JDK 9: Mission Accomplished. What Next For Java?

© Copyright Azul Systems 2017
@speakjava
JDK 9: Mission Accomplished
What Next For Java?
Simon Ritter
Deputy CTO, Azul Systems
1

JDK 9

JDK 9: Big And Small Changes
3

Java Platform Module System
 The core Java libraries are now a set of modules
– 97 modules for JDK, 28 of which are Java SE
– No more rt.jar or tools.jar files
 Most internal APIs are now encapsulated
– sun.misc.Unsafe, etc.
– Numerous libraries and frameworks use internal APIs
 Module path used to locate modules
– Separate and distinct from classpath
4

JDK 9 And Compatibility
5
"Clean applications that just depend on java.se
should just work" - Oracle
The java.se.ee module is not included on the
modulepath for javac or the JVM by default

JPMS And Existing Applications
 Initially, leave everything on the classpath
 Anything on the classpath is in the unnamed module
– All packages are exported
– The unnamed module depends on all modules
 Migrate to modules as required
– Try automatic modules
– Move existing jar files from classpath to modulepath
6

Breaking Encapsulation
 "The Big Kill Switch" to turn off encapsulation
– --illegal-access
 permit: Warning for first use of an encapsulated API
 warn: Warning for every use of an encapsulated API
 debug: Warning and stack trace for every use
 deny: No access to encapsulated APIs
7

Breaking Encapsulation
 Allowing direct access to encapsulated APIs
– --add-exports
 Allowing reflective access to encapsulated APIs
– --add-opens
8
--add-exports java.management/com.sun.jmx.remote.internal=mytest
--add-exports java.management/sun.management=ALL-UNNAMED
--add-opens java.base/java.util=ALL-UNNAMED

jlink: The Java Linker (JEP 282)
9
Modular run-time
image
…confbin
jlink
$ jlink --modulepath $JDKMODS
--addmods java.base –output myimage
$ myimage/bin/java –-list-modules
java.base@9
jmods

jlink: The Java Linker (JEP 282)
$ jlink --module-path $JDKMODS:$MYMODS
--addmods com.azul.app –-output myimage
$ myimage/bin/java –-list-modules
java.base@9
java.logging@9
java.sql@9
java.xml@9
com.azul.app@1.0
com.azul.zoop@1.0
com.azul.zeta@1.0

The Implications Of jlink
 "Write once, run anywhere"
– Long term Java slogan, mainly held true
 jlink generated runtime may not include all Java SE
modules
– But is still a conformant Java implementation
– To be conformant:
 It must include the java.base module
 If other modules are included, all transitive module dependencies
must also be included
– Defined as a closed implementation

JDK Development Changes

OpenJDK: New Release Model
 A new version of the JDK will be released every six months
– March and September
– Starting next year
 OpenJDK development will be more agile
– Previous target was a release every two years
 Three and a half years between JDK 8 and JDK 9
 Features will be included only when ready
– Targeted for a release when feature complete
– Not targeted at specific release when started
13

OpenJDK: More Open Source
 Oracle will open-source closed-source parts of the JDK
– Flight recorder
– Mission control
 The goal is for there to be no functional difference between
an Oracle binary and a binary built from OpenJDK source
– Targeted for completion late 2018
14

JDK Version Numbering
 New scheme introduced in JDK 9 (JEP 223)
– JDK ${MAJOR}.${MINOR}.${SECURITY}
– Semantic versioning
– Easier to understand by humans and computers
15

 New proposal for subsequent releases
– JDK ${YEAR}.${MONTH}
 JDK 18.3, JDK 18.9, etc.
– Same concept as used by Ubuntu
– Many people not happy about this
16

 New, new scheme. Just proposed
– $FEATURE.$INTERIM.$UPDATE.$EMERG
– FEATURE: Was MAJOR, i.e. 10, 11, etc.
– INTERIM: Was MINOR. Reserved for future use
– UPDATE: Was SECURITY, but with different incrementing rule
– EMERG: Emergency update outside planned schedule
17

Availability Of JDK Updates
 Oracle are switching to a long term support (LTS) model
 LTS release will have 3 years of public updates
– JDK 8 has been classified as an LTS release
 It will have updates for more than 3 years
– Next LTS release will be September, 2018
 Non-LTS releases are "Feature Releases"
– JDK 9 is a feature release
– Public updates only until next feature release
 JDK 9 public updates end in March, 2018
18

