RFR: 8338379: Accesses to class init state should be properly synchronized [v2]

[Aleksey Shipilev]

On Fri, 27 Sep 2024 18:59:36 GMT, Martin Doerr <mdoerr at openjdk.org> wrote:

> Nevertheless, the aforementioned `membar_storestore()` follows the allocation immediately and it includes an acquire barrier for the current thread, too.

OK, I see what you are getting at. But isn't that barrier still too late? See:


Thread 1 (in "new A()"):
  <runtime check fires> 
  <clinit runs>
  IK::init_state = fully_initialized
  [stalls]

Thread 2: (also in "new A()"):
  <runtime check passes: IK::init_state == fully_initialized>
  <allocates>
  membar_storestore(); // <---- nothing to cumulate with yet
  <constructor runs>  // not seeing <clinit> result fully, no barriers!

Thread 1:
  [resumes]
  <allocates>
  membar_storestore(); // <---- too late!

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PR Comment: https://git.openjdk.org/jdk/pull/21110#issuecomment-2379895063