224. Observing and monitoring virtual threads

Observing and monitoring virtual threads can be done in several ways. First, we can use Java Flight Recorder (JFR) – we introduced this tool in Chapter 6, Problem 143.

Using JFR

Among its reach list of events, JFR can monitor and record the following events related to virtual threads:

• jdk.VirtualThreadStart – this event is recorded when a virtual thread starts (by default, it is disabled)
• jdk.VirtualThreadEnd – this event is recorded when a virtual thread ends (by default, it is disabled)
• jdk.VirtualThreadPinned – this event is recorded when a virtual thread is parked while pinned (by default, it is enabled with a threshold of 20 ms)
• jdk.VirtualThreadSubmitFailed – this event is recorded if a virtual thread cannot be started or unparked (by default, it is enabled)

You can find all the JFR events at https://sap.github.io/SapMachine/jfrevents/.

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