A Post-Apocalyptic sun.misc.Unsafe World

http://www.superbwallpapers.com/fantasy/post-apocalyptic-tower-bridge-london-26546/
A Post-Apocalyptic
sun.misc.Unsafe
World

www.hazelcast.com@noctarius2k
Disclaimer
This talk is not going to be negative!

Who’s that dude?
• Chris Engelbert
• Manager of Developer Relations @Hazelcast
• Java-Passionate (10+ years)
• Performance
• Garbage Collection
• Benchmark Fairytales

sun.misc.Unsafe?

sun.misc.Unsafe?
dangerous
low level
discourage
performance
platform speciﬁc
pointers
UNSAFE

sun.misc.Scissors

“My precious.”

“My precious.”The Lord of the Rings

Internal Class of the JDK

Internal Class of the JDK
and those are not intended for outside use :)

Used inside and outside the JDK / JRE
custom (64-bit)
memory allocation
fast
memory access
fast
(de)serialization
minimizegc overhead
custom
memory fences
efﬁcientmemory layout
(array element)
volatile semantics

// Unsafe mechanics 
private static final sun.misc.Unsafe U; 
private static final long QBASE; 
private static final long QLOCK; 
private static final int ABASE; 
private static final int ASHIFT; 
static { 
try { 
U = sun.misc.Unsafe.getUnsafe(); 
Class<?> k = WorkQueue.class; 
Class<?> ak = ForkJoinTask[].class; 
QBASE = U.objectFieldOffset 
(k.getDeclaredField("base")); 
QLOCK = U.objectFieldOffset 
(k.getDeclaredField("qlock")); 
ABASE = U.arrayBaseOffset(ak); 
int scale = U.arrayIndexScale(ak); 
if ((scale & (scale - 1)) != 0) 
throw new Error("data type scale not a power of two"); 
ASHIFT = 31 - Integer.numberOfLeadingZeros(scale); 
} catch (Exception e) { 
throw new Error(e); 
} 
} 
}
example:
java.util.concurrent.ForkJoinPool

“I’m the kind of the world!”

“I’m the kind of the world!”Titanic

#
# A fatal error has been detected by the Java Runtime Environment:
#
# SIGSEGV (0xb) at pc=0x00000001067314b5, pid=25244, tid=5891
#
# JRE version: Java(TM) SE Runtime Environment (8.0_05-b13) (build 1.8.0_05-b13)
# Java VM: Java HotSpot(TM) 64-Bit Server VM (25.5-b02 mixed mode bsd-amd64 compressed oops)
# Problematic frame:
# V [libjvm.dylib+0x5314b5] Unsafe_SetNativeAddress+0x36
#
# An error report ﬁle with more information is saved as:
# /Users/noctarius/git/hazelcast-only.idea/hs_err_pid25244.log
#
# If you would like to submit a bug report, please visit:
# http://bugreport.sun.com/bugreport/crash.jsp
#

“Supercalifragilisticexpialidocious!”

“Supercalifragilisticexpialidocious!”Mary Poppins

MapDB
Netty
Hazelcast
Cassandra Mockito
EasyMock
JMock
Scala
Robolectric
Grails
GsonNeo4j
Apache Ignite
Apache Spark
Apache Kafka
Apache Storm
Apache Continuum
Zookeeper
Dropwizard
Kryo
Byte Buddy
Hibernate
Liquibase
Spring Framework
Ehcache
OrientDB
Chronicle
Apache Hadoop
Apache HBase GWT
Disruptor
JRubyAkka
Agrona
Aeron
Simple Binary Encoding
XRebel
Presto
jol
LWJGL
XAP
XStream
CapLogic
WildFly
Inﬁnispan

Hazelcast Use Cases

Hazelcast Use Cases
custom (64-bit)
memory allocation
fast
memory access
fast
(de)serialization
minimize
gc overhead
custom
memory fences
efﬁcientmemory layout
(array element)
volatile semantics

“There’s no place like home.”

