On Wed, 12 Nov 2025 13:29:07 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 deadlock is possible. There are two places where it can happen: >> >> 1) 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. >> >> 2) The race between suspension and retry: the thread could reacquire the OM >> and complete the wait() code in full, but then on return to Java it will be >> suspended while holding the OM. >> >> 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. >> >> The JVMTI `waited` event posting (2nd one) is postponed until the suspended >> thread is resumed and has entered the OM again. The `enter` to the OM (in >> case `ExitOnSuspend` did exit) is done without posting any events. >> >> Tests are added for both scenarios. >> >> 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 20 commits: > > - Merge remote-tracking branch 'origin/master' into > JDK-8366659-OM-wait-suspend-deadlock > - 8366659: Fixed lines in tests. > - Merge remote-tracking branch 'origin/master' into > JDK-8366659-OM-wait-suspend-deadlock > - 8366659: Added a comment to a boolean arg for enter() > - Merge remote-tracking branch 'origin/master' into > JDK-8366659-OM-wait-suspend-deadlock > - Merge remote-tracking branch 'origin/master' into > JDK-8366659-OM-wait-suspend-deadlock > - 8366659: Fixed new lines. > - Merge remote-tracking branch 'origin/master' into > JDK-8366659-OM-wait-suspend-deadlock > - 8366659: Removed incorrect assert, > - 8366659: Fixed merge conflict > - ... and 10 more: https://git.openjdk.org/jdk/compare/400a83da...702880c6 So the bug report talks about two different deadlocks and we have added two new test cases to SuspendWithObjectMonitorWait.java. I think the new `doWork2` test case is added to catch deadlock-1 when we have a suspended thread made the successor over and over again so that none of the other contending threads ever get the monitor even though it is unlocked. I think the new `doWork3` test case is added to catch deadlock-2 where the waiting thread manages to re-enter the monitor and then gets suspended while on its way back to Java. @toxaart and/or @pchilano - Please verify my understanding of this mapping from the two new test cases to the two deadlocks. Thanks! ------------- PR Comment: https://git.openjdk.org/jdk/pull/27040#issuecomment-3529662045
