Java is a new language on the mainframe

FOR MORE INFORMATION PLEASE CONTACTXact Consulting A/SArnold Nielsens Boulevard 68ADK-2650 Hvidovre

+45 7023 [email protected]

Enterprise Modernization

Java is a new Languageon the Mainframe

Copenhagen, 8th January 2016

Michael Erichsen,Xact Consulting A/S,

[email protected]

Agenda

• Why Java on z?• Which kind of language is Java?• How is Java implemented on z?• How do I develop mixed language Java applications on z?• What is the security setup?• What do I need to learn?

Second Slot after Lunch?This is surely the Graveyard Shift!

• What do you think System.exit() will do?

• What do you think it will do in CICS?

Second Slot after Lunch?This is surely the Graveyard Shift!

• Exactly the same as aCOBOL STOP RUN in CICS!

System.exit() in CICS13.16.28 STC00106 +DFHSJ0214 CICSTS51 01913:16:28 CICSTS51 A class in a JVM Server has invoked System.exit(). CICS will shut down immediately.13.16.28 STC00106 +DFHDU0201 CICSTS51 ABOUT TO TAKE SDUMP. DUMPCODE: ASJS , DUMPID: 1/002313.16.50 STC00106 +DFHTM1703 CICSTS51 CICS is being terminated by userid CICSUSER in transaction HT01 at netname SC0TCP29.13.16.50 STC00106 +DFHMQ0410 I 01/05/2016 13:16:50 CICSTS51 CICS immediate shutdown detected. Adapter terminated.13.16.52 STC00106 BPXP018I THREAD 1F8EBC0000000000, IN PROCESS 67174429, ENDED WITHOUT BEING UNDUBBED WITH COMPLETION CODE 0033E000, AND REASON CODE 00000000.…13.17.03 STC00106 +DFHDU0303I CICSTS51 Transaction Dump Data set DFHDMPA closed.13.17.03 STC00106 +DFHKE1799 CICSTS51 TERMINATION OF CICS IS COMPLETE.13.17.12 STC00106 $HASP395 CICSTS51 ENDED




Why Java on z?

Java on the Big Iron

• Open the mainframe to a new generation of developers• Portability of applications• Wide choice of open and closed source packages• Typical use: Non-mixed, Java only– E.g. in WebSphere, batch, CICS, IMS, or DB2 Stored procedures

COBOL and PL/I are Native to the Mainframe

Java is also NativeIt was just born later

10

Old or New?

• OO is just a way to do some categories of computing– Not something given to Moses on tablets

• The first OO language, Simula, was formalized in 1962-1965– Last version 1986– Latest Java version 8: 2014

• COBOL was formalized in 1959-60– Latest ISO standard: COBOL 2014 – Latest version 5.2: 2015




What Kind of Language is Java?

COBOL and other 3GL* Words

• The Compiler creates an object from a source

*) 3GL: Third Generation Language, like PL/I and COBOL

COBOL and other 3GL Words

• A pseudo-assembler listing is produced on the way


• The Binder (Linker) binds the object into a program object or load module

.0..............................................................................0F00000000000000000000000000000000000000000000000000000000000000000000000000000030000000000000000000000000000000000000000000000000010000000000000000000000000000 ------------------------------------------------------------------------------ ...............................................................-........HELLOCOB000000000000000000000000000000000000000000000000000000000000000600000000CCDDDCDC30000001000000000000000000000000000000000000000000000000000000000000000885336362 ------------------------------------------------------------------------------ .........................................@[email protected]_CEESG0000000000000000000000000000000000000000008000000000000000000100008000000C6CCCECF310100020001000000000000000000000000000010000000000000000000030A0030000A3D355270 ------------------------------------------------------------------------------ ...03...........................................................................000FF00000000000000000000000000000000000000000000000000000000000000000000000000032003000000000000000000000000000000000000000000000000000000000000000000000000000 ------------------------------------------------------------------------------ ...........................ì[email protected]_CODE..000000000000000000000000000500000000000008000000000000000000100000000000C6CDCC00300100030001000000000000008800000000000010000000000000000000030A003000063D364500 ------------------------------------------------------------------------------ ........................................................................HELLOCOB000000000000000000000000000000000000000000000000000000000000100000000000CCDDDCDC31020004000300000000000000000000000000001000000000000000000000020300000A85336362


