> 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 ------------- Changes: - all: https://git.openjdk.org/jdk/pull/21735/files - new: https://git.openjdk.org/jdk/pull/21735/files/c88ce3dd..2d18c116 Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=21735&range=01 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21735&range=00-01 Stats: 54557 lines in 1036 files changed: 11998 ins; 40288 del; 2271 mod Patch: https://git.openjdk.org/jdk/pull/21735.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/21735/head:pull/21735 PR: https://git.openjdk.org/jdk/pull/21735
