JDK 9 and JDK 10 Deep Dive

© Copyright Azul Systems 2016
@speakjava
JDK 9 and 10 Deep Dive
Simon Ritter
Deputy CTO, Azul Systems
1

JDK 9: 86 Changes
2

JDK 9: Agenda
 Java Platform Module System
 Developer features
 Other things
 Migrating applications to JDK 9
– Real world example
3

© Copyright Azul Systems 2016 4
JPMS: API Structural Changes

API Classification
 Supported, intended for public use
– JCP specified: java.*, javax.*
– JDK specific: some com.sun.*, some jdk.*
 Unsupported, not intended for public use
– Mostly sun.*
– Most infamous is sun.misc.Unsafe
5

General Java Compatability Policy
 If an application uses only supported APIs on version N of
Java it should work on version N+1, even without
recompilation
 Supported APIs can be removed
–But only with advanced notice
 JDK 8 has 18 interfaces, 23 classes, 64 fields, 358
methods and 20 constructors that have been deprecated
–None have been removed
–Until now
6

Most Popular Unsupported APIs
1. sun.misc.BASE64Encoder
2. sun.misc.Unsafe
3. sun.misc.BASE64Decoder
7
Oracle dataset based on internal application code

JDK Internal API Classification
 Non-critical
– Little or no use outside the JDK
– Used only for convenience (alternatives exist)
 Critical
– Functionality that would be difficult, if not impossible to
implement outside the JDK
8

JEP 260 Proposal
 Encapsulate all non-critical JDK-internal APIs
 Encapsulate all critical JDK-internal APIs, for which
supported replacements exist in JDK 8
 Do not encapsulate other critical JDK-internal APIs
– Deprecate these in JDK 9
– Plan to encapsulate or remove them in the future
– Command-line option to access encapsulated critical APIs
 --add-exports
 --add-opens
9

JEP 260 Accessible Critical APIs
 sun.misc.Unsafe
 sun.misc.Signal
 sun.misc.SignalHandler
 sun.misc.Cleaner
 sun.reflect.Reflection.getCallerClass
 sun.reflect.ReflectionFactory
10

Project Jigsaw And Modules

Goals For Project Jigsaw
 Make Java SE more scalable and flexible
– Internet of Things
– Microservices
 Improve security, maintainability and performance
 Simplify construction, deployment and maintenance of
large scale applications
 Eliminate classpath hell
12

Module Fundamentals
 Module is a grouping of code
– For Java this is a collection of packages
 Modules can contain other things
– Native code
– Resources
– Configuration data
13
com.azul.zoop
com.azul.zoop.alpha.Name
com.azul.zoop.alpha.Position
com.azul.zoop.beta.Animal
com.azul.zoop.beta.Reptile
com.azul.zoop.theta.Zoo
com.azul.zoop.theta.Lake

Module Declaration
14
module com.azul.zoop {
}
module-info.java
com/azul/zoop/alpha/Name.java
com/azul/zoop/alpha/Position.java
com/azul/zoop/beta/Animal.java
com/azul/zoop/beta/Reptile.java
com/azul/zoop/theta/Zoo.java
com/azul/zoop/theta/Lake.java

Module Dependencies
requires com.azul.zeta;
} com.azul.zoop
com.azul.zeta

Module Dependencies
module com.azul.zapp {
requires com.azul.zoop;
requires java.sql;
}
com.azul.zapp
com.azul.zoop java.sql

Module Dependency Graph
com.azul.zapp
java.base
java.sqlcom.azul.zoop
com.azul.zeta
java.xml java.logging
explicit
implicit

Module Dependency Graph
 No missing dependencies
 No cyclic dependencies
 No split packages
18

Readability v. Dependency
com.azul.zapp
java.sql
java.logging
module java.sql {
requires transitive java.logging;
}
Driver d = …
Logger l = d.getParentLogger();
l.log(“azul’);
Implied readability

Module Implied Readability Graph
com.azul.zapp
java.base
java.sqlcom.azul.zoop
com.azul.zeta
java.xml java.logging
explicit
implicit
implied

Package Visibility
exports com.azul.zoop.alpha;
exports com.azul.zoop.beta to com.azul.zapp;
}
com.azul.zoop
com.azul.zoop.alpha
com.azul.zoop.beta
com.azul.zoop.thetacom.azul.zapp only

More Package Visibility
open module com.azul.zoop {
}
com.azul.zoop
com.azul.zoop.alpha
com.azul.zoop.beta
com.azul.zoop.theta
com.azul.zoop.alpha
com.azul.zoop.beta
com.azul.zoop.theta
REFLECTIONIMPORT

