Thread pinning detection with JFR and Spring Boot

This application illustrates how to integrate JFR (Java Flight Recorder) Event Streaming with Spring Boot for monitoring of pinned threads.

The approach implemented here has been described in details in the dedicated blog post.

High-level overview

• JFR event streaming session running in background (JfrEventLifecycle.java)
• Custom jdk.VirtualThreadPinned JFR event handler, logging event details and reporting its duration as a Micrometer Timer (JfrVirtualThreadPinnedEventHandler.java)
• HTTP endpoint for causing thread pinning on demand (ThreadPinningController.java)

Requirements

• Java 21+
• Maven 3.9+ (compatible wrapper provided)

Running the application locally

# building the project
./mvnw clean verify

# running the app (port 8080)
./mvnw spring-boot:run 

The application exposes a dedicated POST /pinning endpoint, which causes thread pinning by blocking from within the synchronized block:

curl -X POST localhost:8080/pinning

Detected pinning should be logged like this:

2024-04-16T22:15:49.321+02:00  WARN 20226 --- [jfr-thread-pinning-spring-boot] [ Event Stream 1] m.j.p.JfrVirtualThreadPinnedEventHandler : Thread 'web-vt-5773efb7-e4f8-404a-8859-590b0ff1f1cb' pinned for: 254ms at 2024-04-16T22:15:48.974019792, stacktrace:
	java.lang.VirtualThread#parkOnCarrierThread: 675
	java.lang.VirtualThread#parkNanos: 634
	java.lang.VirtualThread#sleepNanos: 791
	java.lang.Thread#sleep: 507
	com.mikemybytes.jfr.pinning.ThreadPinningController#sleep: 36
	com.mikemybytes.jfr.pinning.ThreadPinningController#lambda$pinCarrierThread$0: 27
	com.mikemybytes.jfr.pinning.ThreadPinningController$$Lambda+0x000000c0014ec010.615676186#run: -1
	java.lang.Thread#runWith: 1596
	java.lang.VirtualThread#run: 309
	java.lang.VirtualThread$VThreadContinuation$1#run: 190
	jdk.internal.vm.Continuation#enter0: 320
	jdk.internal.vm.Continuation#enter: 312
	jdk.internal.vm.Continuation#enterSpecial: -1

Additionally, the duration of the recorded pinning events should be exposed as a timer in the /actuator/prometheus endpoint output:

(...)
# HELP jfr_thread_pinning_seconds_max  
# TYPE jfr_thread_pinning_seconds_max gauge
jfr_thread_pinning_seconds_max 0.25093325
# HELP jfr_thread_pinning_seconds  
# TYPE jfr_thread_pinning_seconds summary
jfr_thread_pinning_seconds_count 1.0
jfr_thread_pinning_seconds_sum 0.25093325
(...)

For more details, please refer to the original article Continuous monitoring of pinned threads with Spring Boot and JFR.