This is a regression from [JDK-8315884](https://bugs.openjdk.org/browse/JDK-8315884).
When using `+UseObjectMonitorTable` monitors are inflated in a locked state effectively blocking out deflation. `LightweightSynchronizer::enter_for` assumed this to be true. But when the `-UseObjectMonitorTable` path was added `// Do the old inflate and enter.` this is no longer true as it first inflates a monitor in an unlocked state and then tries to lock. We need to introduce a retry loop similar to what was used before [JDK-8315884](https://bugs.openjdk.org/browse/JDK-8315884). I propose we add this retry loop for both cases, to decouple the `LightweightSynchronizer::enter_for` from how lock elimination is done. With a retry loop, the only requirements for using `LightweightSynchronizer::enter_for` is that the Object locked on cannot have been locked on by another thread, i.e. there is no contention, but makes no assumptions on the interaction with the deflation thread. For `-UseObjectMonitorTable` 7bdbe114eb57fe7310f9664a434c4d9203e656fc should be enough, as it will assist the deflating thread with deflation, so the second call must succeed. However `+UseObjectMonitorTable` cannot do this so it must wait for the deflating thread to make progress. But as mentioned above, this would only happen if partial lock elimination is performed. E.g. Object o = new Object(); synchronized(o) { o.wait(1); } synchronized(o) { deoptimize(); } got transformed to Object o = new Object(); synchronized(o) { o.wait(1); } // synchronized(o) { Eliminated lock deoptimize(); // } As far as I can tell, this does not happen. But I do not want to couple lock elimination decision with `LightweightSynchronizer::enter_for`. So I propose a retry loop instead of just the two calls. After this change the only prerequisite for using `LightweightSynchronizer::enter_for` is that the object being synchronized can not have been reached by another JavaThread (except the deflating thread). So there may never be contention, but there may be deflation. ------------- Commit messages: - Decouple from EA and potential partial lock elimination - 8341819: LightweightSynchronizer::enter_for races with deflation Changes: https://git.openjdk.org/jdk/pull/21420/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21420&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8341819 Stats: 19 lines in 2 files changed: 17 ins; 0 del; 2 mod Patch: https://git.openjdk.org/jdk/pull/21420.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/21420/head:pull/21420 PR: https://git.openjdk.org/jdk/pull/21420
