On Fri, 5 Nov 2021 20:46:21 GMT, Daniel D. Daugherty <dcu...@openjdk.org> wrote:
>> JvmtiThreadState objects point to JavaThread and vice versa, so I still >> don't see why you don't protect the first element. > > I've written up a rather long analysis about how the use of > `JvmtiThreadState_lock` > in `JvmtiEventControllerPrivate::recompute_enabled()` means that we can safely > traverse the JvmtiThreadState list returned by `JvmtiThreadState::first()` > without > racing with an exiting JavaThread. I've sent it to you via direct email. > > I could amend the comment above the ThreadsListHandle like this: > > // If we have a JvmtiThreadState, then we've reached the point where > // threads can exist so create a ThreadsListHandle to protect them. > // The held JvmtiThreadState_lock prevents exiting JavaThreads from > // being removed from the JvmtiThreadState list we're about to walk > // so this ThreadsListHandle exists just to satisfy the lower level sanity > // checks that the target JavaThreads are protected. > ThreadsListHandle tlh; Yes, this comment is good and it does explain why it's safe and why the TLH is there. Thanks for doing the deep dive and explanation. ------------- PR: https://git.openjdk.java.net/jdk/pull/4677
