The cur_stack_depth is the cache that is maintained in interponly mode to optimize getting number of thread in the debugger operations.
Historically, it cause a lot of issues. Most oftenly, related with wrong calculation in the case if stack depth changed during yield or stack debugger operations. Also, there is a gep between decrement of cur_stack_depth and actual stack change where cur_stack_depth is invalid. The current problem happens when operations like PopFrame or ForceEarlyReturn happen when MethodExit is completed and cur_stack_depth is decremented while physical stack is not removed yet. It is reproduced by internal stress test. We discussed privately with @sspitsyn and there is an idea that this cache is not worth to maintain. It is used in interp-only mode which is slow already. Really this cur_stack_depth() is not so often used and quite often invalidated. Currently, the function is uses in 3 places: 1. JvmtiExport::continuation_yield_cleanup, where invalidate_cur_stack_depth() is called right before cur_stack_depth(), making the caching useless. So no performance degradation here is expected. 2. In the post_method_exit_inner when 'ets->has_frame_pops()' is true. And actually it might crash in this place. This happens when NotifyFramePop event is requested. It doesn't require the interponly mode after fix of [JDK-6960970](https://bugs.openjdk.org/browse/JDK-6960970) Debugger very slow during stepping 3. JvmtiThreadState::process_pending_step_for_popframe which is called in UpdateForPopTopFrameClosure during PopFrame when performance is not important. Also, the crash happens when 'process_pending_step_for_popframe' is executed while cache doesn't correspond the actual state. So I wonder if there are any scenario when the impact of the removal of cur_stack_depth is so significant that it makes sense to still maintain it? i am running tier1-8 and some internal stress testing to verify this fix. --------- - [x] I confirm that I make this contribution in accordance with the [OpenJDK Interim AI Policy](https://openjdk.org/legal/ai). ------------- Commit messages: - removed unused constant - 8383879 Changes: https://git.openjdk.org/jdk/pull/31389/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=31389&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8383879 Stats: 103 lines in 8 files changed: 0 ins; 97 del; 6 mod Patch: https://git.openjdk.org/jdk/pull/31389.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/31389/head:pull/31389 PR: https://git.openjdk.org/jdk/pull/31389