• The loader loads the program object into storage

• Allocates static storage• Fixes up relocatable addresses• Passes over control

IEWPLMH ...Ì......¢............Ì...........ð...........m...h................... CCEDDDC40007000000B00000000000070001000000080000000000090008000000010002000000049567348000083000000000080100000800040200000C00080300000400080400001C000405000010 ------------------------------------------------------------------------------ }00..CEE.......-}00.°Öå. .0.qÕ0................ð...q...*...q.......u...¦....ì0C.4FF10CCC000000064FF09ED041F29EF30F000000000000080009000500090002000A000700005FC1700413550028006070010C0C10048F047F0000000000007C0068000C00080004007400300000803C ------------------------------------------------------------------------------ æÈxÈ..j@æÈxd...Óx©..ìææ.ìææ.×õAàxd..×õæ.xd..çææ.vF..xó..xÈ..ìæ..ìææ.ìææ.ìæAàìææ.C7A70398C7A8021EAB025CC05CC0BCC4A801BCC0A8014CC2AC00AC00A7015C015CC05CC05CC45CC004740A1004740A2E740780008004FF14740FFF04740B800856007E01740380008000800480148004 ------------------------------------------------------------------------------ C_WSA ................................................................C6EEC4444444444400000000000000000000000000000000000000000000000000000000000000003D621000000000000000000000000000000000000000000000000000000000000000000000000000 ------------------------------------------------------------------------------ ...è..........çá<<!ä!â.ñâ(.ä!â!<...................ì.......ë.........ì.......ë..000500000000004444444404442444442232323000000000000500000005323200000523200005320024040000416185CCF3F2092D03F2FC005E1E10000B00000088000023D39849024048889083D398 ------------------------------------------------------------------------------ ...............LDLDM....@........@.....@.......@................................000000000000000DCDCD000080000000080000180010000800100000000000000000000000000000000000000000000343441000000000400000007000E0000000D00000000000000000000000000000

Java Source

• The Compiler compiles source into bytecode

• There is no linking/binding for Java– Each class is loaded separately on

demand

Java Bytecode

• Java bytecode is the instruction set of the Java virtual machine

• This is a symbolic representation

Compiled from "Hello.java"public class dk.xact.michael.BatchHello.Hello { public dk.xact.michael.BatchHello.Hello(); Code: 0: aload_0 1: invokespecial #8 // Method java/lang/Object."<init>":()V 4: return

public static void main(java.lang.String[]); Code: 0: getstatic #16 // Field java/lang/System.out:Ljava/io/PrintStream; 3: ldc #22 // String Hello from batch 5: invokevirtual #24 // Method java/io/PrintStream.println:(Ljava/lang/String;)V 8: return}

Java Bytecode

• Each bytecode is composed by one (or two) bytes that represent the instruction–Along with zero or more

