On Wed, 29 Mar 2023 22:02:02 GMT, Daniel D. Daugherty <[email protected]>
wrote:
>> src/hotspot/share/runtime/threads.cpp line 1423:
>>
>>> 1421:
>>> 1422: JavaThread* Threads::owning_thread_from_object(ThreadsList * t_list,
>>> oop obj) {
>>> 1423: assert(SafepointSynchronize::is_at_safepoint(), "not safe outside
>>> of safepoint");
>>
>> `ObjectSynchronizer::get_lock_owner()` calls
>> `Threads::owning_thread_from_object()`
>> and I don't think you can assert that `ObjectSynchronizer::get_lock_owner()`
>> is only
>> called from a safepoint. In particular, `ThreadSnapshot::initialize()` calls
>> `ObjectSynchronizer::get_lock_owner()` and I believe that `initialize()`
>> function can
>> be called from non-safepoint places with M&M APIs...
>
> Update: In v35 you put back the `!UseFastLocking` check in
> `jmm_GetThreadInfo()`
> so now the `assert()` won't fire, but you've again changed the behavior of
> that API
> and now it will be able to observe fewer thread state changes than it did
> before.
Please explain why you think this is "not safe". Yes, you can observe state
that is in
the process of changing, but do you think that we'll see a crash with allowing
`Threads::owning_thread_from_object()` to be called from a non-safepoint place?
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PR Review Comment: https://git.openjdk.org/jdk/pull/10907#discussion_r1152536799
