On Wed, 4 Feb 2026 08:40:12 GMT, Alan Bateman <[email protected]> wrote:
>> JDK-8364343 upgraded the virtual thread transition management to be >> independent of JVMTI. We can update java_lang_Thread::async_get_stack_trace >> to use it and remove the suspend + retry code from Thread.getStackTrace. >> >> A summary of the changes: >> >> - java_lang_Thread::async_get_stack_trace is changed to use the new >> handshake op so it can be called to get the stack trace of a started thread >> in any state >> - Thread::getStackTrace is changed to use async_get_stack_trace for all cases >> - The SUSPENDED substate in VirtualThread is removed >> - JVM_CreateThreadSnapshot is changed to be usable when JVMTI is not >> compiled in >> - ThreadSnapshotFactory::get_thread_snapshot is changed to not upcall to >> StackTraceElement to complete the init of the stack trace >> >> The changes mean that Thread::getStackTrace may be slower when sampling a >> virtual thread in transition. This case should be rare, and it isn't really >> a performance critical op anyway. I prototyped use a spin loop and an >> increasing wait time in MountUnmountDisabler::disable_transition_for_one to >> avoid the wait(10) but decided to leave it out for now. Future work may >> examine this issue as there may be other cases (with JVMTI) that would >> benefit from avoiding the wait. >> >> A future PR might propose to change Thread.getStackTrace to use >> ThreadSnapshot and allow java_lang_Thread::async_get_stack_trace be removed. >> This requires more extensive changes to ThreadSnapshotFactory to reduce >> overhead when only the stack trace is required. >> >> Testing: tier1-5. The changes has been already been tested in the loom repo >> for a few months. > > Alan Bateman has updated the pull request with a new target base due to a > merge or a rebase. The incremental webrev excludes the unrelated changes > brought in by the merge/rebase. The pull request contains seven additional > commits since the last revision: > > - Merge branch 'master' into JDK-8376568 > - Merge branch 'master' into JDK-8376568 > - Review feedback > - Improve asserts > - Cleanup > - Merge branch 'master' into Thread.getStackTrace > - Initial commit Thanks for the reviews and comments. ------------- PR Comment: https://git.openjdk.org/jdk/pull/29461#issuecomment-3853761047