Even More Package Visibility
exports com.azul.zoop.alpha;
exports com.azul.zoop.beta to com.azul.zapp;
opens com.azul.theta;
}
com.azul.zoop
com.azul.zoop.theta
REFLECTIONIMPORT
com.azul.zoop.alpha
com.azul.zoop.beta
com.azul.zapp only

Restricted Keywords
module
requires requires;
exports exports to to;
module {
opens opens;
}

Optional Dependencies
 Required at compile time
 Possibly not needed at runtime
– If it is generates a NoClassDefFoundError
 Use static keyword
– Oddly this used to be optional, which is more logical
25
module mine.lib {
requires static com.google.guava
}

Accessibility
 For a package to be visible
– The package must be exported by the containing module
– The containing module must be read by the using module
 Public types from those packages can then be used
com.azul.zoopcom.azul.zapp
reads

Java Accessibility (pre-JDK 9)
public
protected
<package>
private

Java Accessibility (JDK 9)
public to everyone
public, but only to specific modules
public only within a module
protected
<package>
private
public ≠ accessible (fundamental change to Java)

JDK 8 Dependencies

The java.base Module
module java.base {
exports java.lang;
exports java.io;
exports java.net;
exports java.util;
}

JDK 9 Platform Modules
31
java.se
java.compact3
java.compact2
java.compact1
java.scripting
java.instrument
java.base
java.logging
java.sql
java.sql.rowset
java.xml
java.desktop
java.rmi
java.prefs
java.datatransfer
java.compiler
java.management
java.security.jgss
java.naming
java.security.sasl
All modules depend on java.base
no implied
readability=

JDK 9 Platform Modules
32
java.se.e
e
java.se
java.xml.bind
java.corba
java.compiler
java.desktop
java.annotations.common
java.rmi
java.datatransfer
java.management
java.xml.ws
java.naming
java.transaction
java.activation
All modules depend on java.base

Using Modules

Module Path
$ javac –modulepath dir1:dir2:dir3

Compilation With Module Path
35
$ javac –-module-path mods –d mods
src/module-info.java
src/com/azul/zoop/alpha/Name.java
mods/module-info.class
mods/com/azul/zoop/alpha/Name.class
src/module-info.java
src/com/azul/zoop/alpha/Name.java

Application Execution
 --module-path can be abbreviated to -p
$ java –p mods –m com.azul.zapp/com.azul.zapp.Main
Azul application initialised!
module name main class

Packaging With Modular JAR Files
mods/module-info.class
mods/com/azul/zapp/Main.class
$ jar --create --file=mylib/zapp.jar
--main-class=com.azul.zapp.Main
-C mods .
module-info.class
com/azul/zapp/Main.class
zapp.jar

JAR Files & Module Information
$ jar --file=mylib/zapp.jar –-print-module-descriptor
$ jar --file=mylib/zapp.jar -d
com.azul.zapp
requires com.azul.zoop
requires com.azul.zeta
requires mandated java.base
requires java.sql
main-class com.azul.zapp.Main

Application Execution (JAR)
$ java –p mylib:mods –m com.azul.zapp
Azul application initialised!

Linking
Modular run-time
image
…confbin
jlink
$ jlink --module-path $JDKMODS
--add-modules java.base –-output myimage
$ myimage/bin/java –-list-modules
java.base@9.0

Linking An Application
$ jlink --module-path $JDKMODS:$MYMODS
--add-modules com.azul.zapp –-output myimage
$ myimage/bin/java –-list-modules
java.base@9
java.logging@9
java.sql@9
java.xml@9
com.azul.zapp@1.0
com.azul.zoop@1.0
com.azul.zeta@1.0
Version numbering for
information purposes only
“It is not a goal of the module
system to solve the version-
selection problem”

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 conforming Java implementation
– To conform to the specification, the runtime:
 Must include the java.base module
 If other modules are included, all transitive module dependencies
must also be included
– Defined as a closed implementation

Application Migration

Typical Application (JDK 8)
jar
jar
jar
JDK
jar
jarjar
jar jar
jar
jar
jar
jar
Classpath

Typical Application (JDK 9)
jar
jar
jar
module
java.base
module
java.desktop
module
java.datatransfer
module
java.xml
jar
jarjar
jar jar
jar
jar
jar
jar
Unnamed
module

Sample Application
myapp.ja
r
libgl.jar
mylib.jar
gluegen.jar jogl.jar
module
java.base
module
java.desktop
module
java.datatransfer
module
java.xml

Run Application With Classpath
$ java –classpath
lib/myapp.jar:
lib/mylib.jar:
lib/libgl.jar:
lib/gluegen.jar:
lib/jogl.jar:
myapp.Main

Sample Application
module
myapp.ja
r
libgl.jar
module
mylib.jar
gluegen.jar jogl.jar
module
java.base
module
java.desktop
module
java.datatransfer
module
java.xml