bytes for passing parameters

ca fe ba be-00 00 00 33-00 22 07 00-02 01 00 20 .......3 ."......64 6b 2f 78-61 63 74 2f-6d 69 63 68-61 65 6c 2f dk/xact/ michael/42 61 74 63-68 48 65 6c-6c 6f 2f 48-65 6c 6c 6f BatchHel lo/Hello07 00 04 01-00 10 6a 61-76 61 2f 6c-61 6e 67 2f ......ja va/lang/4f 62 6a 65-63 74 01 00-06 3c 69 6e-69 74 3e 01 Object.. .<init>.00 03 28 29-56 01 00 04-43 6f 64 65-0d 0a 00 03 ..()V... Code....00 09 0c 00-05 00 06 01-00 0f 4c 69-6e 65 4e 75 ........ ..LineNu6d 62 65 72-54 61 62 6c-65 01 00 12-4c 6f 63 61 mberTabl e...Loca6c 56 61 72-69 61 62 6c-65 54 61 62-6c 65 01 00 lVariabl eTable..04 74 68 69-73 01 00 22-4c 64 6b 2f-78 61 63 74 .this.." Ldk/xact2f 6d 69 63-68 61 65 6c-2f 42 61 74-63 68 48 65 /michael /BatchHe6c 6c 6f 2f-48 65 6c 6c-6f 3b 01 00-04 6d 61 69 llo/Hell o;...mai6e 01 00 16-28 5b 4c 6a-61 76 61 2f-6c 61 6e 67 n...([Lj ava/lang2f 53 74 72-69 6e 67 3b-29 56 09 00-11 00 13 07 /String; )V......00 12 01 00-10 6a 61 76-61 2f 6c 61-6e 67 2f 53 .....jav a/lang/S79 73 74 65-6d 0c 00 14-00 15 01 00-03 6f 75 74 ystem... .....out01 00 15 4c-6a 61 76 61-2f 69 6f 2f-50 72 69 6e ...Ljava /io/Prin74 53 74 72-65 61 6d 3b-08 00 17 01-00 10 48 65 tStream; ......He6c 6c 6f 20-66 72 6f 6d-20 62 61 74-63 68 0d 0a llo.from .batch..00 19 00 1b-07 00 1a 01-00 13 6a 61-76 61 2f 69 ........ ..java/i6f 2f 50 72-69 6e 74 53-74 72 65 61-6d 0c 00 1c o/PrintS tream...

Java at Runtime

• The Java Classloader executes these steps for each class:– Load• Loading brings the bytecode into the JVM

– Link• Verification ensures the class/interface is structurally correct• Preparation involves allocating memory needed by the class/interface• Resolution resolves symbolic references

– Initialize• Initialization gives the proper initial values to the class variables




How is Java implemented on z?

The JVM is a Set of C++ Programs in zFS

Java Native Interface (JNI) is the Bridge

• JNI enables Java code running in a JVM to call and be called by native applications and libraries written in other languages

• Functionality implemented in separate C or C++ files– Convert native arrays to/from Java arrays, native strings to/from Java

strings, instantiate objects, throw exceptions, etc.

Sample COBOL JNI ProgramPROGRAM-ID. "DBBATCOB" RECURSIVE.REPOSITORY.

Class DbBatchJava is "DbBatchJava"Class jstring is "jstring".

WORKING-STORAGE SECTION.01 parmString OBJECT REFERENCE jstring.

LINKAGE SECTION.COPY JNI.

PROCEDURE DIVISION.Set address of JNIEnv to JNIEnvPtrSet address of JNINativeInterface to JNIEnvCALL "NewStringPlatform” USING BY VALUE JNIEnvPtr ADDRESS OF input-string ADDRESS OF parmString 0 RETURNING RC.INVOKE DbBatchJava "sayHello” USING BY VALUE parmString RETURNING RC.

Sample called Java Program

public class DbBatchJava {public static int sayHello(String inputString) {

System.out.println("DB Batch Java received " + inputString);return 4711;

}}

JDBC

• JDBC (Java Data Base Connection)• Lower part implemented as C++

program objects• Upper part implemented as Java

classes calling through JNI• Note that the jar files in the figure

are really symbolic links to the program objects in the /IBM folder

Which Runtimes?

• Batch – BPX – C:OZ– JZOS – BCD

• CICS– JVMServer

• JCICS • OSGi • JDBC Type 2 (Local)• SQLJ (Static)

– Liberty • PHP • Mobile • Servlets • JSP • SAML • JDBC Type 4 (Over TCP/IP)

• DB2 – Stored procedures

• IMS – JMP – JDBC

• MQ – WMQ API – jms

• WAS – ”Classic”– Liberty

• zLinux

All of them!




