On Fri, 9 Jan 2026 12:05:37 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. > > Anton Artemov has updated the pull request with a new target base due to a > merge or a rebase. The pull request now contains 44 commits: > > - 8366659: Fixed year in the copyright. > - Merge remote-tracking branch 'origin/master' into > JDK-8366659-OM-wait-suspend-deadlock > - 8366659: Removed ClearSuccOnSuspend > - 8366659: Fixed liveness problem. > - Merge remote-tracking branch 'origin/master' into > JDK-8366659-OM-wait-suspend-deadlock > - 8366659: Fixed build problem. > - 8366659: Fixed build issue. > - 8366659: Changed the way how notify_internal works if JVMTI monitor waited > event allowed. > - Merge remote-tracking branch 'origin/master' into > JDK-8366659-OM-wait-suspend-deadlock > - 8366659: Fixed semi-broken tests > - ... and 34 more: https://git.openjdk.org/jdk/compare/a01283a5...21b83214 See the original issue from JDK1.3.1 here: [JDK-4413752](https://bugs.openjdk.org/browse/JDK-4413752) Linux: suspended thread blocks raw ObjectMonitor entry ------------- PR Comment: https://git.openjdk.org/jdk/pull/27040#issuecomment-3762029149
