and running tiers 4,5,6 in progress.
> Thanks to Kim for his previous feedback.
Marked as reviewed by kbarrett (Reviewer).
src/hotspot/share/prims/jvmtiEventController.cpp line 463:
> 461: ((now_enabled & OBJECT_FREE_BIT)) != 0) {
> 462: // Set/reset the event enabled under the tagmap lock.
> 463: set_enabled_events_with_lock(env, now_enabled);
You could tighten up the test to only handle specially when the state of the
ObjectFree event is changing, i.e.
(((was_enabled ^ now_enabled) & OBJECT_FREE_BIT) != 0)```
Or you could not bother with the conditionalization at all, and just always
call set_enabled_events_with_lock; I bet nobody would notice any performance
difference. That would eliminate "benign" races between unlocked bit setting
here and bit testing in remove_dead_entries_locked. Of course, the current
implementation has such races on these bits all over the place; what's one race
more or less among friends...
Or you could just leave it as you have it. Your call.
-------------
PR: https://git.openjdk.java.net/jdk/pull/1439
