On Mon, 8 May 2023 10:01:49 GMT, Viktor Klang <d...@openjdk.org> wrote:
>> Same as we saw with `isAlive` before: `LockSupport.park` implicitly provides >> a compiler barrier. This `done` should be at least "opaque" to carry the >> same effect. > > Yes, `park()` and `unpark()` having release and acquire semantics is not > documented > [here](https://docs.oracle.com/en/java/javase/20/docs/api/java.base/java/util/concurrent/locks/LockSupport.html#park()), > and the documentation for `LockSupport` explicitly says "Reliable usage > requires the use of volatile (or atomic) variables to control when to park or > unpark. Orderings of calls to these methods are maintained with respect to > volatile variable accesses, but not necessarily non-volatile variable > accesses." Irrespective of park/unpark barriers, the JIT should have hoisted `done` and rewritten as: if (!done) { while(true) { ... } } ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/13815#discussion_r1188051993
