> 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: fixed typo in VirtualThread.c ------------- Changes: - all: https://git.openjdk.org/jdk/pull/10321/files - new: https://git.openjdk.org/jdk/pull/10321/files/7ff72d7f..551d8d32 Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=10321&range=02 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10321&range=01-02 Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod Patch: https://git.openjdk.org/jdk/pull/10321.diff Fetch: git fetch https://git.openjdk.org/jdk pull/10321/head:pull/10321 PR: https://git.openjdk.org/jdk/pull/10321
