This documentation is for an old GraalVM version. See the latest version.

Build and Run Native Executables with JFR

JDK Flight Recorder (JFR) is a tool for collecting diagnostic and profiling data about a running Java application, built into the JVM. GraalVM Native Image supports JFR events and users can use the jdk.jfr.Event API with a similar experience to using JFR in the Java HotSpot VM.

To record JFR events when running a native executable, enable JFR support and JFR recording as described in this guide.

Note: JFR event recording is not yet supported on GraalVM JDK for Windows.

Enable JFR Support and Record Events at Run Time #

To build a native executable with the JFR events support, you first need to add the --enable-monitoring=jfr option when invoking the native-image tool. Then enable the system, start a recording, and configure logging at native executable run time:

-XX:+FlightRecorder: use to enable JFR at run time
-XX:StartFlightRecording: use to start a recording on application’s startup
-XX:FlightRecorderLogging: use to configure the log output for the JFR system

Follow the steps below to practice building a native executable with JFR support and recording events at run time.

Note: You are expected to have GraalVM installed with Native Image support. The easiest way to install GraalVM is to use the GraalVM JDK Downloader.

Install VisualVM by running:
```
 gu install visualvm
```

Save the following code to the file named JFRDemo.java.

 import jdk.jfr.Event;
 import jdk.jfr.Description;
 import jdk.jfr.Label;

 public class JFRDemo {

   @Label("Hello World")
   @Description("Build and run a native executable with JFR.")
   static class HelloWorldEvent extends Event {
       @Label("Message")
       String message;
   }

   public static void main(String... args) {
       HelloWorldEvent event = new HelloWorldEvent();
       event.message = "Hello, World!";
       event.commit();
   }
 }

This demo application consists of a simple class and JDK library classes. It creates an event, labelled with the @Label annotation from the jdk.jfr.* package. If you run this application, it will not print anything and just run that event.

Compile the Java file using the GraalVM JDK:
```
 $JAVA_HOME/bin/javac JFRDemo.java
```
It creates two class files: JFRDemo$HelloWorldEvent.class and JFRDemo.class.
Build a native executable with the VM inspection enabled:
```
 $JAVA_HOME/bin/native-image --enable-monitoring=jfr JFRDemo
```
The --enable-monitoring=jfr option enables features such as JFR that can be used to inspect the VM.
Run the executable and start recording:
```
 ./jfrdemo -XX:+FlightRecorder -XX:StartFlightRecording="filename=recording.jfr"
```
This command runs the application as a native executable. The -XX:StartFlightRecording option enable the built-in Flight Recorder and start recording to a specified binary file, recording.jfr.
Start VisualVM to view the contents of the recording file in a user-friendly way. GraalVM provides VisualVM in the core installation. To start the tool, run:
```
 $JAVA_HOME/bin/jvisualvm
```
Go to File, then Add JFR Snapshot, browse recording.jfr, and open the selected file. Confirm the display name and click OK. Once opened, there is a bunch of options you can check: Monitoring, Threads, Exceptions, etc., but you should be mostly interested in the events browsing. It will look something like this:

Alternatively, you can view the contents of the recording file in the console window by running this command:
```
 $JAVA_HOME/bin/jfr print recording.jfr
```
It prints all the events recorded by Flight Recorder.

Learn more about Native Image support for JFR events and how to further configure JFR recording and system logging.
Create and record your first event with Java.

Build and Run Native Executables with JFR

Enable JFR Support and Record Events at Run Time #

Related Documentation #

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