Fantastic Virtual Threads and How to Monitor Them

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06 Dec 2023 Balkrishna Rawool Fantastic Virtual Threads and How to Monitor Them

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2 Balkrishna Rawool IT Chapter Lead, ING Bank @BalaRawool

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Fantastic virtual threads

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4 Virtual Threads JVM OS Platform Threads Platform Threads: Ø Thin wrapper over OS threads Ø One-to-one mapping with OS threads Ø Thread pools Virtual Threads Virtual Threads: Ø Lightweight user threads Ø Highly scalable Ø No need for pooling

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8 Virtual Thread Scheduler Platform/ Carrier Thread Virtual Threads

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How to create virtual threads?

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Be aware of pinning! 10 Ø Pinning is when virtual thread cannot be unmounted from the carrier thread. Ø It happens when: Ø Virtual thread is executing a synchronized code-block/ method or Ø Virtual thread is executing a native call Ø In case of ‘synchronized’ Ø Problem if you’re doing long-running/ blocking operations inside synchronized Ø Use ReentrantLock Ø In future, this may not pin the virtual thread

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How to monitor them (virtual threads)?

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Monitoring toolset 12 Ø JFR (JDK Flight Recorder) Ø JMC (JDK Mission Control) Ø VisualVM Ø jcmd

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jcmd 13 Ø Helps us to send diagnostic command requests to the JVM Ø Many commands are available Ø JFR Ø Garbage collection Ø JVM Ø Must be used on the same machine where the JVM is running Ø Usage: Ø New: Thread dump in JSON format jcmd [options] jcmd Thread.dump_to_file –format=json

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JFR (JDK Flight Recorder) 14 Ø An event-based tracing framework, built into the Java Runtime. Ø It gathers detailed low-level information about how a JVM or a Java application is behaving. Ø It maintains low overhead (< 1%). Ø Data is continuously recorded, optionally written to disk. Ø It records data about JVM events. Ø Types of events: Ø Duration events Ø Instant events Ø Sample events Ø Custom events

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JFR (JDK Flight Recorder) 15 Ø New events added for supporting virtual threads: Ø jdk.VirtualThreadStart Ø jdk.VirtualThreadEnd Ø jdk.VirtualThreadPinned Ø jdk.VirtualThreadSubmitFailed Ø Starting JFR Ø During starting the application Ø Using jcmd Ø From JMC Ø JEP-349 Enables JFR Event Streaming java –XX:StartFlightRecording:filename=./recordings/myapp.jfr,dumponexit=true … jcmd 1234 JFR.start jcmd 1234 JFR.dmp filename=./recordings/myapp.jfr

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JMC 16 Ø Control panel for managing, monitoring and troubleshooting JVM applications Ø Gives a lot of info including CPU usage, Memory usage, Threads and MBeans Ø You can also run jcmd commands from JMC Ø Views: Ø MBean Server: Info from JMX (Java Management Extension) Ø JDK Flight Recorder Ø Plug-ins

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Visual VM 17 Ø Visual interface for viewing detailed information about Java applications Ø Connects with local and remote applications. Ø Provides info about CPU usage, Memory usage, Threads, Classes etc. Ø In terms of features quite similar to JMC

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Monitoring toolset - summary 18 Ø JFR is quite powerful and provide lots of info with low overhead Ø jcmd is quite useful for creating/managing recordings and for other diagnostics Ø JMC and VisualVM are feature rich and provide visual interface Ø Virtual thread support Ø 4 new events in JFR Ø Thread dump in JSON format via jcmd Ø JFR and jcmd are available as part of JDK. JMC and VisualVM are available externally.