jfr.dcmd log is not shown

[Yasumasa Suenaga]

Hi all,

I tried to check arguments of -XX:StartFlightRecording via -Xlog:jfr+dcmd=debug , but I couldn't.

jfr.dcmd log will be shown from DCmdStart::execute, but I think it has two problems:

   1. Log level will be not set before showing log.
      LogTag::tagSetLevel is used to decide to show the log. But it will be set in
      JNI code which is called by JVM::<clinit>. JVM class is not loaded when
      DCmdStart::execute tries to show log.

   2. `settings` might be null, so NPE will occur when DCmdStart::execute tries to
      show log.

IMHO they can be fixed with following patch. Can I file this problem to JBS and send a webrev?
(I'm a Committer of jdk project)


---------------------
diff -r eadd0abbfdf4 src/jdk.jfr/share/classes/jdk/jfr/internal/dcmd/DCmdStart.java
--- a/src/jdk.jfr/share/classes/jdk/jfr/internal/dcmd/DCmdStart.java    Tue Oct 23 13:24:36 2018 +0200
+++ b/src/jdk.jfr/share/classes/jdk/jfr/internal/dcmd/DCmdStart.java    Wed Oct 24 00:10:05 2018 +0900
@@ -34,6 +34,7 @@
  import java.util.Arrays;
  import java.util.HashMap;
  import java.util.Map;
+import java.util.Objects;

  import jdk.jfr.FlightRecorder;
  import jdk.jfr.Recording;
@@ -81,9 +82,12 @@
       */
      @SuppressWarnings("resource")
      public String execute(String name, String[] settings, Long delay, Long duration, Boolean disk, String path, Long maxAge, Long maxSize, Boolean dumpOnExit, Boolean pathToGcRoots) throws DCmdException {
+        if (!JVM.getJVM().isAvailable()) {
+            throw new DCmdException("JFR is not available");
+        }
          if (LogTag.JFR_DCMD.shouldLog(LogLevel.DEBUG)) {
              Logger.log(LogTag.JFR_DCMD, LogLevel.DEBUG, "Executing DCmdStart: name=" + name +
-                    ", settings=" + Arrays.asList(settings) +
+                    ", settings=" + Arrays.asList(Objects.requireNonNullElse(settings, new String[0])) +
                      ", delay=" + delay +
                      ", duration=" + duration +
                      ", disk=" + disk+
---------------------


Thanks,

Yasumasa