On Fri, 8 Mar 2024 06:11:23 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 pull request now contains 26 commits:
>
> - Merge
> - review: minor tweak in test description of ObjectMonitorUsage.java
> - review: addressed more comments on the fix and new test
> - rename after merge: jvmti_common.h to jvmti_common.hpp
> - Merge
> - review: update comment in threads.hpp
> - fix deadlock with carrier threads starvation in ObjectMonitorUsage test
> - resolve merge conflict for deleted file objmonusage003.cpp
> - fix a typo in libObjectMonitorUsage.cpp
> - fix potential sync gap in the test ObjectMonitorUsage
> - ... and 16 more: https://git.openjdk.org/jdk/compare/de428daf...b97b8205
> Sorry I missed this response. I can't see a way to address spurious wakeups
> in this case as it needs to be a per-thread flag (so that each thread knows
> it was notified) but you don't know which thread will be notified in any
> given call to notify(). I also can't see how you can detect a spurious wakeup
> in this code. If they happen then a subtest may fail due to an unexpected
> number of re-entering threads. I think we will just have to see how stable
> the test is in practice.
Okay, thanks! Let's see if we ever encounter any spurious wakeup in this test.
Than you a lot for thorough review, David!
-------------
PR Comment: https://git.openjdk.org/jdk/pull/17680#issuecomment-1988074775
PR Comment: https://git.openjdk.org/jdk/pull/17680#issuecomment-1988076636
