© 2008 IBM Corporation IBM Java Technology Centre Exploring IBM Java 6 - New Features and...

© 2008 IBM Corporation

IBM Java Technology Centre

Exploring IBM Java 6 - New Features and Enhancements

Trent Gray-DonaldSenior Technical Staff Member –Java Virtual Machine

March 4, 2008


Java Overview | SE 6 Background and Update © 2008 IBM Corporation

Goal

Learn about IBM’s Java™ Virtual Machine (JVM™) offerings, see what’s improved technically on the way to Java platform v.6, and have a peek at some of our serviceability tools.

What’s in It for You?



Agenda

History and ArchitectureJava Platform v.6—What’s New This Release?

Java 5 platform updates

Java 6 class library updates

JVM Software

Garbage Collection

JIT

Shared Classes

Serviceability Update



Agenda




JVM Software

Garbage Collection

JIT

Shared Classes


5



IBM and Java

Java is critically important to IBM– As an fundamental infrastructure for our own software portfolio including

WebSphere and Rational products.

IBM is investing strategically in Java and in virtual machines– The transition to our next generation virtual machine base was completed

successfully in the Java SE 5.0 release.

– We expect to accelerate innovation in performance, reliability and serviceability going forward.

IBM is also looking to engender accelerated public innovation in Java

– Support of Eclipse, Apache (XML, Derby, Geronimo, Harmony, Tuscany, …)

– Broad participation in relevant open standards bodies such as JCP, OSGi

6



IBM’s Approach to Java Technology

ReferenceJava

Technology(Sun, OSS,

Others)

IBMJava

IBM JavaTechnology

Centre

Listen to and act upon market Listen to and act upon market requirementsrequirements

World class service and supportWorld class service and support Available on more platforms than any Available on more platforms than any

other Java implementationother Java implementation Highly optimizedHighly optimized Embedded in IBM’s middleware Embedded in IBM’s middleware

portfolio and available to ISV partnersportfolio and available to ISV partners

Quality EngineeringPerformance

SecurityReliability

Serviceability

Production RequirementsIBM Software Group

IBM eServerISVs

IBM Clients



Current offerings based on the J9 Virtual Machine– 3rd generation JVM software from IBM

– Designed from the ground up to be a scalable solution for embedded, desktop, and server class hardware

Common code base for all Java Platform, Micro Edition(Java ME platform) and Java Platform, Standard Edition(Java SE platform) products– Highly configurable—pluggable interfaces with different

implementations depending on the target market Class library independence Supports latest language features (Java SE v.6) Scaling to available hardware

– Wide range—“from a watch to a mainframe”

– Portable, configurable, flexible

Design Philosophy and Architecture



Pluggable components that dynamically load into the virtual machine Calls to

CLibraries

JavaSE 6

Operating System

NativeApplications

Java Application Code

OS-Specific Calls

Virtual Machine

Java SE 5

Garbage collector

Interpreter

Exception handler

Class loader

Thread Model

JVM Profiler

Debugger

Realtime Profiler

Port Library (file IO, sockets, memory allocation, etc.)

Uses 1 of many possible configurations

JCL Natives

JNI

CDCMIDP

Java calls

JNI

JIT

CLDCClass

Library

JNI = Java Native Interface



Agenda




JVM Software

Garbage Collection

JIT

Shared Classes


10



Java 5.0 Language Features Compile-Time Type Safety with Generics

– Similar to C++ templates– e.g. Vector<String>

Extended Syntax for for loops– Makes iterating over collections easier. Similar to for each in other languages.– void cancelAll(Collection<Tasks> tasks) { for (Task t : tasks)

t.cancel(); }

Auto-Boxing of Primitive Types– Automatic conversion of primitive types (e.g. int) to boxed equivalent (e.g. java.lang.Integer).

Typesafe Enumerations– An alternative to static, final constants. – e.g. enum Seasons { WINTER, SPRING, SUMMER, FALL}

Annotations: Language Metadata– Modifiers can be added to most language elements, and is available at runtime.– Allows semantic markup of programs for documentation, registration, etc.

