On Thu, 22 Sep 2022 09:16:28 GMT, Serguei Spitsyn <sspit...@openjdk.org> wrote:
>> There are several places in VirtualThread class implementation where virtual >> threads are being mounted or unmounted, so there is a transition of the >> JavaThread identity from carrier thread to virtual thread and back. The >> execution state in such transitions is inconsistent, and so, has to be >> invisible to JVM TI agents. Such transitions are named as VTMS (virtual >> thread mount state) transitions, and there is a JVM TI mechanism which >> supports them. Besides normal VTMS transitions there are also a couple of >> performance-critical contexts (in `VirtualThread` methods: >> `scheduleUnpark()`, `cancel()` and `unpark()`) which can be named as >> temporary VTMS transitions. Execution state of such temporary VTMS >> transitions has to be also invisible to the JVM TI agent which is >> implemented in the current update. >> >> There are a couple of details of this fix to highlight: >> - A JavaThread which is in temporary VTMS transition is marked with a >> special bit `_is_in_tmp_VTMS_transition`. It is done with the native >> notification method `toggleJvmtiTmpVTMSTrans()`. >> - A couple of lambda form classes can be created in context of temporary >> VTMS transitions, so their `ClassLoad`, `ClassPrepare` and `CFLH` events are >> ignored. >> - Suspending threads in temporary transition is allowed. >> >> The fix was tested in Loom repository by using `JTREG_MAIN_WRAPPER=Virtual` >> mode of execution which forces all main threads to be run as virtual. All >> `JVM TI` and `JDI` tests were run on all platforms. It includes >> `Kitchensink` and `JCK` tests. Additionally, the fix was tested in the jdk >> 20 repository. It includes `JVM TI` and `JDI` tests and tiers 1-6. > > Serguei Spitsyn has updated the pull request incrementally with one > additional commit since the last revision: > > 1. addressed review comments from Chris; added VirtualThread.java update > from Alan Alan is currently investigating and testing his approach to get rid of temporary transitions. If it comes to be successful then I'll close this PR. Getting rid of temporary transitions is preferable as it will simplify the code a lot. However, I've pushed an update to complete my current chunk of work for safety. It includes two items: - an update from Alan, to get rid of some lambda form classes loading in context of temporary VTMS transition - update which address comments from Chris: - renaming of Thread class functions - changes in the function: `JvmtiEnvBase::get_cthread_last_java_vframe()` ------------- PR: https://git.openjdk.org/jdk/pull/10321
