On Wed, 25 Aug 2021 22:05:24 GMT, Vladimir Ivanov <vliva...@openjdk.org> wrote:
> Get rid of WeakReference-based logic in > DirectMethodHandle::checkInitialized() and reimplement it with > `Unsafe::ensureClassInitialized()`/`shouldBeInitialized()`. > > The key observation is that `Unsafe::ensureClassInitialized()` does not block > the initializing thread. > > Also, removed `Unsafe::shouldBeInitialized()` in > `DMH::shouldBeInitialized(MemberName)` to save on calling into the VM. > `Unsafe::ensureClassInitialized()` already has a fast-path check which checks > whether the class is fully initialized or not. > > Testing: tier1 - tier6 src/java.base/share/classes/java/lang/invoke/DirectMethodHandle.java line 385: > 383: Class<?> defc = member.getDeclaringClass(); > 384: UNSAFE.ensureClassInitialized(defc); // initialization barrier; > blocks unless called by the initializing thread > 385: return !UNSAFE.shouldBeInitialized(defc); // keep the barrier if > the initialization is still in progress I think some more elaborate commentary about the possibility of this being called while <clinit> of defc is already on the call stack, would be worthwhile - the existing comments are a little too subtle IMO. UNSAFE.ensureClassInitialized(defc); // Once we get here either defc was fully initialized by another thread, or // defc was already being initialized by the current thread. In the latter case // the barrier must remain. We can detect this simply by checking if initialization // is still needed. return !UNSAFE.shouldBeInitialized(defc); ------------- PR: https://git.openjdk.java.net/jdk/pull/5258