“There’s no place like home.”The Wizard of Oz

Close ;-)
Language URL sun.misc.Unsafe
Avian C++ https://github.com/ReadyTalk/avian Yes
BicaVM JavaScript https://github.com/nurv/BicaVM No
Cacao C http://www.cacaojvm.org Yes
Excelsior JVM C / C++ ? http://www.excelsiorjet.com Yes
Dalvik / ART / Android C / C++ https://source.android.com/source/index.html Yes
Graal mainly Java http://openjdk.java.net/projects/graal Yes
GCJ C / C++ https://gcc.gnu.org/java Yes
HaikuVM C http://haiku-vm.sourceforge.net No
IBM J9 C / C++ ? http://www.ibm.com/developerworks/java/jdk/index.html Yes
IcedTea C / C++ http://icedtea.classpath.org/wiki/Main_Page Yes
IKVM.NET C# http://www.ikvm.net Yes
Jamiga C https://sourceforge.net/projects/jamiga2 No
JamVM C http://jamvm.sourceforge.net Yes
JatoVM C http://jatovm.org Yes
JikesRVM C microkernel, Java http://www.jikesrvm.org Yes
JNode C microkernel, Java http://www.jnode.org Yes
JVM.go Go https://github.com/zxh0/jvm.go Yes
JX C http://www4.cs.fau.de/Projects/JX/index.html No
Kaffe C https://github.com/kaffe/kaffe Yes
NanoVM C http://harbaum.org/till/nanovm/index.shtml No
OpenJDK / Oracle / Zulu C / C++ http://openjdk.java.net Yes
RoboVM C / C++ / ObjC https://robovm.com Yes
SAPJVM C / C++ ? http://help.sap.com/saphelp_nwce10/helpdata/en/47/
dc90b4ef17452289f9128b8c2bbd77/content.htm
Yes
Waratek Multitenant JVM C / C++ ? http://www.waratek.com Yes
Zing JVM C / C++ ? https://www.azul.com/products/zing Yes

“To inﬁnity and beyond!”

“To inﬁnity and beyond!”Toy Story

http://mail.openjdk.java.net/pipermail/openjfx-dev/2015-April/017028.html
Let me be blunt -- sun.misc.Unsafe must die in a ﬁre. It is -- wait
for it -- Unsafe. It must go. Ignore any kind of theoretical rope and
start the path to righteousness _*/now/*_. It is still years until the
end of public updates to JDK 8, so we have /*years */to work this out
properly. But sticking our heads in the collective sands and hoping for
trivial work arounds to Unsafe is not going to work. If you're using
Unsafe, this is the year to explain where the API is broken and get it
straight....
Please help us kill Unsafe, kill Unsafe dead, kill Unsafe right, and do
so as quickly as possible to the ultimate beneﬁt of everyone.
Wed Apr 8 19:15:42 UTC 2015, OpenJFX Mailinglist, Donald Smith, Oracle

Oracle created a new Taskforce

Oracle created a new Taskforce
K.U.T.T. - Kill Unsafe To Total death

https://docs.google.com/document/d/1GDm_cAxYInmoHMor-AkStzWvwE9pw6tnz_CebJQxuUE
Hazelcast
jClarity
Azul Systems
Higher Frequency Trading
Rafael Winterhalter
Richard Warburton
and many others…

Mutation: it is the key to our evolution.

Mutation: it is the key to our evolution.
X-Men

Problem 1: Get Access

Unsafe unsafe = Unsafe.getUnsafe();
Easy One (not working outside the JRE / JDK)

private static final Unsafe UNSAFE; 
static { 
try { 
Field theUnsafeField = Unsafe.class.getDeclaredField("theUnsafe"); 
theUnsafeField.setAccessible(true); 
UNSAFE = (Unsafe) theUnsafeField.get(Unsafe.class); 
 
