s109 cics-java

CICS Java – Beauty and the Beast

Ian Burnett

CICS - S109

© 2015 IBM Corporation CICS Java – Beauty and the Beast – S109

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Agenda


Java: An Overview


A Brief History of Programming Languages

FORTRAN

COBOL

PL/I

C

C++

Oak Java

Smalltalk

Lisp

ALGOL


What is Java and what makes it different?

Java is What makes Java different Java is NOT compiled to executable code, it is

compiled to bytecode that runs in a virtual machine The virtual machine uses the just-in-time compiler

(JIT) to execute the code Java is not based on programs, it is based on classes Java uses a garbage collector, that removes unused

objects from the storage Java development is often based on existing

programming patterns (Design Patterns) Encourages loose coupling between components Most of the build in funtionality of Java is based of

class libraries, that are build in the Java Runtime (JRE)

Java contains a library for user interface development Java has the ability to reflect about the runtime with

several methods Java has type-safe variable declaration Uses JNI for native system calls and JDBC for

database calls

Java is Object-oriented Platform-independent Broadly-supported and prevalent A state-of-the-art language [and an island in Indonesia] Something YOU should care about

Java is not Something new and unreliable An error-prone language The only solution for good code Independent on its own Something that only the distributed world should

care about Easy to write or fully-performant out of the box A composable workbox full of libraries


Traditional Applications


Executing a COBOL Program in CICS

•Load the program into storage from DASD

•Initialise a new Language Environment enclaveo ... ?


Language Environment (LE)

•Prior to LE, all languages brought their own runtime libraries

•Why now LE?


Executing a COBOL Program in CICS

•Load the program into storage from DASD

•Initialise a new Language Environment enclave

•Control is given to the application code

•Once the application ends it 'returns' to LE


Enclave Structure Within CICS

= CICS Region

= CICS initial transaction

= Main Transaction Programor EC LINKed Program


Storage in LE


Dispatching a Program in CICS

CIC

S A

/S

z/OSDispatcher

WEB WEB WEB WEB

GlobalSRB

TCB

ASCBTCB

OTETCB

OTE

WEB

TCBQR

CICSDispatcher

DFHSIP

LE Enclave

Application code


Anatomy of a Java Application


jar file

Java package

Java packaging and hierarchy

•Classes contain data and logic

•Packages contain these classes and organize them

•Jar files contain the classes and are the base for applications and libraries

•At the runtime, there are just a lot of classes on a classpath

Java package

class files

Java package

class files

class files


The Java Virtual Machine

•Java Virtual Machine (JVM)

•Run time data management is performed by the JVM

•The JVM will only stop if the last non-daemon thread finishes

•Platform-independence means that:o Java is never compiled to machine instructions upfronto Everything in Java is abstracted (including data types)


Java Runtime

JVM

OS and Hardware

Nat

ive

codeRuntime Libraries

Java Application


Bytecode and the JIT Compiler


Java Bytecode

•Developer writes application in Java

•Compiler converts to bytecode

•Bytecode is stored in jar files on disk

•JVM loads bytecode from disk

•... ?


Loading a Java Class

•Loading

•Linkingo Verifyingo Preparingo Resolving

•Initialising


Classpath and OSGi

Java VM

log4j

barcode4j

axis

batik

commons

derby

fop

ezmorph

freemarker

httpunit

jakarta

jcl

json

jdbm

jdom

jenks

jpos18

jython

looks

lucene

mail

mx4j

naming

jetty

poi

resolver

rome

serializer

servlets

tomcat

velocity

ws-commons

xalan

wsdl4j

xerces

xmlgraphics

xmlrpc

xmlapis

...

geronimo

bsh

bsf

guiapp

hhfacility

manufact.

marketing

minerva

accounting

assetmaint

base

bi

catalina

common

oagis

order

ebay

content

datafile

ecommerce

entity

googlebase

ofbiz

widget

minilang

party

pos.

product

workeffort

workflow

...

sunjce_prov.

plugin

jsse

jce

rt

dnsns

...