Application module-info.java
module myapp {
requires mylib;
requires java.base;
requires java.sql;
requires libgl; ????
requires gluegen; ????
requires jogl; ????
}

Sample Application
module
myapp.ja
r
module
libgl.jar
module
mylib.jar
module
gluegen.jar
module
jogl.jar
module
java.base
module
java.desktop
module
java.datatransfer
module
java.xml

Automatic Modules
 Real modules
 Simply place unmodified jar file on module path
– Rather than classpath
 No changes to JAR file
 Module name derived from JAR file name
 Exports all its packages
– No selectivity
 Automatically requires all modules on the module path
51

Application Module Dependencies
module
myapp.ja
r
module
libgl.jar
module
mylib.jar
module
gluegen.jar
module
jogl.jar
module
java.base
module
java.desktop
module
java.datatransfer
module
java.xml
Implicit
Explicit

Run Application With Modules
$ java –classpath
lib/myapp.jar:
lib/mylib.jar:
lib/libgl.jar:
lib/gluegen.jar:
lib/jogl.jar:
myapp.Main
$ java –p mylib:lib –m myapp

Advanced Details

Modular Jar Files And JMODs
 Modular jar files are simple
– Standard jar file possibly with module-info.class file
– Can use existing (unmodified) jar files
 JMOD files
– More complex module files
– Used for modules in the JDK
– Can include native files (JNI), configuration files and
other data
– Based on zip file format (pending final details - JEP 261)
55

jmod Command
 Create can specify several details:
– Main class
– Native libraries and commands
– Configuration data
– OS name, version and machine architecture
 Details included in module-info.class file
56
jmod (create | list | describe) <options> <jmod-file>

Classloaders (Since JDK 1.2)
57
Bootstrap classloader (Internal Class)
Bootstrap Class Path
Extension classloader (URLClassLoader)
Extension Mechanism
Application classloader (URLClassLoader)
Class Path

Classloaders (JDK 9)
58
Bootstrap classloader (Internal Class)
bootstrap class path
Platform classloader (Internal Class)
JDK classes with specific permissions
Application classloader (Internal Class)
Class & Module Path

Services
module java.sql {
requires transient
java.logging;
requires transient java.xml;
exports java.sql;
exports javax.sql;
exports javax.transaction.xa;
uses java.sql.Driver;
}

Services
module com.mysql.jdbc {
requires java.sql;
exports com.mysql.jdbc;
provides java.sql.Driver with com.mysql.jdbc.Driver;
}

Avoiding Cyclic Dependencies
logging.api logging.impl
http.client

Avoiding Cyclic Dependencies
logging.api logging.impl
http.client
interface Logger
class HttpLogger
implements Logger
uses Logger
provides Logger
with HttpLogger

Incubator Modules (JEP 11)
 Develop APIs without making them part of the standard
– At least not straight away
 Allow developers to “kick the tyres”
– Not always possible to get a new API right first time
 Move from incubator to full module
– Becomes part of the standard
 JDK 9 only has one incubator: HTTP/2 (JEP 110)
 Some concerns about fragmentation
--do-not-resolve-by-default
64

JDK 9 Developer Features

Java Language

Milling Project Coin (JEP 213)
 Single underscore is now a reserved word
– No longer usable as an identifier
– Two or more underscores still works
 Allow @SafeVarargs on private instance methods
– In addition to constructors, final and static methods
67

Milling Project Coin
 Private methods are now permitted in interfaces
– Separate common code for default and static methods
68
public interface MyInterface {
default int getX() {
return getNum() * 2;
};
static int getY() {
return getNum() * 4;
}
private static int getNum() {
return 12;
}
}

 Effectively final variables in try-with-resources
69
BufferedReader reader =
new BufferedReader(new FileReader("/tmp/foo.txt"));
try (BufferedReader myReader = reader) {
myReader.lines()
.forEach(System.out::println);
}
JDK 8
try (reader) {
reader.lines()
}
JDK 9

 Diamond operator with anonymous classes
– Type inference can infer a non-denotable type
– If the type inferred can be denotable you can use <>
70
public abstract class Processor<T> {
abstract void use(T value);
}
Processor<String> processor = new Processor<>() {
@Override
void use(String value) {
// Some stuff
}
};

Core Libraries

Factory Methods For Collections (JEP 269)
 The problem:
– Creating a small unmodifiable collection is verbose
72
Set<String> set = new HashSet<>();
set.add("a");
set.add("b");
set.add("c");
set = Collections.unmodifiableSet(set);

Factory Methods For Collections (JEP 269)
 Static methods added to List, Set and Map interfaces
– Create compact, immutable instances
– 0 to 10 element overloaded versions
– Varargs version for arbitary number of elements
73
Set<String> set = Set.of("a", "b", "c");
List<String> list = List.of("a", "b", "c");
Map<String, String> map = Map.of(“k1”, “v1”, “k2”, “v2”);
Map<String, String> map = Map.ofEntries(
entry(“k1”, “v1”), entry(“k2”, “v2”));

