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

jhat jstat
jmap
jps jstack
VisualVM
Eclipse
TPTP MAT

TOD jstatd

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

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

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

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

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

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

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

Your favorite
Open Source Debugging Tool?

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

I’ve got the only tool I need

jmap -dump:ﬁle=myﬁle.hprof <pid>

java -XX:+HeapDumpOnOutOfMemoryError MyApp

jinfo -ﬂag +HeapDumpOnOutMemoryError <pid>

OutOfMemoryError
Drive in to office!

jhat -J-Xmx512m <yourdump.hprof>

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[]

Shallow Heap

java.util.HashMap



Retained Heap

java.util.HashMap



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

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="/.*/")
)
())));
}

@OnMethod(
clazz="/.*/",
method="println"
)
public static void m2(AnyType[] args) {
())));
}

/**
* ONEXIT TRACEPOINT. CALLED WHEN A BTRACE METHOD CALLS EXIT(INT).

)
())));
}

@OnMethod(
clazz="/.*/",
method="println"
)
())));
}

/**
*/
@OnExit
public static void onexit(int code) {
println("****** THE BTRACE PROGRAM IS EXITING.");
}

/**
* LOW MEMORY TRACE POINT.
*/
@OnLowMemory(
pool = "Tenured Gen",
threshold=58720250

())));
}

/**
*/
@OnExit
}

/**
*/
@OnLowMemory(
threshold=58720250
)
public static void onLowMem(MemoryUsage mu) {
println("******");
println(mu);
}

/**
* MEMORY HISTOGRAM TRACE POINT.
*/
private static Map<String, AtomicInteger> histo = newHashMap();

/**
*/
@OnExit
}

/**
*/
@OnLowMemory(
threshold=58720250
)
println("******");
println(mu);
}

/**
*/

@OnTimer(4000)
public static void print() {
if (size(histo) != 0) {
printNumberMap(strcat("******", "Component Histogram"), histo);
}
}
}

*/
@OnLowMemory(
threshold=58720250
)
println("******");
println(mu);
}

/**
*/

@OnTimer(4000)
public static void print() {
if (size(histo) != 0) {
printNumberMap(strcat("******", "Component Histogram"), histo);
}
}
}

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.

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

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

Goal:
Comprehend the application
runtime call sequence better.

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

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

Eclipse TPTP

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

ancient weapons are no match...

bring a better weapon to the ﬁght

You work the weekend solving it.

Matthew McCullough

May the debugging force be with you.

Matthew McCullough

Than ks in advance for
your complete d evals!

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/

Open Source Debugging for Java 1.4.0

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Open Source Debugging for Java 1.4.0