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Java Flight Recorder is not reporting any File I/O events

One of the advertised features of Java Flight Recorder is the ability to report the file created, read or force in the File I/O tab in JMC 8.1

To test this feature, I created a small application that uses Apache commons-io to copy a large file from source to destination.

public static void fileCopy(String srcPath ,String destPath) throws IOException {
    File inpFile = new File(srcPath);
    if(inpFile.exists() && inpFile.isFile()) {
        File destFile = new File(destPath);
        FileUtils.copyFile(inpFile, destFile);
    }
}

On starting the FlightRecoder with the profile template, and observing the jfr file , I see no events in the File I/O template even though the copy operation took 11 seconds.

JVM used - OpenJDK 11 on Ubuntu.

Flight Recorder Screenshot

 java -XX:StartFlightRecording=name=benchmark,filename=benchmark.jfr,settings=profile -jar filecopyer-0.0.1-SNAPSHOT.jar

I also retried after changing the File IO threshold to 0 ns in the profile.jfc template, and still no events are recorded.

There are simply 0 events captured for jdk.FileWrite , jdk.FileRead and jdk.FileForce.

I however do see events under jdk.NativeMethodSample , which commons-io ends up calling.

Sample application on github : Profiled application

What am I doing wrong ?

Solution

  • Looks like the implementation of Files.copy, which Apache Commons seems to use, relies on async I/O to do the copying. See sun.nio.fs.UnixCopyFile::copy(...)

    JFR doesn't currently instrument async I/O operations.