Challenges

Theory and Practice

• Processor been optimized for the JVM

• JVM has been optimized for the processor

• You should be at the highest level of both– Z13 boxes– Java 8

• In theory performance comparable between Java and 3GL

Theory and Practice

• In theory, there is no difference between theory and practice• But, in practice, there is

Theory and Practice

• Theory– You understand everything– Nothing works

• Practice– Everything works– Nobody knows why

• Here we unite theory and practice– Nothing works – Nobody understands why

Mainframe Issues

• Virtualization conflicts• JVM load and initalization CPU

usage• Garbage Collection Policies• Heap size tunings

Virtualization Conflicts

• Mainframe has excelled in virtual storage and virtual machines since the 1960’es– Based on a set of civilized traffic rules in a multi-tenant system

• Java has its own Virtual Machine– Raised as a spoiled only child with no manners– Grabs all the storage it can immediately

• Has been handled on z in different ways over time• JVM on top of Virtual Storage on top of z/OS perhaps on top of

z/VM on top of PR/SM...?

JVM Load and Initialization

• Can take a lot of MIPS– You should minimize loads– You should reuse JVM’s

Shared Class Cache

• A shared class area for one or more JVM’s improves startup time– Lots of classes are already preloaded

• Switch on shared classes with the -Xshareclasses command-line option– Virtual memory footprint reduction when using more than one JVM– Loading classes from a populated cache is faster than loading classes from disk– Improved startup– Classes are already in memory and partially verified– Benefits applications that regularly start new JVM instances doing similar tasks– Cost to populate an empty cache with a single JVM is minimal

• Both relevant for CICS and batch

CICS OSGi middleware bundles

• JVMProfile option OSGI_BUNDLES• Middleware bundles installed and activated in the OSGi

framework when JVM is initialized• OSGI_BUNDLES=/u/example/pathToBundleDirectory/B1.jar,\ /u/example/pathToBundleDirectory/B2.jar

Storage Differences

• Storage is static in COBOL, HLASM, PL/I etc.

• Storage is dynamic in Java• You should not call from Java to

COBOL with an area that has not yet been allocated by Java – Storage violations – Null pointer exceptions

COBOL Storage Allocation

• WORKING-STORAGE normally allocated from LE heap storage– If you declare it, it is being

allocated• LOCAL-STORAGE allocated

from LE stack storage• External variables allocated

from LE heap storage

• LE stack storage is automatically created by LE and is used for routine linkage and automatic storage

• LE heap storage is dynamically allocated at a routine's first request for storage that has a lifetime not related to the execution of the current routine

Java Storage Allocation from LE Heap

• The Java heap that garbage collection manages is allocated during JVM startup as a contiguous area of memory– Its size is that of the maximum Java heap size parameter– Allocate for the maximum heap size to ensure that one contiguous

area will be available should heap expansion occur• Explicit calls to malloc() by the JVM, or by any native JNI (Java

Native Interface) code that is running under that Java process– This includes application JNI code, and vendor-supplied native

libraries; for example, JDBC drivers

Garbage Collection

• Java normally does not do explicit allocation and deallocation

• Deallocation done as Garbage Collection (GC)– All active objects marked and copied

away– All unused deleted by compacting

storage– Done in different pools to handle

short and long lived objects separately

Garbage Collection Issues

• Pause time • Pause predictability • CPU usage • Memory footprint

– Virtual footprint – GC interaction with paging and

swapping • The unimaginable memory leaks

– Unintended object retention

IBM JVM Garbage Collection Policies

• -Xgcpolicy:optthruput– For “batch” type apps

• -Xgcpolicy:optavgpause – For apps with responsiveness criteria

• -Xgcpolicy:gencon – Highly transactional workloads

• -Xgcpolicy:subpools – Large systems with allocation

contention

Heap size tuning

• Java heap size tuning is an art– Small heaps get filled up quickly

• GC runs often– Large heaps hold a lot of objects

• Each GC takes a long time (”Stop the World”)– Need tools, measurements, statistics and tuning

• Java heaps lives on top of Language Environment heaps and z/OS virtual storage– LE heaps can be measured and tuned– Paging and swapping can be the result of overallocating heaps

Or you can just buy more Real Storage...

