Td Mxc Java Troubleshooting Shin

Java Trouble-Shooting Sang Shin ● Sun Microsystems, Inc. ● javapassion.com ●

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Topics • JDK Debugging Tools • JPDA (Java Platform Debugger Architecture) architecture • Remote Debugging

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Performance, Debugging, Monitoring, Management, Code analysis, Testing Free online course http://javapassion.com/ javaperformance/ 3

JDK Debugging Tools

jps • List the JVMs that are currently running including embedded VMs > Associate a 'process number' with the running application

• jps

27798 Jps 25301 Main

• jps
-s

28029 sun.tools.jps.Jps 25301 org.netbeans.Main

• jps
-l 25301 Main -Djdk.home=/opt/java/javase/jdk1.6 -Dnetbeans.dirs=/opt/java/tools/netbeans6.0.1/nb6.0:/opt/java/tools/netbeans6.0.1/ide8:/opt/java/tools/netbeans-

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jinfo • List configuration information from a running VM or a core file > Information includes VM properties and command line

flags

• jinfo


Java System Properties: java.vendor = Sun Microsystems Inc. netbeans.user = /home/shulk/.netbeans/6.0 sun.java.launcher = SUN_STANDARD sun.management.compiler = HotSpot Client Compiler ... VM Flags: -Djdk.home=/opt/java/javase/jdk1.6 -Dnetbeans.dirs=/opt/java/tools/netbeans6.0.1/nb6.0:/opt/java/tools/netbeans-6.0.1/ide8:/opt/java/tools...

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jstat • List the statistics for a given VM > Class loading, GC on all spaces, hotspot compilation

• Provide a sample interval and the number of samples to take Process id

Interval

No. of sample

jstat -gcutil 25301 1000 10 S0 S1 E O P YGC YGCT FGC 73.79 0.00 81.32 42.10 99.56 1344 8.880 73.79 0.00 81.32 42.10 99.56 1344 8.880 73.79 0.00 81.32 42.10 99.56 1344 8.880

FGCT GCT 36 17.363 26.243 36 17.363 26.243 36 17.363 26.243

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jstack • Prints the stack traces of all the the threads attached to a virtual machine > Application thread, internal VM thread,

• Also performs deadlock detection with -l option • Use -F to force stack if VM is hung > Solaris and Linux only

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jstack – Sample Output

"Java Source Worker Thread" prio=10 tid=0x08267800 nid=0x63a5 waiting on condition [0x4532c000..0x4532d040] java.lang.Thread.State: TIMED_WAITING (parking) at sun.misc.Unsafe.park(Native Method) - parking to wait for <0x54b8d090> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject) at java.util.concurrent.locks.LockSupport.parkNanos(LockSupport.java:198) ... at java.util.concurrent.ThreadPoolExecuto$Worker.run(ThreadPoolExecutor.java:907) at java.lang.Thread.run(Thread.java:619) Locked ownable synchronizers: - <0x54b8cdd0> (a java.util.concurrent.locks.ReentrantLock$NonfairSync)

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jmap • Prints memory related statistics > Details the overall memory configuration > Details section on each of the space with capacity, free

and used

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jmap Sample Output (Solaris/Linux) Mark Sweep Compact GC Heap Configuration: MinHeapFreeRatio = 40 MaxHeapFreeRatio = 70 MaxHeapSize = 169869312 (162.0MB) NewSize = 1048576 (1.0MB) MaxNewSize = 4294901760 (4095.9375MB) OldSize = 4194304 (4.0MB) NewRatio = 12 SurvivorRatio = 8 PermSize = 33554432 (32.0MB) MaxPermSize = 209715200 (200.0MB) ... Eden Space: capacity = 6881280 (6.5625MB) used = 4437312 (4.23175048828125MB) free = 2443968 (2.33074951171875MB) 64.48381696428571% used

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jmap (Solaris/Linux)

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jmap (Windows)

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HPROF • Uses the JVMTI to get information from a Java VM • Data capture includes > CPU usages, heap dump, thread states

• Start at commandline > java
-Xrunhprof:
MyJavaApp

> Includes format=b for jhat analysis

• Useful options > heap=all – displays all heap info > cpu=sample – sample active thread

• Dump on application exit or CTRL-\ 14

jhat • Allows you to interactively work with a memory snapshot captured by jmap > Use jmap
-dump:format=b,file=heap_dump_file

• Use jhat to 'mount' heap file > Hosted on a web server > Access through a standard browser

• Shows the following (standard query) > > > >

All classes Object on the heap Instances Objects reachable from root set

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jhat Object Query Language • Develop custom query with object query language > SQL like, uses JavaScript for expression in from and where clause > A set of built-in functions like heap, referrers, reachables,

sizeof, etc.

