RFR: 8256830: misc tests failed with "assert(env->is_enabled(JVMTI_EVENT_OBJECT_FREE)) failed: checking"

[Coleen Phillimore]

On Fri, 27 Nov 2020 02:26:44 GMT, David Holmes <dholmes at 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.
>
> src/hotspot/share/prims/jvmtiTagMap.cpp line 1162:
> 
>> 1160:   if (_needs_cleaning) {
>> 1161:     // Recheck whether to post object free events under the lock.
>> 1162:     post_object_free = post_object_free && env()->is_enabled(JVMTI_EVENT_OBJECT_FREE);
> 
> Where is `is_enabled` called without the lock being held in a caller of `remove_dead_entries()`?

void JvmtiTagMap::flush_object_free_events() {
  assert_not_at_safepoint();
  if (env()->is_enabled(JVMTI_EVENT_OBJECT_FREE)) {

Called by JVMTI to disable events and called by the service thread.  And here for get_objects_with_tags:

  if (collector.some_dead_found() && env()->is_enabled(JVMTI_EVENT_OBJECT_FREE)) {
    post_dead_objects_on_vm_thread();
  }

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PR: https://git.openjdk.java.net/jdk/pull/1439