> This is the implementation of JEP 491: Synchronize Virtual Threads without > Pinning. See [JEP 491](https://bugs.openjdk.org/browse/JDK-8337395) for > further details. > > In order to make the code review easier the changes have been split into the > following initial 4 commits: > > - Changes to allow unmounting a virtual thread that is currently holding > monitors. > - Changes to allow unmounting a virtual thread blocked on synchronized trying > to acquire the monitor. > - Changes to allow unmounting a virtual thread blocked in `Object.wait()` and > its timed-wait variants. > - Changes to tests, JFR pinned event, and other changes in the JDK libraries. > > The changes fix pinning issues for all 4 ports that currently implement > continuations: x64, aarch64, riscv and ppc. Note: ppc changes were added > recently and stand in its own commit after the initial ones. > > The changes fix pinning issues when using `LM_LIGHTWEIGHT`, i.e. the default > locking mode, (and `LM_MONITOR` which comes for free), but not when using > `LM_LEGACY` mode. Note that the `LockingMode` flag has already been > deprecated ([JDK-8334299](https://bugs.openjdk.org/browse/JDK-8334299)), with > the intention to remove `LM_LEGACY` code in future releases. > > > ## Summary of changes > > ### Unmount virtual thread while holding monitors > > As stated in the JEP, currently when a virtual thread enters a synchronized > method or block, the JVM records the virtual thread's carrier platform thread > as holding the monitor, not the virtual thread itself. This prevents the > virtual thread from being unmounted from its carrier, as ownership > information would otherwise go wrong. In order to fix this limitation we will > do two things: > > - We copy the oops stored in the LockStack of the carrier to the stackChunk > when freezing (and clear the LockStack). We copy the oops back to the > LockStack of the next carrier when thawing for the first time (and clear them > from the stackChunk). Note that we currently assume carriers don't hold > monitors while mounting virtual threads. > > - For inflated monitors we now record the `java.lang.Thread.tid` of the owner > in the ObjectMonitor's `_owner` field instead of a JavaThread*. This allows > us to tie the owner of the monitor to a `java.lang.Thread` instance, rather > than to a JavaThread which is only created per platform thread. The tid is > already a 64 bit field so we can ignore issues of the counter wrapping around. > > #### General notes about this part: > > - Since virtual threads don't need to worry about holding monitors anymo...
Patricio Chilano Mateo has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 84 commits: - Use get_method_name + copyright revert in jvmtiThreadState.cpp - Merge branch 'master' into JDK-8338383 - Add @requires vm.continuations to CancelTimerWithContention.java - Use JvmtiVTMSTransitionDisabler::VTMS_vthread_mount/unmount - Use is_top_frame boolean in FreezeBase::check_valid_fast_path() - Move load of _lock_id in C2_MacroAssembler::fast_lock - Add --enable-native-access=ALL-UNNAMED to SynchronizedNative.java - Update comment for _cont_fastpath - Add ReflectionCallerCacheTest.java to test/jdk/ProblemList-Xcomp.txt - Use ThreadIdentifier::initial() in ObjectMonitor::owner_from() - ... and 74 more: https://git.openjdk.org/jdk/compare/d3c042f9...62b16c6a ------------- Changes: https://git.openjdk.org/jdk/pull/21565/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21565&range=02 Stats: 9939 lines in 247 files changed: 7131 ins; 1629 del; 1179 mod Patch: https://git.openjdk.org/jdk/pull/21565.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/21565/head:pull/21565 PR: https://git.openjdk.org/jdk/pull/21565