Stream Enhancements
 Collectors.flatMapping()
– Returns a Collector that converts a stream from one
type to another by applying a flat mapping function
74
Map<String, Set<LineItem>> items = orders.stream()
.collect(groupingBy(Order::getCustomerName,
flatMapping(order -> order.getLineItems().stream(), toSet())));

Improved Iteration
 iterate(seed, hasNext, next)
– Can be used like the classic for loop
75
Initial
value
Predicate UnaryOperator
IntStream.iterate(0, i -> i < 10, i -> ++i)
IntStream.iterate(0, i -> i < 10, i -> i++)
Infinite stream

Stream takeWhile
 Stream<T> takeWhile(Predicate<? super T> p)
 Select elements from stream while Predicate matches
 Unordered stream needs consideration
thermalReader.lines()
.mapToInt(i -> Integer.parseInt(i))
.takeWhile(i -> i < 56)

Stream dropWhile
 Stream<T> dropWhile(Predicate<? super T> p)
 Ignore elements from stream while Predicate matches
 Unordered stream still needs consideration
thermalReader.lines()
.mapToInt(i -> Integer.parseInt(i))
.dropWhile(i -> i < 56)

dropWhile/takeWhile
 Be careful of unordered streams missing values
78
list.stream()
.dropWhile(s -> s.charAt(0) < ‘e')
List<String> list = List.of("alpha", "bravo", "charlie",
"delta", "echo", "foxtrot");
list.stream()
.takeWhile(s -> s.length() == 5)
alpha
bravo
echo
foxtrot

Additional Stream Sources
 Matcher stream support
– Stream<MatchResult> results()
 Scanner stream support
– Stream<MatchResult> findAll(String pattern)
– Stream<MatchResult> findAll(Pattern pattern)
– Stream<String> tokens()
79

Additional Stream Sources
 java.net.NetworkInterface
– Stream<InetAddress> inetAddresses()
– Stream<NetworkInterface> subInterfaces()
– Stream<NetworkInterface> networkInterfaces()
 static
 java.security.PermissionCollection
– Stream<Permission> elementsAsStream()
80

Parallel Support For Files.lines()
 Memory map file for UTF-8, ISO 8859-1, US-ASCII
– Character sets where line feeds easily identifiable
 Efficient splitting of mapped memory region
 Divides approximately in half
– To nearest line feed
81

Parallel Lines Performance
82

Optional: New Methods
 ifPresentOrElse(Consumer action, Runnable emptyAction)
– If a value is present call accept() on action with the value
– Otherwise, run the emptyAction
 Not in a separate thread
 or(Supplier<? extends Optional<? extends T>> supplier)
– Return the Optional if there is a value
– Otherwise, return a new Optional created by the Supplier
 stream()
– Returns a stream of zero or one element
83

Smaller Features
 Process API updates (JEP 102)
– Native process
– Process/ProcessHandle/ProcessHandle.Info
 Process.toHandle()
– More information about process
 Command. command line, arguments, CPU duration, user
– Control subject to security manager permissions
84

Multi-Release Jar Files (JEP 238)
 Multiple Java release-specific class files in a single archive
 Enhance jar tool to create multi-release files
 Support multi-release jar files in the JRE
– Classloaders
– JarFile API
 Enhance other tools
– javac, javap, jdeps, etc.
 Also, modular jar files
85

© Copyright Azul Systems 2016 86
jshell
Read-Eval-Print Loop
(REPL)
Demo

Spin-Wait Hints (JEP 285)
 Proposed by Azul
– We rock!
 A new method for Thread class
– onSpinWait()
 Enables the x86 PAUSE instruction to be used from Java
code
– If available
– Ignored otherwise
– Improved performance for things like Disruptor
87

Reactive Streams (JEP 266)
 Reactive streams publish-subscribe framework
 Asynchronous, non-blocking
 Flow
– Publisher, Subscriber, Processor, Subscription
 SubmissionPublisher utility class
– Asynchronously issues items to current subscribers
– Implements Flow.Processor
88

Reactive Streams: The Problem
89
Publisher Subscriber
Process
Process
Process
Process
BLOCK

Reactive Streams: Flow API
 Set of interfaces
 Publisher
– Producer of items to be received by Subscribers
 Subscriber
– Receiver of messages
 Processor
– Both a Publisher and Subscriber (chaining)
 Subscription
– Message control linking a Publisher and Subscriber
90

Reactive Streams: Flow API
 Publisher
– subscribe(Subscriber)
 Subscriber
– OnSubscribe(Subscription)
– onNext(T item)
– onComplete() / onError(Throwable)
 Subscription
– request(long)
– cancel()
91

