On Tue, 26 Sep 2023 02:30:25 GMT, David Holmes <dhol...@openjdk.org> wrote:
>>> Ah! I guess we get used to talking about "at a safepoint" when we really
>>> mean "at a fixed point in time". So the VM is not necessarily at a
>>> safepoint, but everything is fixed. So invariants may not hold, but the
>>> state cannot change.
>>
>> Correct!
>>
>>> So in the current context the anonymous owner should be found ...
>>
>> That's what I concluded based on Roman's description of how things work.
>>
>>> I guess the question to be answered is how the code tries to find an
>>> anonymous owner? I'm not sure how you can find it.
>>
>> I'm not sure yet. I'll need to have a look.
>
> AFAICS we update the owner to the real thread before we remove the object
> from the lock stack. So if we see the object monitor is anonymously owned
> then we should find the monitor object in a thread's lockstack.
Correction, there is one code path where we pop the lockstack first and then
update the owner:
ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
if (LockingMode == LM_LIGHTWEIGHT && monitor->is_owner_anonymous()) {
// It must be owned by us. Pop lock object from lock stack.
LockStack& lock_stack = current->lock_stack();
oop popped = lock_stack.pop();
assert(popped == object, "must be owned by this thread");
monitor->set_owner_from_anonymous(current);
}
monitor->exit(current);
we should probably do this the other way around.
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PR Review Comment: https://git.openjdk.org/jdk/pull/15907#discussion_r1336558790