...ClassNot

FoundException

BeginHere


Comparing Java and bytecode

public int sum(int a, int b){ int result = 0; result = a + b; return result;}

public int sum(int, int); Code: 0: iconst_0 1: istore_3 2: iload_1 3: iload_2 4: iadd 5: istore_3 6: iload_3 7: ireturn


Executing Bytecode

•The JVM constructs for each Thread an execution engine

•In this engine the application now needs to be executed

•Interpreting bytecode is slow


Just In Time Compiler (JIT)

Java Application

JVM JIT

CompilerJ9

Interpreter

OS and Hardware


JIT Operation

•Sampling process

•Multiple levels of optimisation

•Transparent to application and to CICS region


Java on z/OS


Differences on z/OS

IBM JDK for z/OS

Standard JSE(JDK specification)

z/OS Extensions

Just In Time Compiler (JIT)Exploitation of the Hardware Architecture

z/OS Operating System and System z Hardware


An LE Enclave With Java


Recap: Dispatching a Program in CICS

CIC

S A

/S

z/OSDispatcher

WEB WEB WEB WEB

GlobalSRB

TCB

ASCBTCB

OTETCB

OTE

WEB

TCBQR

CICSDispatcher

DFHSIP

LE Enclave

Application code


Dispatching a Java Program in CICS

CIC

S A

/S

z/OSDispatcher

WEB WEB WEB WEB

GlobalSRB

TCB

ASCBT8 TCB T8 TCB

Enclave

WEB

TCBQR

CICSDispatcher

DFHSIP

LE Enclave

Application code

pthread

pthread

GC

JIT

JVM server


Garbage Collection

•All memory management is responsibility of JVM

•Periodically performs garbage collectiono Many approacheso Recommend using -Xgcpolicy:gencon for OLTP

•New objects created in the nursery area

•As objects age they are moved to the tenured area


Shared Classes

•Faster JVM start

•Faster application start

•Reduced memory consumption for multiple JVMs


Compressed References

•-Xcompressedrefs


Comparing COBOL and Java


Comparing COBOL to Java

Develop a COBOL program

Cobol does not know complex data types or objects Data elements are usually shared, not hidden The compile is performed done after coding (no

online syntax checking) Compiler performs fewer static tests Debugging is performed in multiuser environments Pointers to storage locations

Runtime Behaviour of Cobol

LE does not check whether the loaded program is corrupt

The runtime can not check whether the data is assigned correctly and Problems can arise

Handlers get control if something went wrong Memory is defined upfront

Develop a Java program

Data is structured in complex objects Variables are not shared, they are addressed by

methods of the object Compiles are executed every time a class is saved

(while ongoing syntax check is performed) Compiler performs a lot of static testing Debugging is usually performed locally Memory can NEVER be addressed directly

Runtime Behaviour of Java

The JVM checks the bytecode after loading the class Classes are checked during compilation and in

runtime data is only assigned if types match Classes and methods can throw exceptions if a

problem occurs New objects can be generated dynamically


Updating Programs – COBOL and Java

Update a COBOL Program in CICS

COBOL program is compiled/linked into a PDSe that is concatenated into the RPL upfront of the existing load library or to replace the existing version

In CICS issue a NEWCOPY or PHASEIN to let CICS reload the program from the dataset

Use the new program

Update a Java Program in CICS

In Java you can't replace runtime code Frameworks like OSGi enables the exchange of

bundles You need to decouple the application design (using

micro services in OSGi or accept a small outage

Problems with this Approach

Compatibility is a contract that is not checked until runtime

The connection is something the compiler is not aware of

Problems with this Approach

The simple PHASEIN or NEWCOPY is not possible A complex build infrastructure is necessary Only bundles/services, not classes can be “phased

in” A change in application development architecture is

necessary


Specialty Engines


zAAP

•IBM System z Application Assist Processor

•Provides dedicated environment for execution of Java workloads and parsing of XML

•Available on:o zEnterprise EC12 / BC12o zEnterprise 196 / 114o System z10o System z9

•Superseded by zIIP on IBM z13


zIIP

•IBM System z Integrated Information Processor

•Many IBM products exploit zIIP engines

•No IBM software charges on zAAP / zIIP capacity

•Available on all System z machines since System z9

•From z/OS 1.11: zAAP-on-zIIP

•Specialty engines always run full speedo Even on subcapacity machines


Moving Eligible Work to a zIIP

Eligiblework

Eligiblework

Eligiblework

Eligiblework

Eligiblework

Eligiblework

GCP zIIPGCP


Specialty Engines and the z/OS Dispatcher

GCP zAAP

CICSStart Java application

JVMMark as zAAP-eligible

z/OS DispatcherSuspend TCB on GCP

z/OS DispatcherDispatch TCB on zAAP

JVMExecution of byte code

JVMMark as zAAP-ineligible

z/OS DispatcherSuspend TCB on zAAP

z/OS DispatcherDispatch TCB on GCP

JVMReturn to CICS

CICSSubsystem code


Questions?

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