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Enhancement
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Resolution: Done
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Major
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None
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None
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False
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False
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[PR opened by pruivo]
Looking at stack traces, it seems EPollSelectorImpl.doSelect never blocks
and keeps the virtual thread "pinned" to the carrier thread
It can be observed with the Draw demo. Setting the JVM options -Djdk.virtualThreadScheduler.parallelism=1 -Djdk.virtualThreadScheduler.maxPoolSize=1, which forces the JVM to use a single carrier thread, the demo does not work, and no other node can join. Note, this affects applications running with JDK < 24
With OpenJDK Runtime Environment Temurin-21.0.8+9 (build 21.0.8+9-LTS), the stack trace shows:
#42 "NioServer.Selector [/127.0.0.1:7900]-6,draw,pedro-desktop-6500" virtual
java.base/sun.nio.ch.EPoll.wait(Native Method)
java.base/sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:121)
java.base/sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:130)
java.base/sun.nio.ch.SelectorImpl.select(SelectorImpl.java:147)
org.jgroups.blocks.cs.NioBaseServer$Acceptor.doSelect(NioBaseServer.java:169)
org.jgroups.blocks.cs.NioBaseServer$Acceptor.run(NioBaseServer.java:123)
java.base/java.lang.VirtualThread.run(VirtualThread.java:329)
With OpenJDK Runtime Environment Temurin-25+36 (build 25+36-LTS), the EPollSelectorImpl.doSelect has been patched and parks the virtual thread.
#36 "NioServer.Selector [/127.0.0.1:7901]-6,draw,pedro-desktop-37567" virtual WAITING 2026-01-15T18:19:04.378511174Z
at java.base/java.lang.VirtualThread.park(VirtualThread.java:738)
at java.base/java.lang.System$1.parkVirtualThread(System.java:2284)
at java.base/java.util.concurrent.locks.LockSupport.park(LockSupport.java:367)
at java.base/sun.nio.ch.Poller.poll(Poller.java:197)
at java.base/sun.nio.ch.Poller.pollSelector(Poller.java:161)
at java.base/sun.nio.ch.EPollSelectorImpl.untimedPoll(EPollSelectorImpl.java:146)
at java.base/sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:111)
at java.base/sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:130)
- locked <sun.nio.ch.Util$2@5069e038>
- locked <sun.nio.ch.EPollSelectorImpl@a310d5b>
at java.base/sun.nio.ch.SelectorImpl.select(SelectorImpl.java:147)
at org.jgroups.blocks.cs.NioBaseServer$Acceptor.doSelect(NioBaseServer.java:169)
at org.jgroups.blocks.cs.NioBaseServer$Acceptor.run(NioBaseServer.java:123)
at java.base/java.lang.VirtualThread.run(VirtualThread.java:456)