Library enhancements for concurrency, management, JVMTI



Standard Java SE platform v.6 class library enhancements– java.util.concurrent updates (and lock monitoring)

– Collections framework

– Java.lang.instrument – class redefinition

Base JVM technology enhancements– JVM Tool Interface 1.1 (multiple agents,

better heap iterator API, instrumentation of native methods…)

– Class loading performance boost

– New class file data improves verification time

All that’s new…

Java Platform v.6

12



java.util.concurrent

Building scalable data structures is HARD… really hard!– Need to deeply understand concurrency and thread models.

– Low level hardware details dramatically affect performance

– Bugs are typically hard to shake out and irreproducible.

Java now provides very solid building blocks– Task scheduling (Executor framework)

– Concurrent collections (fast and scalable implementations of Map, List, Queue)

– Atomic variables (atomic math ops such as increment, test and set.)

– More variety in locking operations (tryEntry, multiple condvars)

Please use these libraries! (for everyone’s sanity.)

Great performance opportunities…

13



Testarossa JIT: Dynamic, adaptive, optimizing compiler

Dynamic– Triggered at runtime based on projected profitability of compilation– Compiled methods can be freely intermixed with interpreted callers/callees– May have multiple versions of methods built with different levels of optimization

Adaptive– Sensitive to need for program to have CPU (e.g. throttled during startup, runs on asynchronous

thread )– Able to profile program to retrieve common control paths or data values– Profile information used in subsequent re-optimizing compilation step

Optimizing– Comprehensive collection of conventional optimizations

– control flow simplification, data flow analysis– Speculative and Java-specific optimizations

– e.g.. devirtualization, partial inlining, lock coarsening– Tuned code generation for latest x86, Power, zArchitecture and more

– e.g.. instruction selection, instruction scheduling, register allocation



POWER 6® and IBM System z10™ exploitation Inliner and basic block layout improvements

– Determine what’s hot, what’s not (common path analysis)

Lock reservation (IBM paper at OOPSLA ’02)– Improves scaling and overall performance

Dozens of platform dependent and independent optimizations implemented, (e.g., new register allocators, live range reduction, idiom recognition)

Just In Time (JIT) Compiler updatesJava Platform v.6

15



-Xgcpolicy:optthruput (default)– My applications is designed around raw throughput and some GC pause is acceptable. – There is little intermingling of garbage collection and application work – better raw throughput.– The application is stopped each time garbage is collected.– Start here for tuning.

-Xgcpolicy:gencon– My application allocates many short-lived objects.– The heap space is fragmented.– My application is transaction-based (that is, objects in the transaction don't survive beyond the

transaction commit).

-Xgcpolicy:optavgpause– My application cannot tolerate the length of the GC pauses. A degradation in performance is

acceptable as long as the GC pause time is reduced.– I am running on a 64-bit platform and use a very large heap -- more than 3 or 4GB.– My application is a GUI application and I'm concerned about the user response times.

-Xgcpolicy:subpool • I have scalability problems on large multiprocessor machines.

Garbage Collector (GC) modesJava Platform v.6

16



Minor collection—takes place only in the young generation,normally done through direct copying => very efficient

Major collection—takes place in the new and old generation and uses the normal mark/sweep (+compact) algorithm

How the IBM J9 generational garbage collector works

IBM J9:

• Xmn (-Xmns/-Xmnx)

Sun:

• XX:NewSize=nn

• XX:MaxNewSize=nn

• Xmn<size>

Sun JVM Software Only:

• XX:MaxPermSize=nn

Nursery/Young Generation Old Generation Permanent Space

IBM J9:

• Xmo (-Xmos/-Xmox)

Sun:

• XX:NewRatio=n

Memory Management and Garbage Collection



Significantly faster classLoader load/unload performance and improved footprint Hierarchical Scanning—faster, memory hierarchy aware optimization for—

Xgcpolicy:gencon. Paper in ISMM ’06 (Siegwart and Hirtzel)

– Challenge: improving locality

– Commercial workloads spend 45% stalled in memory requests.– Copying GC can improve object ordering, co-locating

objects on the same page or cache line

– While maintaining scalability…

– Parallelism and workload balancing is essentialfor server workloads

Garbage Collector (GC) updatesJava Platform v.6

18



0%

5%

10%

15%

20%

25%

30%

1 2 3 4 5 6 7 8 9 10 11 12 13 1415 16 1718 19 20 2122 2324 2526

Scanned Slot to Copied Object Distance(Log2)