Solution
92
Publisher Subscriber
Subscription
request(4)
subscribe
onSubscribe
onItem
onItem
onItem
onItem
request(2)

Concurrency Updates (JEP 266)
 CompletableFuture additions
– Delays and timeouts
– Better support for sub-classing
– New static utility methods
 minimalCompletionStage
 failedStage
 newIncompleteFuture
 failedFuture
93

Variable Handles (JEP 193)
 Replacement for parts of sun.misc.Unsafe
 Fence operations
– Fine grained memory control
– Atomic operations on object fields and array elements
 VarHandle
– compareAndExchange(), compareAndSet()
– getAndAdd(), getAndSet()
– acquireFence(), releaseFence()
94

JDK 9 Other Features

Enhanced Deprecation (JEP 277)
 We have @deprecated and @Deprecated
– Used to cover too many situations
 New methods in Deprecated annotation
– boolean forRemoval()
 Will this ever be removed?
– String since()
 JDK Version when this was deprecated
 Several @Deprecated tags added
– java.awt.Component.{show(),hide()} removed
 jdeprscan command to produce report
96

Default Collector: G1 (JEP 248)
 G1 now mature in development
 Designed as low-pause collector
 Concurrent class unloading (JEP 156) JDK8u40
– Useful enhancement to improve G1
 Still falls back to full compacting collection
– Pause times proportional to heap size
– Use Zing from Azul for truly pauseless
97

Better String Performance
 Compact strings (JEP 254)
– Improve the space efficiency of the String class
– Not using alternative encodings
 Store interned strings in CDS archive (JEP 250)
– Share String and char[] objects between JVMs
 Indify String concatenation (JEP 280)
– Change from static String-concatenation bytecode
sequence to invokedynamic
– Allow future performance improvements
98

JIT Compiler Control (JEP 165)
 Control of C1/C2 JIT
– Directive file
– Runtime changes via jcmd
99

Compiler Directive Example
[ //Array of directives
{ //Directive Block
//Directive 1
match: ["java*.*","oracle*.*"],
c1: { Enable: true, Exclude: true, BreakAtExecute: true, },
c2: { Enable: false, MaxNodeLimit: 1000, },
BreakAtCompile: true, DumpReplay: true,
}, { //Directive Block
//Directive 2
match: ["*Concurrent.*"],
c2: { Exclude:true, },
},
]

AOT Compilation (JEP 295)
 Experimental feature in JDK 9
– -XX:+UnlockExperimentalVMOptions
– Only the java.base module has an AOT version
 jaotc command
– jaotc --output libMyStuff.so MyStuff.jar
 JVM uses AOT code to replace interpreted
– Can recompile with C1 to collect further profiling data
– Recompile with C2 for optimum performance
101

AOT Compilation
 Future use
 Project Metropolis
– Rewrite the JVM in Java
– Start with AOT code, profile and recompile with JIT
102

Migrating Applications To JDK 9

Migration Guidance From Oracle
104
"Clean applications that just depend on java.se
should just work"

Java Platform Module System
 We now have both classpath and modulepath
 No more rt.jar or tools.jar
 Dealing with internal API encapsulation
105

Migrating Applications to JPMS
 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
106

Reversing Encapsulation
 "The Big Kill Switch"
--illegal-access
 Four options:
– permit (current default)
– warn
– debug
– deny (future default)

 Big kill switch overrides encapsulation
– From the unnamed module (i.e. classpath)
– Allows unlimited refective access to named modules
 Not from named modules
 Warning messages written to error stream
 Useful to understand use of --add-exports and -
-add-opens when migrating to named modules

 Allowing direct access to encapsulated APIs
– --add-exports
 Allowing reflective access to encapsulated APIs
– --add-opens
109
--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

 Using the JAR file manifest
110
Add-Exports: java.base/sun.security.provider

Finding Encapsulated API Use
 jdeps
– Analyses dependencies on APIs
 Example: Minecraft
111
jdeps --list-deps 1.8.jar
java.base
java.datatransfer
java.desktop
java.management
java.naming
not found
unnamed module: 1.8.jar

"Missing" Modules
 Remember, "Clean applications that only use java.se..."
 The java.se.ee module not included by default
– Compilation and runtime
 Affected modules
– java.corba
– java.transaction
– java.activation
– java.xml.bind
– java.xml.ws
– java.xml.ws.annotation
112

Using "Missing" Modules
 Use the command line option
– --add-modules java.corba
 All modules (except CORBA) have standalone versions
– Maven central
– Relevant JSR RI
 Deploy standalone version on the upgrade module path
– --upgrade-module-path <path>
 Deploy standalone version on the classpath
113

