On Wed, 14 Feb 2024 02:18:58 GMT, David Holmes <dhol...@openjdk.org> wrote:
>> 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 five additional
>> commits since the last revision:
>>
>> - Merge
>> - review: fixed issues in get_object_monitor_usage; extended test coverage
>> in objmonusage003
>> - Merge
>> - review: thread in notify waiter list can't be BLOCKED
>> - 8324677: Specification clarification needed for JVM TI
>> GetObjectMonitorUsage
>
> src/hotspot/share/runtime/threads.cpp line 1200:
>
>> 1198: if (pending == monitor ||
>> 1199: (waiting == monitor &&
>> JavaThreadStatus::BLOCKED_ON_MONITOR_ENTER ==
>> 1200: java_lang_Thread::get_thread_status(p->vthread_or_thread()))
>
> This code seems extremely racy. Is there anything that is stopping the target
> thread from running while we attempt this inspection of the oop state? If it
> was waiting and was interrupted or timed-out then we could mistakenly think
> it was still pending entry to this monitor when in fact it is not.
> It is also a shame that we have to reach up into the oop thread state to
> figure out if if it is blocked on re-entry ...
The function `get_pending_threads()` is executed only by the
VM_GetObjectMonitorUsage operation.
I've added this assert there:
`assert(Thread::current()->is_VM_thread(), "Must be the VM thread");`
Does it address your concern?
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/17680#discussion_r1489379382
