> 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 incrementally with one additional commit since the last revision: 8366659: Modified the comment. ------------- Changes: - all: https://git.openjdk.org/jdk/pull/27040/files - new: https://git.openjdk.org/jdk/pull/27040/files/95cf01f6..949db95e Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=27040&range=22 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27040&range=21-22 Stats: 16 lines in 1 file changed: 10 ins; 0 del; 6 mod Patch: https://git.openjdk.org/jdk/pull/27040.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/27040/head:pull/27040 PR: https://git.openjdk.org/jdk/pull/27040
