On Tue, 5 Mar 2024 03:40:04 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 incrementally with one
> additional commit since the last revision:
>
> review: addressed more comments on the fix and new test
Updates look good. A couple of minor commenst.
src/hotspot/share/prims/jvmtiEnvBase.cpp line 1507:
> 1505: nWait = 0;
> 1506: for (ObjectWaiter* waiter = mon->first_waiter();
> 1507: waiter != nullptr && (nWait == 0 || waiter !=
> mon->first_waiter());
Sorry I do not understand the logic of this line. `waiters` is just a
linked-list of `ObjectWaiter`s so all we need to do is traverse it and count
the number of elements.
test/hotspot/jtreg/serviceability/jvmti/ObjectMonitorUsage/ObjectMonitorUsage.java
line 36:
> 34: * - unowned object without any waiting threads
> 35: * - unowned object with threads waiting to be notified
> 36: * - owned object without any waiting threads
You could say "threads waiting" in all cases - it looks odd to reverse it for
two cases.
-------------
PR Review: https://git.openjdk.org/jdk/pull/17680#pullrequestreview-1915963487
PR Review Comment: https://git.openjdk.org/jdk/pull/17680#discussion_r1512195706
PR Review Comment: https://git.openjdk.org/jdk/pull/17680#discussion_r1512197846
