Open Source Debugging for Java 1.4.0

Open Source Java Debugging Tools by Matthew McCullough of Ambient Ideas, LLC

Code Examples http://github.com/matthewmccullough Twitter @matthewmccull Email matthewm@ambientideas.com Blog http://www.ambientideas.com/blog sidebar has my social networking proﬁle links

http://delicious.com/matthew.mccullough/opensource+debugging

Ins tead

jhat jstat jmap jps jstack VisualVM Eclipse TPTP MAT TOD jstatd

Hotspot JVMs

jps process list

What JVM options did we use when we started up the app server?

jps -l Sh ow fu ll pa ck ag e na m e

Sh ow jps -l -v Sh fu ow ll pa JV ck M ag e ar gu nam m e en ts

Sh ow Sh fu ow ll pa JV ck M ag jps -l -v -m e Sh ar ow gu nam m e m en ts ain () ar gu m en ts

VIDEO JPS

only local?

jps 10.15.25.32

Run jstatd daemon

Allow-all policy

y lic Po ur Yo jstatd -J-Djava.security.policy=allowall.pol

grant codebase "file:${java.home}/../lib/tools.jar" { permission java.security.AllPermission; };

grant codebase "file:${java.home}/../lib/tools.jar" { permission java.net.SocketPermission "<YourDesktopHostnameOrIP>:1099", "accept, connect, listen, resolve"; };

let’s start up the jstatd daemon

VIDEO JSTATD

jps 10.15.25.32

Windows let’s run JPS from across the network to a Mac

VIDEO JPS REMOTE

jstat process info

Sh ow ga rb ag e jstat -gcutil <pid> co lle ct io n

es pl m sa n ee ns tw io tit be pe s re m jstat -gcutil <pid> 500 999

es lin X y er ev r e ad he ow Sh jstat -gcutil -h5 <pid> 500 999

VIDEO JSTAT REMOTE

jstack stack dumps

jstack <pid>

jstack -F <pid>

of in ck lo e os rb Ve jstack -l <pid>

Direct this output to a ﬁle with a tdump extension Use TDA on VisualVM to analyze it

javap class file disassembler

We added a new method to a class. Is it on the server-deployed copy of the app?

javap classﬁle

e os rb Ve javap -v classﬁle

major version: 48 = Java 1.4 major version: 49 = Java 5 major version: 50 = Java 6

In te rn al ty pe javap -s classﬁle si gn at ur es

ds ho et m te iva Pr ow Sh javap -private classﬁle

Survey

StackOverﬂow.com

Your favorite Open Source Debugging Tool?

❸ VisualVM

❷ Eclipse

❶ System.out.println(brokenobj) System.out.println(broke System.out.println(brokenobj); nobj) System.out.println(brokenobj); System.out.p rintln(brokenobj); System.out.pr intln(brokenobj); System.out.println(brokenobj); System.out.println(brokenobj); System.out.println(brokenobj); System.out.println(brokenobj); ystem.out.println(broken obj); System.out.println(brokenob System.out.println(brokenobj); System.out.p rintln(brokenobj) System.out.println(brokenobj);

I’ve got the only tool I need

jmap memory maps

jmap histogram

jmap -histo <pid>

jmap -histo:live <pid>

jmap heap dump

jmap -dump:ﬁle=myﬁle.hprof <pid>

java -XX:+HeapDumpOnOutOfMemoryError MyApp

jinfo -ﬂag +HeapDumpOnOutMemoryError <pid>

OutOfMemoryError Drive in to office!

jhat heap analysis

jhat -J-Xmx512m <yourdump.hprof>

http://localhost:7000

select z from java.lang.String z

select z from java.lang.String z where z.count >= 50

http://blogs.sun.com/sundararajan/date/200509

eclipse memory analyzer M.A.T.

EclipseMemoryAnalyzer Purpose Investigate memory usage. Useful for Visualizing memory footprint. Finding memory leaks. Querying through (OQL) allocated memory. Discovering heavy memory allocation sources.

