1 Reply Latest reply on Jun 21, 2014 6:57 PM by Staffan Larsen-Oracle

    How to match the JVM thread id with Linux TOP

    Alessandro I

      For learning purposes I am trying to correlate the native thread id from linux os with a java thread dump taken with jstack utility.

      The problem is I cannot find any matching nid into the dump file. I have tried with 2 different JVMs:

      1. JRockit only prints the following header informations

        "RMI TCP Accept-7099" id=17 idx=0x5c tid=6594 prio=5 alive, in native, daemon

      2. While on another standalone Sun JVM process on the same machine I have

        RMI TCP Accept-0" daemon prio=10 tid=0x8f359000 nid=0x16b5 runnable [0x884ad000]

      As far as I know the only way to match the thread from a TOP command is to use the nid
      Well, in JRockit I'd like to know how to achieve the same goal as I can't see that header, but even with the Sun JVM, if I try to lookup the thread ID in an hexadecimal value I don't always find it, which makes me think the approach is not completely correct.

      Here is what I am doing:

      1. take a dump of the java processI am interested.

        jstack 6567 >> /tmp/jstack.example

      2. then I take a look with TOP at which thread is taking majority of the CPU.

        top -Hu myUsr

        7324 oracle 20 0 2558m 1.4g 3292 S 1 17.6 0:10.21 RMI TCP Connect
        6553 oracle 24 4 1134m 72m 1912 S 1 0.9 0:57.22 (VM Periodic Ta
        6587 oracle 20 0 2558m 1.4g 3292 S 0 17.6 0:05.37 VM JFR Buffer T
        6603 oracle 20 0 2558m 1.4g 3292 S 0 17.6 0:14.87 ExecuteThread: \

      3. I am interested on the first line so I convert the PID id in an hexadecimal value using

        printf "%x\n" 7324

      The output is 1c9c

      Now if I look at the dump file I cannot find any matching ID. Am I doing any thing wrong here? Thanks