Pro

po

rtio

n

Breadth-FirstHierarchical

64 bytecache line

page size (4 kB) – less TLB misses, less L2 cache misses

(SPECjbb2005)

Parent-Child Distances for Hierarchical

19



Understanding Heap Sizes

occupied

free

-Xmx = max-Xms = initial

Hint: Use -verbose:sizes to see defaults for your platform, * denotes default

GC resizes heap based on occupancy and duration stats

Occupancy Constraint:30%* < free < 60%*

-Xminf < free < -Xmaxf

Duration Constraint:5%* < duration < 13%*

-Xmint < duration < -Xmaxt

Adjustment Size:1Mb* < adjustment < ∞*

-Xmine < adjustment < -Xmaxe

20



Garbage collection -Xgcpolicy:gencon changes

Removed 64mb cap on default new space size. Default maximum value of –Xmns and –Xmnx is now 25% heap. ONLY applies if you specify –Xgcpolicy:gencon

Allocate Space Survivor Old Generation

-XmnsAllocate Space SurvivorOld Generation Reserved but unallocated

-Xmns

-Xmnx

Startup state

Maximal state



Target: server environments where multiple JVM implementations exist on the same box

Goal: improve startup time and memory footprint Sharing of common data

– For classes, granularity is .class file

Multiple sharing strategies– Standard classloaders (including application Classloader) exploit the feature

when enabled

– API to extend custom ClassLoaders available

OverviewJava Platform v.6—Shared Classes

22



Shared Classes – details

Please attend Ben Corrie’s talk immediately following this one for many more details on what they are, how to use them, and when…

23



Customer Feedback Resulting in Process Changes

Java platform v.5 and before => closed beta program Java platform v.6 => open early access program Move to iterative development model



Agenda




JVM Software

Garbage Collection

JIT

Shared Classes


25



Reliability, Availability, and Serviceability

Centralization of tools

– Central customer visible repository of supported, maintained tools

– Extensible, open tools, with programmable extension interfaces Tools must be usable everywhere

– GUI mode for interactive use

– Report generation for headless environments Documentation

– Improvements to problem determination doc

– Aggregated search in IBM support assistant Iterate!

– Tools being deployed very regularly—looking for customer feedback

RAS strategy



IBM Support Assistant™

– Java platform 1.4.2, Java platform v.5, and Java platform v.6 plug-ins

Diagnostic Tool Framework For Java (DTFJ)– Presented at the 2006 JavaOneSM conference

DumpAnalyzer (using DTFJ)– First stop analysis engine for common Java problems (OutOfMemoryError and

crashes)

Garbage Collection and Memory Visualizer (GCMV)– Verbose GC visualization and analysis

Java Lock Analyzer (on alphaWorks)– Capture and visualize lock contention data.

Improvements across releasesReliability, Availability, and Serviceability

27



28



GCMV—Heap Usage Visualization

Heap occupancy

Pause times

29



GCMV—Comparison and Advice

Compare runs…

Performance advisor…

30



GCMV—Tuning Recommendations

31



Further Information

IBM JDK home page– http://www.ibm.com/developerworks/java/jdk/

IBM support assistant– http://www.ibm.com/software/support/isa/

Early access program– https://www14.software.ibm.com/iwm/web/cc/earlyprograms/ibm/java6/

WebSphere® Real Time™

– http://www-306.ibm.com/software/webservers/realtime/



Agenda Review




JVM Software

Garbage Collection

JIT

Shared Classes


© 2008 IBM Corporation


Questions & Answers

34



© IBM Corporation 2008. All Rights Reserved.

The workshops, sessions and materials have been prepared by IBM or the session speakers and reflect their own views. They are provided for informational purposes only, and are neither intended to, nor shall have the effect of being, legal or other guidance or advice to any participant. While efforts were made to verify the completeness and accuracy of the information contained in this presentation, it is provided AS IS without warranty of any kind, express or implied. IBM shall not be responsible for any damages arising

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