Inspecting Java threads in Linux using top

You can inspect java threads with the tool jstack. It will list the names, stacktraces and other useful information of all threads belonging to the specified process pid.

Edit: The parameter nid in the thread dump of jstack is the hex version of the LWP that is displayed by top in the pid column for threads.

This might be a little old, but here's what I did to kinda merge top and jstack together. I used two scripts, but I'm sure it all could be done in one.

First, I save the output of top with the pids for my java threads into a file and save the jstack output into another file:

#!/bin/shtop -H -b -n 1 | grep java > /tmp/top.logjstack -l `ps fax | grep java | grep tomcat | sed "s/ *\([0-9]*\) .*/\1/g"` > /tmp/jstack.log

Then I use a perl script to call the bash script (called cpu-java.sh here) and kinda merge the two files (/tmp/top.log and /tmp/jstack.log):

#!/usr/bin/perlsystem("sh cpu-java.sh");open LOG, "/tmp/top.log" or die $!;print "PID\tCPU\tMem\tJStack Info\n";while ($l = <LOG>) {    $pid = $l;    $pid =~ s/root.*//g;    $pid =~ s/ *//g;    $hex_pid = sprintf("%#x", $pid);    @values = split(/\s{2,}/, $l);    $pct = $values[4];    $mem = $values[5];    open JSTACK, "/tmp/jstack.log" or die $!;       while ($j = <JSTACK>){        if ($j =~ /.*nid=.*/){            if ($j =~ /.*$hex_pid.*/){                $j =~ s/\n//;                $pid =~ s/\n//;                print $pid . "\t" . $pct . "\t" . $mem . "\t" .  $j . "\n";            }        }    }       close JSTACK;}close LOG;

The output helps me to find out which threads are hogging my cpu:

PID     CPU Mem JStack Info22460   0   8.0 "main" prio=10 tid=0x083cb800 nid=0x57bc runnable [0xb6acc000]22461   0   8.0 "GC task thread#0 (ParallelGC)" prio=10 tid=0x083d2c00 nid=0x57bd runnable 22462   0   8.0 "GC task thread#1 (ParallelGC)" prio=10 tid=0x083d4000 nid=0x57be runnable 22463   0   8.0 "GC task thread#2 (ParallelGC)" prio=10 tid=0x083d5800 nid=0x57bf runnable 22464   0   8.0 "GC task thread#3 (ParallelGC)" prio=10 tid=0x083d7000 nid=0x57c0 runnable...

Then I can go back to /tmp/jstack.log and take a look at the stack trace for the problematic thread and try to figure out what's going on from there. Of course this solution is platform-dependent, but it should work with most flavors of *nix and some tweaking here and there.

I have created a top-like command specifically for visualizing Java threads ordered by CPU usage and posted the source code at: https://github.com/jasta/jprocps. The command-line syntax is not nearly as rich as top, but it does support some of the same commands:

$ jtop -n 1

Sample output (showing ant and IntelliJ running):

  PID   TID USER       %CPU  %MEM  THREAD13480 13483 jasta      104   2.3   main13480 13497 jasta      86.3  2.3   C2 CompilerThread113480 13496 jasta      83.0  2.3   C2 CompilerThread0 4866  4953 jasta      1.0   13.4  AWT-EventQueue-1 12.1.4#IC-129.713, eap:false 4866 14154 jasta      0.9   13.4  ApplicationImpl pooled thread 36 4866  5219 jasta      0.8   13.4  JobScheduler pool 5/8

From this output, I can pull up the thread's stack trace in jconsole or jstack manually and figure out what's going on.

NOTE: jtop is written in Python and requires that jstack be installed.