On Mon, 17 Nov 2025 13:50:30 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: >> >> 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 two 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 >> >> 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 incrementally with one additional > commit since the last revision: > > 8366659: Addressed reviewer's comments. src/hotspot/share/runtime/objectMonitor.cpp line 1950: > 1948: // as having "-locked" the monitor, but the OS and > java.lang.Thread > 1949: // states will still report that the thread is blocked trying to > 1950: // acquire it. Q: I have a concern here. Did we have a similar inconsistency before? As I see, this can be observable not only by thread dumps but also by JVMTI in general (independently of the thread's suspend status). Dan, can you comment on this, please? test/hotspot/jtreg/serviceability/jvmti/SuspendWithObjectMonitorWait/SuspendWithObjectMonitorWait.java line 52: > 50: * @compile SuspendWithObjectMonitorWait.java > 51: * @run main/othervm/native -agentlib:SuspendWithObjectMonitorWait > SuspendWithObjectMonitorWait 3 > 52: */ Q: I'm not that happy with adding this complexity into one single test. Would it make sense to split `doWork1`, `doWork2` and `doWork3` tests into independent test sharing some parts, e.g. .cpp file, `SuspendWithObjectMonitorWaitWorker` class etc.? Then the only duplication will be the `main()` method. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/27040#discussion_r2535945583 PR Review Comment: https://git.openjdk.org/jdk/pull/27040#discussion_r2535957986