• Use to answer questions like > Find all String instances that are over 1K in size select
s
from
j.l.Sring
s
where
s.count
>=
1024

> Find all URL instances that is referenced by 2 or more

objects

select
u
from
j.n.URL
u
where
count(referrers(u))
>
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Demo:

JDK Debugging Tools

http://www.javapassion.com/handsonlabs/javase6tools 17

Visual Tool - jconsole • Bundle with JDK > Graphical console that enables you monitor and manage

Java applications > API to create your own plugin to jconsole

• Provides information on > > > > >

Memory usage and GC activities Threads, thread stack trace, locks Objects pending finalization Runtime information such as uptime, CPU time JVM information such as classpath, properties, command line arguments, etc. 18

Visual Tool – visualvm • Open source project > Based on NetBeans platform, uses the update center > Current plugin includes VisualGC, jconsole, thread dump

analyzer, profiler > Runs only on JDK 6 and later > http://visualvm.dev.java.net

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Demo: VisualVM

http://www.javapassion.com/handsonlabs/javavisualvm 20

When to Use Them over NetBeans Profiler?

Usecases • Use jps to find which PID you want to dump • Use jmap to generate a heap dump that can be opened with the NetBeans profiler • Use OQL capability of jhat > Other features of jhat are now addressed by

HeapWalker

• Use jstack when full attach of the profiler is too much of a hassle > Useful in the field 22

Java Platform Debugger Architecture (JPDA)

Topics • What is JPDA? • JPDA architecture • Using JPDA

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What is JPDA?

What is JPDA? • Java Platform Debugger Architecture • JPDA is a multi-tiered debugging architecture • Allows tools developers to easily create debugger applications • Portable across platforms, virtual machine (VM) implementations and JDK versions.

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Goals of JPDA • To provide standard interfaces which allow Java programming language debugging tools to be easily written without regard to platform specifics such hardware, operating system and virtual machine implementation. • To describe a complete architecture for implementing these interfaces, including remote and cross-platform debugging. • To provide a reference implementation of this architecture. • To provide a highly modular architecture where the implementation and/or client of an interface can be different than the reference implementation or different from the JPDA component. 27

JPDA Architecture

JPDA Architecture

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JPDA Architecture • JVM TI (Java VM Tool Interface) > JVM TI is a new interface introduced in J2SE 5.0

which replaces JVMDI. > It defines the debugging services a VM provides.

• JDWP (Java Debug Wire Protocol) > Defines the communication between debuggee and

debugger processes.

• JDI (Java Debug Interface) > Defines a high-level Java language interface which

tool developers can easily use to write remote debugger applications.

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JPDA is Layered Architecture • Reference implementation includes > JVM TI implementations on multiple Sun VMs (see

VM documentation). > A back-end which uses JVM TI to implement the debuggee side of JDWP. > A front-end which uses the debugger side of JDWP to implement JDI. > Two simple example debugger applications which are built on JDI.

• Implementations may be substituted. 31

Using JPDA

Using JPDA • A debugger developer may hook into JPDA at any layer. • Since the JDI is the highest level and easiest to use we encourage developers to use this interface. > Example scenario: Suppose a company develops a

debugger using JDI. They can use it with the reference implementation and it will automatically work with the VMs and platforms Sun supports. It can also work, for example, with the reference implementation front-end and a debuggee running another company's VM that implements JDWP (which might use or by-pass JVM TI).

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Using JPDA (Continued..) • Some debuggers are built on top of lower layers, JDWP (for example if the front-end is not written in the Java language) or JVM TI (for specialized debuggers which need low-level functionality).

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Remote Debugging, Monitoring, Profiling, Managing 35

Topics • Remote debugging • Remote profiling • Remote monitoring & management

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Remote Debugging

Needs for Remote Debugging • Remote debugging is useful when you are developing an application that runs on a web server or on a different environment than the computer on which you are developing the application. • Debugging remote objects without remote debugging capability requires inserting a myriad of System.out.println( ) statements or other logging code. > Using logging code for debugging is slow and inefficient,

whereas using NetBeans for remote debugging is much more powerful.

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Remote Debugging via NetBeans • The NetBeans debugger can attach to a Java process already running in a separate JVM, either on the same computer or on a remote machine. • This gives a developer the same power for debugging remote applications and components running in Java-based server containers.

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Remote Debugging via NetBeans • Attaching to a remote JVM makes it possible to use breakpoints, conditionals, watches, and other debugging features with Java applications, applets, servlets, Enterprise JavaBeans, and RMI or CORBA server objects.

