On Wed, 7 Feb 2024 07:02:11 GMT, Serguei Spitsyn <sspit...@openjdk.org> wrote:
>> The implementation of the JVM TI `GetObjectMonitorUsage` does not match the
>> spec.
>> The function returns the following structure:
>>
>>
>> typedef struct {
>> jthread owner;
>> jint entry_count;
>> jint waiter_count;
>> jthread* waiters;
>> jint notify_waiter_count;
>> jthread* notify_waiters;
>> } jvmtiMonitorUsage;
>>
>>
>> The following four fields are defined this way:
>>
>> waiter_count [jint] The number of threads waiting to own this monitor
>> waiters [jthread*] The waiter_count waiting threads
>> notify_waiter_count [jint] The number of threads waiting to be notified by
>> this monitor
>> notify_waiters [jthread*] The notify_waiter_count threads waiting to be
>> notified
>>
>> The `waiters` has to include all threads waiting to enter the monitor or to
>> re-enter it in `Object.wait()`.
>> The implementation also includes the threads waiting to be notified in
>> `Object.wait()` which is wrong.
>> The `notify_waiters` has to include all threads waiting to be notified in
>> `Object.wait()`.
>> The implementation also includes the threads waiting to re-enter the monitor
>> in `Object.wait()` which is wrong.
>> This update makes it right.
>>
>> The implementation of the JDWP command `ObjectReference.MonitorInfo (5)` is
>> based on the JVM TI `GetObjectMonitorInfo()`. This update has a tweak to
>> keep the existing behavior of this command.
>>
>> The follwoing JVMTI vmTestbase tests are fixed to adopt to the
>> `GetObjectMonitorUsage()` correct behavior:
>>
>> jvmti/GetObjectMonitorUsage/objmonusage001
>> jvmti/GetObjectMonitorUsage/objmonusage003
>>
>>
>> The following JVMTI JCK tests have to be fixed to adopt to correct behavior:
>>
>> vm/jvmti/GetObjectMonitorUsage/gomu001/gomu00101/gomu00101.html
>> vm/jvmti/GetObjectMonitorUsage/gomu001/gomu00101/gomu00101a.html
>> vm/jvmti/GetObjectMonitorUsage/gomu001/gomu00102/gomu00102.html
>> vm/jvmti/GetObjectMonitorUsage/gomu001/gomu00102/gomu00102a.html
>>
>>
>>
>> A JCK bug will be filed and the tests have to be added into the JCK problem
>> list located in the closed repository.
>>
>> Also, please see and review the related CSR:
>> [8324677](https://bugs.openjdk.org/browse/JDK-8324677): incorrect
>> implementation of JVM TI GetObjectMonitorUsage
>>
>> The Release-Note is:
>> [8325314](https://bugs.openjdk.org/browse/JDK-8325314): Release Note:
>> incorrect implementation of JVM TI GetObjectMonitorUsage
>>
>> Testing:
>> - tested with mach5 tiers 1-6
>
> Serguei Spitsyn has updated the pull request with a new target base due to a
> merge or a rebase. The incremental webrev excludes the unrelated changes
> brought in by the merge/rebase. The pull request contains three additional
> commits since the last revision:
>
> - Merge
> - review: thread in notify waiter list can't be BLOCKED
> - 8324677: Specification clarification needed for JVM TI
> GetObjectMonitorUsage
Based on Dan's analysis I would have to go back and redo the complete analysis
for myself. :( I think the only way to make sense of this is to actually set up
scenarios where we have different threads contending on entry, different
threads waiting and different threads re-entering after being notified, and see
what values actually get returned in each case.
I think the `pending_current_monitor` issue may be a distinct/different issue.
I can easily imagine that this was overlooked when we introduced the "wait
morphing" rather than have the notified/timed-out/interrupted waiters actually
place themselves on the entry queue.
-------------
PR Comment: https://git.openjdk.org/jdk/pull/17680#issuecomment-1933469232
