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eclipse-openj9 / openj9

Eclipse OpenJ9: A Java Virtual Machine for OpenJDK that's optimized for small footprint, fast start-up, and high throughput. Builds on Eclipse OMR (https://github.com/eclipse/omr) and combines with the Extensions for OpenJDK for OpenJ9 repo.
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Thread::getState is a scalability issue #17251

Open DanHeidinga opened 1 year ago

DanHeidinga commented 1 year ago

Java -version output

All versions

Summary of problem

The Netty project was using Thread::getState on a non-current thread. Due to needing to halt the thread for inspection, there was a scalability issue when using Netty on OpenJ9.

They've worked around it by calling Thread::isAlive instead for OpenJ9, but this kind of lingering scalability issue may affect others as well.

Original issue: https://github.com/netty/netty/issues/13347#issuecomment-1518537895 Workaround: https://github.com/netty/netty/pull/13357

DanHeidinga commented 1 year ago

fyi @babsingh @gacholio

babsingh commented 1 year ago

Potential solution: Add a field in j.l.Thread which will store the current state of the Java thread. It will be atomically updated as the Java thread goes through the various state transitions in native and Java code. With this approach, Thread::getState will require to atomically read the new field without the need to halt the thread for inspection.

gacholio commented 1 year ago

We've talked about this for years - there's no need for an atomic update. Like so many APIs, the return value is momentary, likely to be different a few instructions later.