// We need you! =( 
} 
}
The Ugly One

Problem 1: Get Accessprivate static Unsafe findUnsafe() { 
try { 
return Unsafe.getUnsafe(); 
} catch (SecurityException se) { 
return AccessController.doPrivileged(new PrivilegedAction<Unsafe>() { 
@Override 
public Unsafe run() { 
try { 
Class<Unsafe> type = Unsafe.class; 
try { 
Field field = type.getDeclaredField("theUnsafe"); 
field.setAccessible(true); 
return type.cast(field.get(type)); 
 
for (Field field : type.getDeclaredFields()) { 
if (type.isAssignableFrom(field.getType())) { 
field.setAccessible(true); 
return type.cast(field.get(type)); 
} 
} 
} 
throw new RuntimeException("Unsafe unavailable", e); 
} 
throw new RuntimeException("Unsafe unavailable"); 
} 
}); 
} 
}
The Hazelcast One
(also working in most other JVMs)

The Tricky One
private static final Unsafe UNSAFE; 
static { 
try { 
Constructor<Unsafe> constructor =
Unsafe.class.getDeclaredConstructor();
 
constructor.setAccessible(true); 
UNSAFE = constructor.newInstance(); 
 
// We need you! =( 
} 
}

Does Any Of This Feel Right?

Weird!
No!

WAAAAAT!?!?
No!

Solution 1: Get Access

Solution 1: Get Access
Nothing; not needed anymore!

Problem 2: Atomic Updates
private static final Unsafe UNSAFE = findUnsafe();
private static long VERSION_OFFSET = findVersionOffset();
// Updated through Unsafe only!
private volatile long version = 0;
public long increment() {
while(true) {
long version = this.version;
long newVersion = version + 1;
if (UNSAFE.compareAndSwapLong(
this, VERSION_OFFSET, version, newVersion)) {
return newVersion;
}
}
}
Going Unsafe

We can do better! There’s an API already!

private final AtomicLong version = new AtomicLong(0);
public long increment() {
return version.incrementAndGet();
}
We can do better! There’s an API already!
But one AtomicLong instance per version

We can still do better! There’s yet another API already!

private static final AtomicLongFieldUpdater<Record> VERSION = 
AtomicLongFieldUpdater.newUpdater(Record, "version"); 
// Updated through atomic field updater only! 
private volatile long version = 0; 
 
public long increment() { 
return VERSION.incrementAndGet(this); 
}

Solution 2: Atomic Updates
private static final AtomicLongFieldUpdater<Record> VERSION = 
AtomicLongFieldUpdater.newUpdater(Record, "version"); 
// Updated through atomic field updater only! 
 
return VERSION.incrementAndGet(this); 
}
You guessed it, __ uses it ;-)

private static final VarHandle VERSION = findVersionVarHandle(); 
 
// Updated through VarHandle only! 
 
return (long) VERSION.addAndGet(this, 1); 
}
JVM can inline those calls

public static VarHandle findVersionVarHandle() { 
try { 
return MethodHandles.lookup(). 
findFieldVarHandle(Record.class, "version", long.class); 
 
} 
}
Statically cache the VarHandle instance

Problem 3: Memory Management
public long memory() { 
long address = UNSAFE.allocateMemory(8);
 
UNSAFE.putLong(address, Long.MAX_VALUE);
 
return UNSAFE.getLong(address); 
}
Keyword: Off-Heap

Problem 3: Memory Management
ByteBuffer possible; API is 32bit though
ByteBuffer byteBuffer = ByteBuffer.allocateDirect(8); 
 
byteBuffer.putLong(0, Long.MAX_VALUE); 
 
return byteBuffer.getLong(0); 
}

Solution 3: Memory Management
ByteBuffer byteBuffer = ByteBuffer.allocateDirect(8); 
 
VarHandle bufferView = 
MethodHandles.byteBufferViewVarHandle(long[].class, true); 
 
bufferView.set(byteBuffer, 0, Long.MAX_VALUE); 
 
return bufferView.get(byteBuffer, 0); 
}
Simpliﬁes off-heap implementations, 
empowers new ideas

Solution 3.5: Memory Management
Even easier to build a great off-heap
public long memory(long index) { 
try (Scope scope = new NativeScope()) { 
Pointer<Long> ptr = scope.allocate( 
NativeLibrary.createLayout(long.class), numElements); 
 