Small Incompatibilities

 A single underscore is now a keyword in Java
 Fear not, two or more underscores can still be used
115
error: as of release 9, '_' is a keyword, and may not be used as
an identifier

Deleted Deprecated Methods
 Classes
– java.util.jar.Pack200
– java.util.jar.Unpack200
– java.util.logging.LogManager
 Methods
– addPropertyChangeListener()
– removePropertyChangeListener()
 Removal required for clean modularisation
116

Deleted Deprecated Class
 com.sun.security.auth.callback.DialogCallbackHandler
 Part of the Java Authentication and Authorisation Service
– JAAS
– Deprecated in JDK 7
117

Finding Deprecated API Use
 jdeprscan
– New tool in JDK 9
– Statically analyses class files and jar files against Java
SE APIs
– Looks for and reports usage of deprecated Java SE APIs
118

JDK/JRE File Structure (JEP 220)
119
bin
Pre-JDK 9 JDK 9
lib
tools.jar
jre
bin
rt.jar
lib
libconfbin
jre directory
tools.jar
rt.jar
jmods

JDK Version String Format
 Old
– Limited update release/Critical patch update (CPU)
– Download: Java SE 8u131
 java -version: jdk1.8.0_131
– Which has more patches, JDK 7u55 or JDK 7u60?
120

JDK Version Numbering
 New, new scheme. JEP 322
– $FEATURE.$INTERIM.$UPDATE.$PATCH
– FEATURE: Was MAJOR, i.e. 10, 11, etc.
– INTERIM: Was MINOR. Always zero, reserved for future use
– UPDATE: Was SECURITY, but with different incrementing rule
– PATCH: Emergency update outside planned schedule
121

Non-Programmatic Issues
 Java Network Launch Protocol (JNLP) [JSR 52]
– Now uses strict parsing of configuration files
– Some files that did parse may now fail
 Extension mechanism/Endorsed Standards Override
mechanisms removed
– Directories removed
 $JAVA_HOME/lib/ext
 $JAVA_HOME/lib/endorsed
122
<JAVA_HOME>/lib/ext exists, extensions mechanism no longer
supported; Use -classpath instead.
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

Removed GC Options (JEP 214)
 Deprecated in JDK 8 (JEP 173)
123
DefNew + CMS : -XX:-UseParNewGC -XX:+UseConcMarkSweepGC
ParNew + SerialOld : -XX:+UseParNewGC
ParNew + iCMS : -Xincgc
ParNew + iCMS : -XX:+CMSIncrementalMode -XX:+UseConcMarkSweepGC
DefNew + iCMS : -XX:+CMSIncrementalMode -XX:+UseConcMarkSweepGC
-XX:-UseParNewGC
CMS foreground : -XX:+UseCMSCompactAtFullCollection
CMS foreground : -XX:+CMSFullGCsBeforeCompaction
CMS foreground : -XX:+UseCMSCollectionPassing

JVM Logging
 Unified JVM logging (JEP 158)
– Common logging system for all components of JVM
 Unified GC logging (JEP 271)
– Re-implement GC logging using unified JVM logging
– Many command line options changed
124

Removed JVM Flags: Ignored
125
 AdaptiveSizePausePolicy
 CodeCacheMinimumFreeSpace
 DefaultThreadPriority
 JNIDetachReleasesMonitors
 LazyBootClassLoader
 NmethodSweepCheckInterval
 NmethodSweepFraction
 PrintOopAddress
 ReflectionWrapResolutionErrors
 StarvationMonitorInterval
 ThreadSafetyMargin
 UseAltSigs
 UseBoundThreads
 UseCompilerSafepoints
 UseFastAccessorMethods
 UseFastEmptyMethods
 BackEdgeThreshold
 PreInflateSpin
Java HotSpot(TM) 64-Bit Server VM warning: Ignoring option
<Option>; support was removed in 9.0

Deprecated JVM Flags
126

Deprecated JVM Flags
 Two forms of warning message
127
warning[gc] -XX:+PrintGC is deprecated. Will use -Xlog:gc instead.
Java HotSpot(TM) 64-Bit Server VM warning: Option
CreateMinidumpOnCrash was deprecated in version 9.0 and will likely
be removed in a future release. Use option CreateCoredumpOnCrash
instead.