Deprecated in JDK 9: Soon To Go
 Applets as a deployment mechanism
 CMS garbage collector
 Java policy tool, jconsole, Doclet API, other small things
 java.se.ee meta-module
 java.corba
 java.transaction
 java.activation
 java.xml.bind
 java.xml.ws
 java.xml.ws.annotation
19

Oracle Binaries
 Until now released under Oracle Binary Code License
– Have to accept to download
– Classic "field-of-use" restriction
 Moving forward
– Binaries available under GPLv2 with CPE
– No more 32-bit binaries
– No more ARM binaries
– Windows, Linux, Mac and Solaris SPARC only
 All 64-bit
20

JDK.${NEXT}

JDK 18.3 10
 JSR 383 submitted and expert group formed
– Lead by Brian Goetz
– Oracle, IBM, Red Hat, SAP and Azul (Me)
 Schedule approved
– Development complete: 14/12/17
– Release candidate: 22/2/18
– General Availability: 20/3/18
 Early draft review already published
22

JDK 18.3 10 (Current)
 JEP 286: Local variable type inference
var list = new ArrayList<String>(); // infers ArrayList<String>
var stream = list.stream(); // infers Stream<String>
 A few small API changes
– New replace method in java.util.Properties
– New toString method in java.util.concurrent.FutureTask
– Two new methods in java.lang.StackWalker.StackFrame
– Four new methods in java.util.concurrent.locks.StampedLock
23

Longer Term JDK Futures

Interesting Future JEPs
 JEP 304: GC Interface
– Internal JVM interface to allow easy change of GC
– Nice for us at Azul
 JEP 305: Pattern matching
– Type test and switch statement support to start
 JEP 310: Application class data sharing (CDS)
– Extend CDS to include application classes as well as JDK
 JEP 312: Thread-local handshakes
– JVM ability to stop individual threads
– Lower latency
25

Project Amber
 JEP 286: Local variable type inference
– Already included in JDK 10
 JEP 301: Enhanced enums
– Generic enums
– Sharper type-checking of constants
 JEP 302: Lambda leftovers
– Underscores for unused parameters
– Shadowing of Lambda parameters
– Better disambiguation of functional expressions
26

Project Valhalla
 Value types in Java
 Why do we need them?
27
Identity leads to pointers
Pointers lead to indirection
Indirection leads to suffering
(of performance)

Project Valhalla
 Java has:
– Primitives: for performance
– Objects: for encapsulation, polymorphism, inheritance, OO
 Problem is where we want to use primitives but can't
– ArrayList<int> won't work
– ArrayList<Integer> requires boxing and unboxing,
object creation, heap overhead, indirection reference
28

Project Valhalla
 Value types
 "Codes like a class, works like a primitive"
– Can have methods and fields
– Can implement interfaces
– Can use encapsulation
– Can be generic
29

Project Panama
 Interconnecting JVM and native code
– Native function calls from JVM (C, C++)
– Native data access from JVM or inside JVM heap
– Header file API extraction tools
– Native library management APIs
– Class and method resolution “hooks”
– Native-oriented JIT optimizations
30

Project Loom
 Further work on making concurrent programming simpler
 Threads are too heavyweight
– Too much interaction with operating system
 Loom will introduce fibres
– JVM level threads (remember green threads?)
– Add continuations to the JVM
– Use the ForkJoinPool scheduler
– Much lighter weight than threads
 Less memory
 Close to zero overhead for task switching
31

Conclusions

Java Continues Moving Forward
 JDK 9 is out
– But not an LTS
– JPMS may require changes to existing applications
 Faster Java releases
– Feature release every 6 months, LTS every 3 years
– OpenJDK binaries under GPLv2 with CPE license
 Lots of ideas to improve Java
– Value types, better JNI, better type inference
– Many smaller things
33

Zulu Java
 Azul’s binary distribution of OpenJDK
– Passes all TCK tests
– Multi-platform (Windows, Linux, Mac)
– FREE!
 Happy to sell you support, including older versions
 JDK 6, 7, 8 and 9
34
www.zulu.org/download

@speakjava
Thank you!
Simon Ritter
Deputy CTO, Azul Systems
35

JDK 9: Mission Accomplished. What Next For Java?

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