RFR: 8364819: Post-integration cleanups for JDK-8359820 [v2]

[Aleksey Shipilev]

On Wed, 6 Aug 2025 12:15:57 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Anton Artemov has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8364819: Fixed brace in the test
>
> src/hotspot/share/utilities/vmError.cpp line 108:
> 
>> 106: const intptr_t    VMError::segfault_address = pd_segfault_address;
>> 107: volatile Thread* VMError::_handshake_timed_out_thread = nullptr;
>> 108: volatile Thread* VMError::_safepoint_timed_out_thread = nullptr;
> 
> I should have picked this up previously but `volatile` generally serves no purpose for inter-thread consistency. If we need to guarantee visibility between the signaller and signalee, then we need a fence to ensure that. Or we can skip the fence (and volatile) and note that this will usually, but perhaps not always, work fine. (I note that `pthread_kill` is not specified as a memory synchronizing operation, but I strongly suspect it has to have its own internal memory barriers that we would be piggy-backing on.)

I am pretty sure the memory consistency here is irrelevant, given that: a) the `Thread` in question is likely already initialized for a long time, so it is unlikely we will lose anything release-acquire-wise; b) we only use these for pointer comparisons.

But since we are here, and in the interest of clarity and avoiding future surprises, we can just summarily wrap these with `Atomic::release_store` and `Atomic::load_acquire` to be extra paranoidly safe. This is a failing path, so we don't care about performance, and would like to avoid a secondary crash in error handler some time in the future, if anyone reads anything from these threads.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/26656#discussion_r2257071709