JVM Flags: Non-Starters (1)
128
 AdjustConcurrency
 CMSCompactWhenClearAllSoftRefs
 CMSDumpAtPromotionFailure
 CMSFullGCsBeforeCompaction
 CMSIncrementalDutyCycle
 CMSIncrementalDutyCycleMin
 CMSIncrementalMode
 CMSIncrementalOffset
 CMSIncrementalPacing
 CMSParPromoteBlocksToClaim
 CMSPrintEdenSurvivorChunks
 CollectGen0First
 GCLogFileSize
 NumberOfGCLogFiles
 ParallelGCVerbose
 PrintAdaptiveSizePolicy
 PrintCMSInitiationStatistics
 PrintCMSStatistics
 PrintClassHistogramAfterFullGC
 PrintClassHistogramBeforeFullGC
 PrintFLSCensus
 PrintFLSStatistics
 PrintGCApplicationConcurrentTime
 PrintGCApplicationStoppedTime
 PrintGCCause
 PrintGCDateStamps

JVM Flags: Non-Starters (2)
129
 PrintGCTaskTimeStamps
 PrintGCTimeStamps
 PrintHeapAtGC
 PrintHeapAtGCExtended
 PrintJNIGCStalls
 PrintOldPLAB
 PrintPLAB
 PrintParallelOldGCPhaseTimes
 PrintPromotionFailure
 PrintReferenceGC
 PrintTLAB
 PrintTenuringDistribution
 TraceDynamicGCThreads
 TraceGen0Time
 TraceGen1Time
 TraceMetadataHumongousAllocation
 TraceParallelOldGCTasks
 UseCMSCollectionPassing
 UseCMSCompactAtFullCollection
 UseGCLogFileRotation
 UseMemSetInBOT
 UsePPCLWSYNC
 UseVMInterruptibleIO
 WorkAroundNPTLTimedWaitHang

JVM Flags: Non-Starters
 50 command line flags from JDK 8
 Use will cause the JVM to abort at start
– It won't run your application
130
Unrecognized VM option '<Option>'
Error: Could not create the Java Virtual Machine.
Error: A fatal exception has occurred. Program will exit.

Real World Example

HdrHistogram Library
 Open source library (created by Gil Tene, Azul CTO)
 Ideally this should work with JDK 6, 7, 8 and 9 code
– Unchanged and with no special command line flags
 Problem:
– Needs to encode and decode using Base64
 Solutions:
– sun.misc.BASE64Encoder/Decoder (JDK 6, 7, 8)
– javax.xml.bind.DatatypeConverter (JDK 6, 7, 8)
– java.util.Base64.{Encoder,Decoder} (JDK 8, 9)
132

Solution
 Helper class with same named methods as from xml.bind
– printBase64Binary(byte[] array)
– parseBase64Binary(String input)
 Static code to determine which class is available
– Initialise Method object reference
 Helper methods invoke through method reference to
available implementation
133

Solution (1)
 Code in static block
try {
Class<?> javaUtilClass = Class.forName("java.util.Base64");
Method getDecoderMethod = javaUtilClass.getMethod("getDecoder");
decoderObj = getDecoderMethod.invoke(null);
decodeMethod = decoderObj.getClass().getMethod("decode", String.class);
Method getEncoderMethod = javaUtilClass.getMethod("getEncoder");
encoderObj = getEncoderMethod.invoke(null);
encodeMethod = encoderObj.getClass()
.getMethod("encodeToString", byte[].class);
} catch (Throwable e) { // ClassNotFoundException, NoSuchMethodException
decodeMethod = null;
encodeMethod = null;
}

Solution (2)
135
if (encodeMethod == null) {
decoderObj = null;
encoderObj = null;
try {
Class<?> xmlBindClass = Class.forName("javax.xml.bind.DatatypeConverter");
decodeMethod = xmlBindClass.getMethod("parseBase64Binary", String.class);
encodeMethod = xmlBindClass.getMethod("printBase64Binary", byte[].class);
} catch (Throwable e) {
decodeMethod = null;
encodeMethod = null;
}
}

JDK 10

Local Variable Type Inference
 At first sight, simple change
– Use var rather than explicit type declaration
– The compiler will infer the type for you
137
var list = new ArrayList<String>(); // infers ArrayList<String>
var stream = list.stream(); // infers Stream<String>

 var is now a reserved type
138
var var = new ArrayList<String>();
public class var {
public var(String x) {
...
}
}

 Very useful for intersection types
139
Stream<T> stream(Iterator<T>)
try (elements) {
Optional<String> first = stream(elements)
.findFirst(e -> e.startsWith("a"));
}
Closeable & Iterator elements; // COMPILER ERROR!
var elements; // CORRECTLY INFERED NON-DENOTABLE TYPE

 Non-denotable types
140
Object product = new Object() {
String name = "Widget";
int num= 20;
}
System.out.println("Name = " + product.name + ": " + product.num);
var product = new Object() {
String name = "Widget";
int num= 20;
}
System.out.println("Name = " + product.name + ": " + product.num);

JEP 307: Parallel Full GC for G1
 G1 is the default (server-class) collector since JDK 9
 Parallel collector performs full GC in parallel
 G1 full GC was single threaded
– Mark-Sweep-Compact
 Now performs full GC in parallel
 Number of threads is the same as used for rest of G1
– -XX:ParallelGCThreads
141

