On Thu, 15 Feb 2024 19:55:08 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: JDWP monitor_info spec clarification; removed debugging code from
> objmonusage001
Thanks for the test updates.
A couple of other queries.
src/hotspot/share/prims/jvmtiEnvBase.cpp line 1496:
> 1494: nWant = wantList->length();
> 1495:
> 1496: if (mon != nullptr) {
Shouldn't the call to `get_pending_threads` only happen if `mon != nullptr`?
Otherwise the `wantList` has to be empty.
src/hotspot/share/prims/jvmtiEnvBase.cpp line 1500:
> 1498: for (int i = 0; i < nWait; i++) {
> 1499: if (waiter == nullptr || (i != 0 && waiter ==
> mon->first_waiter())) {
> 1500: // robustness: the waiting list has gotten smaller
We are at a safepoint so I don't see how the wait list can shrink. I initially
thought perhaps a waiter could timeout, but the code that does the timed park
is wrapped in ` ThreadBlockInVMPreprocess` which will block at a safepoint if
one is active.
-------------
PR Review: https://git.openjdk.org/jdk/pull/17680#pullrequestreview-1884365884
PR Review Comment: https://git.openjdk.org/jdk/pull/17680#discussion_r1491992136
PR Review Comment: https://git.openjdk.org/jdk/pull/17680#discussion_r1491997307
