On Thu, 31 Oct 2024 07:19:10 GMT, Alan Bateman <al...@openjdk.org> wrote:
>> This is an update to the Virtual thread implementation that we'd like to >> integrate in advance of JEP 491. >> >> The update removes the use of "temporary transitions", basically cases >> where the thread identity switches to the carrier thread to do something in >> the context of the carrier while a virtual thread is mounted. These cases >> create complexity for JVMTI and observability tools. It has also attracted >> attention in the review of the JEP 491 implementation as the object monitor >> changes have to deal with the possibility of entering monitors while in this >> state. There are 3 usages changes: >> >> 1. In submitRunContinuation the submit to the scheduler is changed so that >> it executes in the context of a virtual thread for cases where one virtual >> thread unparks another. This requires pinning to prevent preemption during >> this sensitive operation. ForkJoinPool.poolSubmit is changed so that it uses >> the identity of the carrier. This change has no impact on the uses of >> lazySubmit or externalSubmit. >> 2. Timed-park. The current implementation schedules/cancels the timer task >> with the virtual thread mounted. This runs in the context of the carrier as >> any contention would infer with thread state, park blocker and the parking >> permit. The implementation is changed to schedule the timeout after >> unmounting, and to cancel before re-mounting. The downside of this is that >> it will scheduled later (maybe 200us later than before). We could capture >> the time and adjust but it doesn't seem worth it. >> 3. jdk.tracePinnedThreads. This is a diagnostic option for finding usages of >> thread locals in code executed by virtual threads. This is changed so use a >> thread local to detect reentrancy. >> >> The changes means that notifyJvmtiHideFrames, its intrinsic, and the JVMTI >> "tmp VTMS_transition" bit go away. > > 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 four additional > commits since the last revision: > > - Fix typo in comment > - Merge branch 'master' into JDK-8343132 > - Merge branch 'master' into JDK-8343132 > - Initial commit Marked as reviewed by dholmes (Reviewer). ------------- PR Review: https://git.openjdk.org/jdk/pull/21735#pullrequestreview-2407378053