EclipseMemoryAnalyzer Gotcha Doesn’t create heap dumps, just analyzes. Available as a plugin or standalone RCP app.

java.util.HashMap java.lang.String java.lang.String java.lang.String char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[]

Shallow Heap java.util.HashMap java.lang.String java.lang.String java.lang.String char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[]

Retained Heap java.util.HashMap java.lang.String java.lang.String java.lang.String char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[] char[]

Load a heap dump in MAT

VIDEO ECLIPSE MAT

Run some OQL on it

VIDEO ECLIPSE MAT OQL

btrace

Can you put a few debugging “sysouts” into that running production app?

BTrace Tracing

BTrace Tracing Production-time Operates on deployed code Uses debugging hooks to re-deploy class ﬁles Runtime injection of tracing statements

BTrace Tracing Code Tracing scripts written in Java. Limited to a catalog of static methods. Compiled at design time or tracing time. Unsafe mode

import com.sun.btrace.annotations.*; import static com.sun.btrace.BTraceUtils.*; import com.sun.btrace.AnyType; import java.lang.management.MemoryUsage; import java.util.concurrent.atomic.AtomicInteger; import java.util.Map; @BTrace public class TraceAllMethodCalls { /** * METHOD CALL TRACEPOINT. */ @OnMethod( clazz="com.ambientideas.HelloWorldJava", method="print", location=@Location(value=Kind.CALL, clazz="/.*/", method="/.*/") ) public static void m(AnyType[] args) { //System.out.println("Hello"); println(strcat("****** WE'VE ENTERED A METHOD ON CLASS: ", name(probeClass ()))); println(strcat("****** WE'VE ENTERED METHOD: ", probeMethod())); } @OnMethod( clazz="/.*/",

import java.lang.management.MemoryUsage; import java.util.concurrent.atomic.AtomicInteger; import java.util.Map; @BTrace public class TraceAllMethodCalls { /** * METHOD CALL TRACEPOINT. */ @OnMethod( clazz="com.ambientideas.HelloWorldJava", method="print", location=@Location(value=Kind.CALL, clazz="/.*/", method="/.*/") ) public static void m(AnyType[] args) { //System.out.println("Hello"); println(strcat("****** WE'VE ENTERED A METHOD ON CLASS: ", name(probeClass ()))); println(strcat("****** WE'VE ENTERED METHOD: ", probeMethod())); } @OnMethod( clazz="/.*/", method="println" ) public static void m2(AnyType[] args) { println(strcat("****** WE'VE ENTERED A METHOD ON CLASS: ", name(probeClass ()))); println(strcat("****** WE'VE ENTERED METHOD: ", probeMethod())); } /** * ONEXIT TRACEPOINT. CALLED WHEN A BTRACE METHOD CALLS EXIT(INT).

) public static void m(AnyType[] args) { //System.out.println("Hello"); println(strcat("****** WE'VE ENTERED A METHOD ON CLASS: ", name(probeClass ()))); println(strcat("****** WE'VE ENTERED METHOD: ", probeMethod())); } @OnMethod( clazz="/.*/", method="println" ) public static void m2(AnyType[] args) { println(strcat("****** WE'VE ENTERED A METHOD ON CLASS: ", name(probeClass ()))); println(strcat("****** WE'VE ENTERED METHOD: ", probeMethod())); } /** * ONEXIT TRACEPOINT. CALLED WHEN A BTRACE METHOD CALLS EXIT(INT). */ @OnExit public static void onexit(int code) { println("****** THE BTRACE PROGRAM IS EXITING."); } /** * LOW MEMORY TRACE POINT. */ @OnLowMemory( pool = "Tenured Gen", threshold=58720250

public static void m2(AnyType[] args) { println(strcat("****** WE'VE ENTERED A METHOD ON CLASS: ", name(probeClass ()))); println(strcat("****** WE'VE ENTERED METHOD: ", probeMethod())); } /** * ONEXIT TRACEPOINT. CALLED WHEN A BTRACE METHOD CALLS EXIT(INT). */ @OnExit public static void onexit(int code) { println("****** THE BTRACE PROGRAM IS EXITING."); } /** * LOW MEMORY TRACE POINT. */ @OnLowMemory( pool = "Tenured Gen", threshold=58720250 ) public static void onLowMem(MemoryUsage mu) { println("******"); println(mu); } /** * MEMORY HISTOGRAM TRACE POINT. */ private static Map<String, AtomicInteger> histo = newHashMap();

