RFR: 8331553: Windows JVM leaks Event and Thread handles when multiple threads are used

[Thomas Stuefe]

On Tue, 18 Jun 2024 21:01:15 GMT, Daniel Jeliński <djelinski at openjdk.org> wrote:

> 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?

Interesting, did not know that.

Apart from the unknown performance characteristics, what about backward compatibility? Do we care for Windows older than 8?

I share @dholmes-ora concern about scalibility. Your patch replaces the underlying mechanics for ObjectMonitor, right? We can have a lot of OMs, depending on how fast deflation is. Not many of them would be contended though.

IIRC The Renaissance philosophers benchmark is a good example of mass synchronisation. If you run this with UseHeavyMonitors, it would be a good test.

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PR Comment: https://git.openjdk.org/jdk/pull/19778#issuecomment-2178072230