Reference<Long> ref = ptr.offset(index).deref(); 
 
ref.set(Long.MAX_VALUE); 
 
return ref.get(); 
} 
}

Problem 4: Serialization
private static final Unsafe UNSAFE = findUnsafe(); 
 
private static final long VALUE_OFFSET = findValueOffset(); 
 
public String deserializeString() throws Exception { 
char[] chars = magicallyDecodeUTF8FromStream(); 
String allocated = (String) UNSAFE.allocateInstance(String.class); 
UNSAFE.putObjectVolatile(allocated, VALUE_OFFSET, chars); 
return allocated; 
}

Problem 4: Serialization
private static final Unsafe UNSAFE = findUnsafe(); 
 
private static final long VALUE_OFFSET = findValueOffset(); 
 
String allocated = (String) UNSAFE.allocateInstance(String.class); 
UNSAFE.putObjectVolatile(allocated, VALUE_OFFSET, chars); 
return allocated; 
}
Will break in Java 9 (compressed Strings)

Solution 4: Serialization
 
ReflectionFactory reflectionFactory = 
ReflectionFactory.getReflectionFactory(); 
 
Constructor<String> constructor = reflectionFactory 
.newConstructorForSerialization(String.class, char[].class); 
 
return constructor.newInstance(chars); 
}
sun.reflect.ReflectionFactory -> java.lang.reflect.ReflectionFactory (or similar)

Problem 5: Native Interoperability
extern c { 
JNIEXPORT int JNICALL 
Java_ProcessIdentifier_getProcessId(JNIEnv *, jobject); 
} 
 
Java_ProcessIdentifier_getProcessId(JNIEnv *env, jobject thisObj) { 
return getpid(); 
} 
 
public class ProcessIdentifier { 
static { 
System.loadLibrary("processidentifier"); 
} 
 
public native void getProcessId(); 
}

Problem 5: Native Interoperability
extern c { 
Java_ProcessIdentifier_getProcessId(JNIEnv *, jobject); 
} 
 
Java_ProcessIdentifier_getProcessId(JNIEnv *env, jobject thisObj) { 
return getpid(); 
} 
 
public class ProcessIdentifier { 
static { 
System.loadLibrary("processidentifier"); 
} 
 
public native void getProcessId(); 
}
Fortunately we don’t deal with it, but who loves it anyways ;-)

Solution 5: Native Interoperability (for now)
interface LibC { 
void getpid(); 
} 
 
public int call() { 
LibC c = LibraryLoader.create(LibC.class).load("c"); 
return c.getpid(); 
}
JNR, but guess what it uses internally ;-)

Solution 5: Native Interoperability
public void call() {
MethodType intType = MethodType.methodType(int.class);
 
MethodHandle handle = MethodHandles 
.findNative(null, “getpid”, intType);
 
return (int) handle.invokeExact(); 
}
They inline … just ﬁne.

Problem 6: Immutable Types
Defensive Copies, no real optimization yet

Solution 6: Immutable Types
value class Point { 
final int x; 
final int y; 
} 
 
// Create a Point instance 
Point point = makeValue(1, 2);
Value Types

int[] values = new int[2]; 
int x = values[0]; 
int y = values[1];
Looks like
final int x; 
final int y; 
} 
 
Value Types

final int x; 
final int y; 
} 
 
Value Types
int[] values = new int[2]; 
int x = values[0]; 
int y = values[1];
Stack
var X
var Y
Looks like
Stack Allocation!

Problem 7: Generics
HazelcastInstance client = HazelcastClient.newHazelcastClient();
Map<Long, String> messages = client.getMap("messages");
String message = messages.get(1234L);
No generics on primitives

Problem 7: Generics
HazelcastInstance client = HazelcastClient.newHazelcastClient();
Map<Long, String> messages = client.getMap("messages");
String message = messages.get(1234L);
No generics on primitives
Auto-(Un)Boxing

Solution 7: Generics
class Box<any T> { 
void set(T element) { ... };
 
T get() { ... }; 
}
Specialized Generics (yeah it’s kind of a template)

class Box<any T> { 
void set(T element) { ... };
 