/** * ONEXIT TRACEPOINT. CALLED WHEN A BTRACE METHOD CALLS EXIT(INT). */ @OnExit public static void onexit(int code) { println("****** THE BTRACE PROGRAM IS EXITING."); } /** * LOW MEMORY TRACE POINT. */ @OnLowMemory( pool = "Tenured Gen", threshold=58720250 ) public static void onLowMem(MemoryUsage mu) { println("******"); println(mu); } /** * MEMORY HISTOGRAM TRACE POINT. */ private static Map<String, AtomicInteger> histo = newHashMap(); @OnTimer(4000) public static void print() { if (size(histo) != 0) { printNumberMap(strcat("******", "Component Histogram"), histo); } } }

* LOW MEMORY TRACE POINT. */ @OnLowMemory( pool = "Tenured Gen", threshold=58720250 ) public static void onLowMem(MemoryUsage mu) { println("******"); println(mu); } /** * MEMORY HISTOGRAM TRACE POINT. */ private static Map<String, AtomicInteger> histo = newHashMap(); @OnTimer(4000) public static void print() { if (size(histo) != 0) { printNumberMap(strcat("******", "Component Histogram"), histo); } } }

visualvm

Useful for ‣ Discovering the GC cycles of your app. ‣ Finding the largest memory usage culprits. ‣ Difﬁng memory snapshots. ‣ Injecting btrace code. ‣ Snapping heapdumps.

Gotcha Download version 1.2 even if your JDK includes 1.0. Standalone version always ahead of JVM version.

VisualVM in action

BTrace in action

omniscient debuggers

Luke, you can destroy the bug! He has foreseen this. It is your destiny.

TOD (by Guillaume Pothier)

TOD ✴ Eclipse-integrated omniscient debugger ✴ observe all memory changes ✴ execute once, review inﬁnitely ✴ rewind and step through call stacks, loops ✴ Windows-only (DLL)

VIDEO TOD

comprehension tools

Goal: Comprehend the application runtime call sequence better.

amida http://sel.ist.osaka-u.ac.jp/~ishio/amida/

jtracert

jtracert http://code.google.com/p/jtracert/

Eclipse TPTP

Eclipse TPTP ✴ proﬁle an application’s performance ✴ render call sequence diagrams ✴ almost ready for Mac OS

VIDEO TPTP

decompiling tools

JD-Eclipse

System.out.println()

ancient weapons are no match...

bring a better weapon to the ﬁght

if a bug strikes you down...

You work the weekend solving it.

Matthew McCullough matthewm@ambientideas.com

May the debugging force be with you. Matthew McCullough matthewm@ambientideas.com

Than ks in advance for your complete d evals!

Code Examples http://github.com/matthewmccullough Twitter @matthewmccull Email matthewm@ambientideas.com Blog http://www.ambientideas.com/blog sidebar has my social networking proﬁle links

Resources Eclipse Memory Analyzer http://www.eclipse.org/mat/ VisualVM https://visualvm.dev.java.net/ GCHisto https://gchisto.dev.java.net/ BTrace https://btrace.dev.java.net/ DTrace, XRay, Instruments http://en.wikipedia.org/wiki/DTrace

Resources TOD http://pleiad.cl/tod/ JTracert http://code.google.com/p/jtracert/ Amida http://sel.ist.osaka-u.ac.jp/~ishio/amida/ TPTP http://www.eclipse.org/tptp/ JD-Eclipse http://java.decompiler.free.fr/

Image Credits ‣ http://www.ambientideasphotography.com ‣ http://upload.wikimedia.org/wikipedia/commons/a/a4/ BernardMadoff.jpg ‣ http://flickr.com/photos/triller/2226679393/ ‣ http://flickr.com/photos/ektogamat/2687444500/ ‣ http://flickr.com/photos/bfionline/2380398799/ ‣ http://flickr.com/photos/symphoney/76513801/ ‣ http://flickr.com/photos/foxypar4/2124673642/ ‣ http://flickr.com/photos/morberg/3146874095/ ‣ http://flickr.com/photos/triller/2226679393/

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Open Source Debugging for Java 1.4.0

by Matthew McCullough on Mar 11, 2010

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Open Source Debugging for Java 1.4.0 — Presentation Transcript