JEP 310: App Class-Data Sharing
 Strangely, only available on OpenJDK binary
– Not Oracle JDK (was a commercial feature)
 JVM startup requires classes to be loaded
– Same thing happens every time
 Application CDS effectively caches loaded classes
– Improved startup time for applications
– Can be shared between JVMs on same machine
142

Application CDS
143
java -Xshare:off
-XX:+UseAppCDS
-XX:DumpLoadedClassList=archive.list -cp zapp.jar Zapp
java -X:share:dump
-XX:+UseAppCDS
-XX:DumpLoadedClassList=archive.list
-XX:SharedArchiveFile=archive.jsa -cp zapp.jar
java -Xshare:on
-XX:+UseAppCDS
-XX:SharedArchiveFile=archive.jsa -cpzapp.jar Zapp

JEP 317: Graal JIT compiler
 Extend use of Graal to JIT compilation
 JIT compiler written in Java
– byte[] in, byte[] out
– We don't need a systems language like C++
– Made much simpler by JVMCI in JDK 9
 Part of Project Metropolis
 -XX:+UnlockExperimentalVMOptions -XX:+UseJVMCICompiler
144

JEP 319: Root Certificates
 The cacerts keystore file of OpenJDK was empty
– Things like TLS don't work without configuration
 Now has root certificates
– From providers in Oracle's Java SE root CA program
 17 root certificate providers
– Including Digicert, DocuSign, Comodo CA
145

JEP 296: Single Repo JDK
 JDK 9 and earlier had six separate repos
 root
 corba
 hotspot
 jaxp
 jaxws
 jdk
 langtools
 nashorn
 Problems like atomic commits across repos
– Now just one repo
146

JEP 316: Alternative Device Heap
 Some Non-Volatile RAM now as fast as DRAM
– Intel 3D XPoint
– Need to have same semantics as DRAM
 Safe atomic operations
 Existing heap related flags work unchanged
 Good for multi-JVM systems
– Select heap device appropriate to application
 -XX:AllocateHeapAt=<path>
147

JEP 304: GC Interface
 Most collector code lives in
– src/hotspot/share/gc/$NAME But not all (barriers,
etc)
 Extension to existing CollectedHeap class
 New collector must provide:
 A heap (sub-class of CollectedHeap)
 Barrier set (sub-class of BarrierSet)
 Implementation of CollectorPolicy, GCInterpreterSupport,
GCC1Support, GCC2Support
 Setup of a MemoryService
148

JEP 312: Thread-Local Handshake
 JVM performance enhancement
– Not accessible directly by developers
– Use a handshake (callback) rather than safepoint
– Pause one thread rather than all or none
 Example potential use cases
 Biased-lock revocation
 Deoptimisation
 External requests for stack traces
 Eliding memory barriers
149

JDK 10: APIs
 73 New APIs
– All methods
– No new classes
 Packages affected
– java.awt/javax.swing (!)
– java.io/nio/net
– java.lang
– java.time
– java.util
150

JDK 10: APIs
 New static methods on fundamental collection types
– List, Set, Map.copyOf(Collection)
151
List fixedList = List.copyOf(myList);

JDK 10: APIs
 Replacement for Optional.get()
– Optional.orElseThrow()
152
try {
Optional<MyType> result = getResult();
MyType value = result.orElseThrow();
} catch (NoSuchElementException nsee) {
System.out.println("No value in the optional");
}

JDK 10: APIs
– New Collectors
 toUnmodifiableList
 toUnmodifiableMap
 toUnmodifiableSet
153
List fixedList = data.stream()
.filter(dp -> dp.colourIsBlue())
.map(dp -> dp.getName())
.collect(Collectors.toUnmodifiableList());

JDK 10: Miscellaneous
 XMLInputFactory.newFactory() de-deprecated
(precated?)
 com.sun.security.auth package
– Six deprecated classes removed
 java.lang.SecurityManager
– One deprecated field and seven methods removed
154

JVM Container Support
 JVM now properly CGroup aware
 Initial values correctly calculated
– Heap sizing
– Thread pooling
155

Summary

Summary
 JDK 9 has many changes
 Java Platform Module System is the big one
– Migrating applications needs testing
 Other useful smaller features
 Removal of features and APIs a big change for Java
 JDK 10 first six-month development cycle
– Less changes
– Local variable type inference is useful
 Java continues to evolve!
157

Zulu Java
 Azul’s binary distribution of OpenJDK
– Passes all TCK tests
– Multi-platform (Windows, Linux, Mac)
– Free, with paid support options
– No licensing issues
– Verified as built from 100% open-source
 JDK 6, 7, 8 and 9
158
www.zulu.org/download

@speakjava
Thank you
Simon Ritter
Deputy CTO, Azul Systems
159

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