We use 2 ParkEvent instances per thread. The ParkEvent objects are never freed, but they are recycled when a thread dies, so the number of live ParkEvent instances is proportional to the maximum number of threads that were live at any time.
On Windows, the ParkEvent object wraps a kernel Event object. Kernel objects are a limited and costly resource. In this PR, I replace the use of kernel events with user-space synchronization. The new implementation uses WaitOnAddress and WakeByAddressSingle methods to implement synchronization. The methods are available since Windows 8. We only support Windows 10 and newer, so OS support should not be a problem. WaitOnAddress was observed to return spuriously, so I added the necessary code to recalculate the timeout and continue waiting. Tier1-5 tests passed. Performance tests were... inconclusive. For example, `ThreadOnSpinWaitProducerConsumer` reported 30% better results, while `LockUnlock.testContendedLock` results were 50% worse. Thoughts? ------------- Commit messages: - Implement PlatformEvent using WaitOnAddress Changes: https://git.openjdk.org/jdk/pull/19778/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19778&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8331553 Stats: 75 lines in 3 files changed: 9 ins; 54 del; 12 mod Patch: https://git.openjdk.org/jdk/pull/19778.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/19778/head:pull/19778 PR: https://git.openjdk.org/jdk/pull/19778
