On Tue, 2 Sep 2025 08:10:32 GMT, Anton Artemov <[email protected]> wrote:
> Hi, please consider the following changes: > > If suspension is allowed when a thread is re-entering an object monitor (OM), > then a following liveness issues can happen in the `ObjectMonitor::wait()` > method. > > The waiting thread is made to be a successor and is unparked. Upon a > suspension request, the thread will suspend itself whilst clearing the > successor. The OM will be left unlocked (not grabbed by any thread), while > the other threads are parked until a thread grabs the OM and the exits it. > The suspended thread is on the entry-list and can be selected as a successor > again. None of other threads can be woken up to grab the OM until the > suspended thread has been resumed and successfully releases the OM. > > This can happen in three places where the successor could be suspended: > > 1: > https://github.com/openjdk/jdk/blob/6322aaba63b235cb6c73d23a932210af318404ec/src/hotspot/share/runtime/objectMonitor.cpp#L1897 > > 2: > https://github.com/openjdk/jdk/blob/6322aaba63b235cb6c73d23a932210af318404ec/src/hotspot/share/runtime/objectMonitor.cpp#L1149 > > 3: > https://github.com/openjdk/jdk/blob/6322aaba63b235cb6c73d23a932210af318404ec/src/hotspot/share/runtime/objectMonitor.cpp#L1951 > > The issues are addressed by not allowing suspension in case 1, and by > handling the suspension request at a later stage, after the thread has > grabbed the OM in `reenter_internal()` in case 2. In case of a suspension > request, the thread exits the OM and enters it again once resumed. > > Case 3 is handled by not transferring a thread to the `entry_list` in > `notify_internal()` in case the corresponding JVMTI event is allowed. > Instead, a tread is unparked and let run. Since it is not on the > `entry_list`, it will not be chosen as a successor and it is no harm to > suspend it if needed when posting the event. > > Possible issue of posting a `waited` event while still be suspended is > addressed by adding a suspension check just before the posting of event. > > Tests are added. > > Tested in tiers 1 - 7. This pull request has now been integrated. Changeset: 1f3fd3da Author: Anton Artemov <[email protected]> URL: https://git.openjdk.org/jdk/commit/1f3fd3da1d24118a29d28f01d3fa59d7712607e5 Stats: 1390 lines in 9 files changed: 903 ins; 437 del; 50 mod 8366659: ObjectMonitor::wait() liveness problem with a suspension request Co-authored-by: Patricio Chilano Mateo <[email protected]> Co-authored-by: Daniel D. Daugherty <[email protected]> Reviewed-by: dcubed, sspitsyn, dholmes, pchilanomate ------------- PR: https://git.openjdk.org/jdk/pull/27040