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How to build and run the target application • Sun's VM implementations require command line options to load the JDWP agent for debugging for the target application • On the computer where the application (debugee) is located, start the application in debugging mode. > JDK5 & JDK6: (Using new JVM TI interface) > -agentlib:jdwp=<sub-options> > Prior version of JDK5, JDK5 & JDK6 > -Xdebug > -Xrunjdwp:<sub-options> 41

<sub-options> • transport > is a method of communication between a debugger and the virtual

machine that is being debugged.

• address > when establishing a connection, transport addresses is used to

identify the end-point of the connection.

• server > if the server property is 'y', the application will listen for a debugger

to attach; otherwise, it will attach to the debugger at the specified address.

• suspend > if suspend is 'n', the application will start immediately and will not

wait for a debugger to attach to it. If 'y', the application will be

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How to build and run the target application: Example1 • -agentlib: jdwp=transport=dt_socket,server=y,address=8000 > Listen for a socket connection on port 8000. > Suspend this VM until attached (connected) by debugger

application (suspend=y by default). > Once the debugger application connects, it sends a JDWP command to resume the VM.

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How to build and run the target application: Example2 • -agentlib: jdwp=transport=dt_socket,server=y,address=localhost: 8000,timeout=5000 > Listen for a socket connection on port 8000 on the loopback

address only. > Terminate if the debugger does not attach within 5 seconds. > Suspend this VM until attached (connected) by debugger application (suspend=y by default). > Once the debugger application connects, it sends a JDWP command to resume the VM. 44

How to build and run the target application: Example3 • -agentlib: jdwp=transport=dt_shmem,server=y,suspend=n > Choose an available shared memory transport address and

print it to stdout. > Listen for a shared memory connection at that address. > Allow the VM to begin executing before the debugger application attaches.

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How to build and run the target application: Example4 • -agentlib: jdwp=transport=dt_socket,address=myhost:8000 > Attach to a running debugger application via socket on host

myhost at port 8000. > Suspend this VM until attached (connected) by debugger application (suspend=y by default).

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How to build and run the target application: Example5 • -agentlib: jdwp=transport=dt_socket,server=y,address=8000,ont hrow=java.io.IOException,launch=/usr/local/bin/debug stub > Wait for an instance of java.io.IOException to be thrown in > > > >

this VM. Suspend the VM (suspend=y by default). Listen for a socket connection on port 8000. Execute the following: "/usr/local/bin/debugstub dt_socket myhost:8000". This program can launch a debugger process in a separate window which will attach to this VM and begin debugging it.47

How to build and run the target application: Example6 • -agentlib: jdwp=transport=dt_shmem,server=y,onuncaught=y,lau nch=d:\bin\debugstub.exe > Wait for an uncaught exception to be thrown in this VM.

Suspend the VM. > Select a shared memory transport address and listen for a connection at that address. > Execute the following: "d:\bin\debugstub.exe dt_shmem

", where

is the selected shared memory address. > This program can launch a debugger process in a separate window which will attach to this VM and begin debugging 48 it.

Demo:

Remote Debugging

http://www.javapassion.com/handsonlabs/javadebugremote 49

Remote Profiling

Remote Profiling with NetBeans • You can profile an application that is running on a remote system such as a web server by attaching the profiler to the application. • When you use this mode, the remote application starts after the profiler is attached. > This mode enables you to obtain profiling data on the

startup of the target JVM.

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NetBeans Profiler Remote Pack • To attach profiler to an application on a remote system, you need to download and install the Profiler Remote Pack on the remote system. • The remote system needs to be started on the Profiler Remote Pack and configured to support remote profiling. • You can download the Profiler Remote Pack from the Profiler web site: > htttp://profiler.netbeans.org

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How to use Attach Wizard • You use the Attach Wizard to specify the attachment settings for your project. • In the Attach Wizard you specify the type of application and the remote location. • Based on the details that you provide, the Attach Wizard provides you with a set of instructions on how to configure the remote system to support profiling.

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How to use Attach Wizard • After configuring the remote system according to the instructions, you can attach the profiler to the remote location. > You only need to configure the attach mode once. > The attachment settings are associated with that project. > You can go through the Attach Wizard at any time to

change any of the attachment settings.

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Remote Monitoring & Management

JMX Architecture Remote Manager Application

JMX Agent

Manag es

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Tools Remote Monitoring and Management • JConsole • VisualVM (with JConsole plug-in) • jstat

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Java Trouble-Shooting Sang Shin ● Sun Microsystems, Inc. ● javapassion.com ●

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