Diagnosing Your Application on the JVM

Diagnosing Your
Application on the JVM
Staffan Larsen
Java SE Serviceability Architect
staffan.larsen@oracle.com
@stalar

The following is intended to outline our general product direction. It is intended
for information purposes only, and may not be incorporated into any contract.
It is not a commitment to deliver any material, code, or functionality, and should
not be relied upon in making purchasing decisions. The development, release,
and timing of any features or functionality described for Oracle s products
remains at the sole discretion of Oracle.

404 – Not Found
java.security.AccessControlException: access denied ("java.lang.management.ManagementPermission" "control")
at java.security.AccessControlContext.checkPermission(AccessControlContext.java:364)
at java.security.AccessController.checkPermission(AccessController.java:555)
at java.lang.SecurityManager.checkPermission(SecurityManager.java:549)
at oracle.jrockit.jfr.JFR.checkControl(JFR.java:43)
at oracle.jrockit.jfr.RepositoryChunk.<init>(RepositoryChunk.java:68)
at Demo$1.<init>(Demo.java:14)
at Demo.start(Demo.java:14)
at sun.applet.AppletPanel.run(AppletPanel.java:474)
at java.lang.Thread.run(Thread.java:722)

jcmd
jps
jvisualvm
jinfo
jmap
jstack
jstatd
JMX
perf counters
attach
jstat
serviceability agent
java flight recorder
java mission control

Copyright © 2012, Oracle and/or its affiliates. All rights reserved.7 Copyright © 2012, Oracle and/or its affiliates. All rights reserved.
Agenda §  Demos, walk-through
§  Internals
§  Future

Demo Recap
§  jps – list processes
§  jcmd – send Diagnostic Commands
–  VM.version
–  Thread.print
–  GC.class_histogram
–  GC.heap_dump
§  jstat – see performance counters
§  Java Mission Control
§  Java Flight Recorder

§  Internals
§  Future

Remote Access
§  JMX
–  jmc,
jvisualvm,
jconsole

–  Access information from java.lang.management MBeans
–  SSL and authentication
–  Enable startup: -‐Dcom.sun.management.jmxremote

–  Enable runtime: jcmd
ManagementAgent.start

§  jstatd

–  Daemon that runs on remote machine
–  jstat can connect to daemon

Discovery – what is running?
§  Well-known file for each JVM
–  <temp>/hsperfdata_<user>/<pid>

–  /tmp/hsperfdata_staffan/3636

§  Created on JVM startup
§  Deleted on JVM shutdown
§  Unused files deleted on startup

Java Discovery Protocol
§  Java process will broadcast presence
–  Every 5 seconds
§  Broadcast package contains
–  Main class name
–  Unique id
–  JMX service URL
-‐Dcom.sun.management.jmxremote.autodiscovery=true

jcmd
ManagementAgent.start
jdp.port=<port>

From freedigitalphotos.net/by digitalart
7u40

Attach – talking to the JVM
§  Allows sending “commands” for execution in the JVM
§  Receive text output
§  Local access by same user only
§  Used by jcmd,
jstack,
jmap,
jinfo

§  Mechanics differ on platforms

Attach: Linux / BSD / Solaris
§  Create file /tmp/.attach_pid<pid>

§  Send SIGQUIT to JVM
§  JVM looks for /tmp/.attach_pid<pid>

–  If not found a normal thread dump is done
§  JVM will create socket: /tmp/.java_pid<pid>

§  Use socket for communication
§  Solaris uses door API instead of sockets

Attach: Windows
§  Remote process injects code (!) into the JVM
–  VirtualAllocEx
/
WriteProcessMemory

§  Remote process creates a thread in the JVM to call the code
–  CreateRemoteThread

§  The code dynamically looks up JVM_EnqueueOperation() and calls it
§  Reads result from a pipe

Diagnostic Commands
§  Helper routines inside the JVM
§  Text output
§  Executed via the jcmd utility
–  soon JMX
§  Self-describing help facility
§  Different set of commands for different JVM versions
JDK 8

jvmstat / PerfCounter
§  /tmp/hsperfdata_staffan/3636

–  Contains a lot of run-time information about the JVM
§  Memory mapped file
§  Updated continuously by JVM
§  Use jstat to show information in readable form
§  Use "jcmd
PerfCounter.print" to see raw contents

Monitored JVM
attach
j*
JMX
jstat
RMI
JMX
client
JMX
attach
Mission Control
VisualVM
JConsole
jcmd
jstack
jmap
jinfo
Accessing the JVM
dcmd JVM
jvmstat
jstat(d)

Communicating with the JVM
Local access Remote access Two-way core files
attach ✔ ✔
jvmstat ✔
JMX ✔ ✔
jstatd ✔
SA ✔ (✔) ✔

attach JMX
jvmstat jstatd
RemoteLocal
Two-way
One-way
Communicating with the JVM

Serviceability Agent
§  For core-files or non-responsive JVMs
§  Uses debugger to read information
§  Last resort - suspends process in unknown state
jstack
<executable>
<core>

jstack
–F
<pid>

Monitored JVM
JVMj*
SA
jstack
jmap
jinfo
debugger
vmSymbols
Accessing the JVM

Java Flight Recorder
§  JVM-built-in profiler and tracer
§  Non-intrusive
§  Always-on
§  Captures both JVM and application data
–  GC, Locks, Compiler, Exceptions, CPU Usage, I/O, …
§  After-the-fact analysis
§  Circular buffers
New!
Photograph by Jeffrey Milstein
http://butdoesitfloat.com/In-the-presence-of-massive-gravitational-fields-this-perfect

JVM
JFR: How Is It Built?
§  Information gathering
–  Instrumentation calls all over the JVM
–  Application information via Java API
§  Collected in Thread Local buffers
⇢ Global Buffers ⇢Disk
§  Binary, proprietary file format
§  Managed via JMX
JFR
Thread
Buffers
Disk
JMX
GC RuntimeCompiler
Java API
Global
Buffers

Java Mission Control
§  Console
–  Online Monitoring and Management
–  MBean Browser
–  Triggers & Alerts
§  UI for Java Flight Recorder
$
bin/jmc

New!

§  Internals
§  Future

Future
§  More Diagnostic Commands (jcmd)
–  Eventually replacing jstack,
jmap,
jinfo

§  JMX Enhancements
–  Annotations, REST protocol, batched updates
§  Improved Logging for the JVM
–  JEP 158
§  Remove JConsole, hprof agent, jhat (?)
It’s soon here!

Take-away
§  Know which tools exists
§  Seen the tools in use
§  Something new and something useful
§  Go and experiment with the tools!
@stalar
serviceability-dev@openjdk.java.net

More Sessions
§  Oracle Java Mission Control: Java Flight Recorder Deep Dive
–  Tutorial
–  Today 10 am – 12 pm
§  Java Flight Recorder Behind The Scenes
–  Session
–  Wednesday 11:30 am – 12:30 pm

@stalar
serviceability-dev@openjdk.java.net

Diagnosing Your Application on the JVM

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