Health Center

• An agent is included in the IBM JVM in recent versions, so you don’t have to install anything

• A server is part of IBM Support Assistant Team Server– If you have the authority you can alternatively install it and run it on

your own workstation• A client can run in a browser or in Eclipse

IBM Support Assistant

Health Center Summary

Health Center CPU Usage

Health Center Garbage Collection

Health Center File I/O

Health Center Profiler

Health Center Thread Analysis




Development

Plain Java Development

• All Java tools can be used• Rational Developer for z has

support for special API’s like JCICS and for OSGi

• The IBM JVM is 100% compatible with Sun/Oracle from the development side– Differences only in JVM

implementation and in toolbox

Addressing Modes

• COBOL runs in 31 bit mode• Java can run in 31 or 64 bit

mode• Calling between 31 and 64 bit

programs can yield interesting results

Java in Batch• BPX– Unix batch launcher

• Co:Z– Executes the Unix program or shell in the same address space, which simplifies job

accounting and allows for the use of resources such as DD statements by the Unix program

• JZOS– Java batch launcher

• BCD– Managed environment for Java – Allows interoperability with COBOL and PL/I

BPXBATCH and BPXBATSL• USS batch launcher facilities

– Can launch a JVM in a batch job • BPXBATCH Limitations

– No flexible configuration of the USS environment for each job– No condition codes passed – Separate address space – No use of DD statements – Stderr and stdout not written before the step has finished

• BPXBATSL supports DD statements• C:OZ is an improved solution, supplied as Freeware from Dovetailed Technologies

JZOS• Java batch launcher

– Written in Java by Dovetailed Technologies and acquired by IBM• Call the JZOS batch launcher load module from JCL to create a JVM under UNIX

System Services• DD statements

– Java main class– Java version that is needed for this job– Classpath– Libpath– Additional JVM arguments, also from a PDSE member– JVM Encoding

JZOS Advantages

• Launcher and JVM run in the same address space • Makes job accounting easier • Allows the use of DD statements • System.out.println() and System.err.println() redirected to

SYSOUT and SYSERR• Easier to integrate in a scheduling environment

z/OS Batch Runtime (BCD)

• Java-focused, platform-neutral programming model• Managed environment for Java– Allows interoperability with COBOL and PL/I– Supports DB2 hybrid applications

• Initialization– Set up the job step under a Resource Recovery Services (RRS)

managed global transaction– Call the primary COBOL or Java application after initialization of the

environment

z/OS Batch Runtime (BCD)

• Mixed COBOL/PL/I and Java batch application with a shared DB2 connection– Coexistence of SQL, JDBC and SQLJ– Updates to DB2 are committed in the same unit of work

• Consistent with IBM WebSphere-based batch• Must run in 31 bit mode, because COBOL and PL/I are 31 bit• JZOS launches the Java program

com.ibm.zos.batch.container.BCDBatchContainer that invokes your Java, COBOL and PL/I programs

Seamless Debug in CICS

• COBOL & PL/I– Connect to DTCN in Host Connections– Create a DTCN Server Profile

• Java– Open RDz Debug Configurations – Start the Remote Java Application pointing to the Java project and

CICS• Run the transaction in CICS

Seamless debug: COBOL

Seamless debug: Java

Seamless debug: COBOL again




Security

Batch and CICS Liberty

• EJBROLE– Member class for Enterprise Java Beans

authorization roles• GEJBROLE

– Grouping class for Enterprise Java Beans authorization roles

• JAVA– Contains profiles that are used by Java

for z/OS applications to perform authorization checking for Java for z/OS resources

EJBROLE Examples

• ADMINISTRATOR • ADMINSECURITYMANAGER • BBNBASE.deployer • BBNBASE.CosNamingCreate

• COSNAMINGCREATE • OPERATOR • IZUDFLT.*.izuUsers (G)

• isCallerInRole()• isUserInRole()

CICS JVMServer

• Normal CICS RACF security– Transactions– Programs– Etc.

• Java OSGi Security Manager– Forbid System.exit()




Education

What do I need to learn?

• Object Orientation– Inheritance– Encapsulation– Polymorphism

• Java syntax & semantics• Libraries

– Supplied with Java– Supplied by IBM– Open source

• Development tools– Eclipse– RDz– Mapping tools– ...

• Performance tools• Site & business specific

knowledge




Moderniza-tion

Conversion

BusinessSoftware

Consultants




Thank you for your attention

Java is a new language on the mainframe

Software

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