T get() { ... }; 
}
Specialized Generics (yeah it’s kind of a template)
Box<int> Box${T=int}.class 
Box<String> Box${T=java.lang.String}.class 
Box<RandomClass> Box${T=RandomClass}.class

public void generics() { 
List<int> intList = client.getList("foo"); 
intList.add(1); 
int intValue = intList.get(0); 
 
Queue<String> stringQueue = client.getQueue("foo"); 
stringQueue.offer("hello"); 
String stringValue = stringQueue.poll(); 
 
Map<int, String> messages = client.getMap("messages"); 
messages.put(1234L, "hello"); 
String message = messages.get(1234L); 
}

Arrays 2.0
int[] values = new int[Long.MAX_VALUE];

Arrays 2.0
Arrays.chop(T[] a, int newlength);

Arrays 2.0
Box<String>[] ... = new Box<String>[];

Arrays 2.0
Box<int>[] ... = new Box<int>[];

Arrays 2.0
Box<int>[] ... = new Box<int>[];
char[] frozen = new char[20L].freeze();

Cleaner API
package java.nio;
import sun.misc.Cleaner;
class DirectByteBuffer 
extends MappedByteBuffer 
implements DirectBuffer {
private static class Deallocator implements Runnable {
private Deallocator(long address, long size, int capacity) {...}
public void run() {...}
}
private final Cleaner cleaner;
DirectByteBuffer(int cap) {
...
cleaner = Cleaner.create(this, new Deallocator(base, size, cap));
}
}

Cleaner API
public selfCleaning() { 
try(AutoCleaning autoCleaning : new AutoCleaning()) { 
// do your thing here 
} 
}

Cleaner API
public class AutoCleaning implements AutoCloseable {
// A cleaner, preferably one shared within a library
private static final Cleaner cleaner = ...;
static class State
implements Runnable {
State(...) {/* initialize State needed for cleaning action */}
public void run() {/*cleanup action accessing State, executed at most once*/}
}
private final State state;
private final Cleaner.Cleanable cleanable;
public AutoCleaning() {
this.state = new State(...);
this.cleanable = cleaner.register(this, state);
}
public void close() {
cleanable.clean();
}
}

Class Dynamic
• Templating functionality

Class Dynamic
• Aspect-like approach

Class Dynamic
• Group common functionality

Class Dynamic
• Enhanced Proxies
R methodName(ARGS) { 
synchronized (this) { 
underlying.methodName(ARGS); 
} 
}
Collections::sychronizedMap

Class Dynamic
• Enhanced Proxies
Logging / Tracing
R methodName(ARGS) { 
logger.trace("Before methodname X");  
underlying.methodName(ARGS); 
logger.trace("After methodname X"); 
}

What Else?
No idea!
A lot is changing now.
Java / JVM will be different.
… but lots of interesting features, not only for us :)

What Else?
Don’t forget about Jigsaw,
test your application with Java 9 EA builds!
https://jdk9.java.net/jigsaw/

“My mama always said, ‘Life was like a box of
chocolates. You never know what you’re gonna get.”

“My mama always said, ‘Life was like a box of
chocolates. You never know what you’re gonna get.”
Forrest Gump

Thank You!
Any Questions?
@noctarius2k
http://www.sourceprojects.org
http://github.com/noctarius
@hazelcast
http://www.hazelcast.com
http://www.hazelcast.org
http://github.com/hazelcast

More information:
• http://openjdk.java.net/jeps/193
• http://openjdk.java.net/projects/valhalla/
• http://cr.openjdk.java.net/~jrose/arrays/frozen-array-value-rules.html
• https://twitter.com/PaulSandoz/status/623891528432394240
• http://openjdk.java.net/projects/panama/
• http://cr.openjdk.java.net/~jrose/values/values-0.html
• http://cr.openjdk.java.net/~briangoetz/valhalla/spec-classdyn.html
• http://blog.codefx.org/java/dev/the-road-to-valhalla/
Thank You!

Thank You!
http://openjdk.java.net/jeps/259

A Post-Apocalyptic sun.misc.Unsafe World

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