This is a fix of a performance/scalability related issue. The
`JvmtiThreadState` objects for virtual thread filtered events enabled globally
are created eagerly because it is needed when the `interp_only_mode` is
enabled. Otherwise, some events which are generated in `interp_only_mode` from
the debugging version of interpreter chunks can be missed.
However, it has to be okay to avoid eager creation of these object if no
`interp_only_mode` has ever been requested.
It seems to be an extremely important optimization to create JvmtiThreadState
objects lazily in such cases.
It is done by introducing the flag `JvmtiThreadState::_seen_interp_only_mode`
which indicates when the `JvmtiThreadState` objects have to be created eagerly.
Additionally, the fix includes the following related changes:
- Use condition double checking idiom for `MutexLocker
mu(JvmtiThreadState_lock)` in the function
`JvmtiVTMSTransitionDisabler::VTMS_mount_end` which is on a
performance-critical path and looks like this:
JvmtiThreadState* state = thread->jvmti_thread_state();
if (state != nullptr && state->is_pending_interp_only_mode()) {
MutexLocker mu(JvmtiThreadState_lock);
state = thread->jvmti_thread_state();
if (state != nullptr && state->is_pending_interp_only_mode()) {
JvmtiEventController::enter_interp_only_mode();
}
}
- Add extra check of `JvmtiExport::can_support_virtual_threads()` when virtual
thread mount and unmount are posted.
- Minor: Added a `ThreadsListHandle` to the
`JvmtiEventControllerPrivate::enter_interp_only_mode`. It is needed because of
the dynamic creation of compensating carrier threads which is racy for JVMTI
`SetEventNotificationMode` implementation.
Performance mesurements:
- Without this fix the test provided by the bug submitter gives execution
numbers:
- no ClassLoad events enabled: 3251 ms
- ClassLoad events are enabled: 40534 ms
- With the fix:
- no ClassLoad events enabled: 3270 ms
- ClassLoad events are enabled: 3385 ms
Testing:
- Ran mach5 tiers 1-6, no regressions are noticed
-------------
Commit messages:
- 8308614: Enabling JVMTI ClassLoad event slows down vthread creation by
factor 10
Changes: https://git.openjdk.org/jdk/pull/16686/files
Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16686&range=00
Issue: https://bugs.openjdk.org/browse/JDK-8308614
Stats: 37 lines in 3 files changed: 24 ins; 4 del; 9 mod
Patch: https://git.openjdk.org/jdk/pull/16686.diff
Fetch: git fetch https://git.openjdk.org/jdk.git pull/16686/head:pull/16686
PR: https://git.openjdk.org/jdk/pull/16686
