This document provides an overview of upcoming technologies beyond the Java Virtual Machine (JVM). It begins with introductions and then discusses several topics: - There are many open-source JVMs beyond Oracle's HotSpot such as JamVM, Maxine, and JikesRVM. - Reasons for using the JVM include its large standard library and ease of portability compared to alternative virtual machines. However, startup time can be slow. - Techniques for improving JVM startup time are discussed, such as saving JIT-compiled code and using the Drip tool to pre-initialize JVMs. - Native interoperability is explored through the Java Native Interface (JNI

1. Beyond JVM
A tour of upcoming technologies

2. Me
• Charles Oliver Nutter
• Red Hat (yes, I have one; no, I don’t wear it)
• JRuby and JVM languages
• JVM hacking and spelunking
• @headius

3. Goals
• Get you excited about the future of JVM
• Show you there are very few unsolvables
• Convince you to get involved

4. What is “JVM”?
• The JVM is software that runs JVM bytecode
• Java, Scala, Groovy, JRuby, Clojure, …
• OpenJDK contains Sun’s JVM “HotSpot”
• Oracle’s JDK is based on OpenJDK
• Many other JVMs exist for many platforms
• Some just replace HotSpot

5. OSS JVMs
•
•
•
•
•
•
•
•
•
Avian
Azul Zulu
CACAO
Dalvik
GCJ
HaikuVM
HotSpot
•
•
•
•
•
•
•
IcedTea
IKVM.NET
•
Jamiga
JamVM
Jaos
Jato VM
Jelatine JVM
JESSICA
Jikes RVM
(Jikes Research
Virtual
Machine)
JOP
•
•
•
•
•
•
•
•
•
Juice
Jupiter
JwiK
Kaffe
leDos
MateVM
Maxine
Mika VM
miniMV
•
•
•
•
•
Mysaifu
•
•
•
•
SuperWaba
NanoVM
RoboVM
SableVM
Squawk virtual
machine
TakaTuka
TinyVM.
VM02

6. Why JVM?

7. Why Not JVM?

10. Startup Time

13. Java-Heavy JDK
• + Less native code to maintain
• + Easier portability
• + Easier to swap out native side
• – Takes longer to warm up

14. Save JITed Code?
• Code will change across runs
• Often has specific memory addresses
• May optimize object layout differently
• Which JIT output?
• Client, Server, Tiered (1-4)

15. JRuby Startup
C Ruby
JRuby
JRuby (best)
-e 1
gem --help
rake -T
0
2.5
5
7.5
10

16. Drip
• Start a new JVM after each command
• Pre-boot JVM plus optional code
• Analyze command line for differences
• Age out unused instances
• https://github.com/flatland/drip

17. $ export JAVACMD=`which drip`
!
$ time jruby -e 1
!
real 0m1.655s
user 0m4.486s
sys 0m0.231s
!
system ~/projects/jruby $ time jruby -e 1
!
real 0m0.577s
user 0m0.052s
sys 0m0.065s

18. $ export DRIP_INIT_CLASS=org.jruby.main.DripMain
!
$ export DRIP_INIT=""
!
$ time jruby -e 1
!
real 0m0.580s
user 0m0.052s
sys 0m0.063s
!
system ~/projects/jruby $ time jruby -e 1
!
real 0m0.155s
user 0m0.049s
sys 0m0.058s

19. $ cat dripmain.rb
# Preload some code Rails always needs
require File.expand_path('../config/application', __FILE__)

20. JRuby Startup
C Ruby
JRuby (drip init)
JRuby (best)
JRuby (dripmain)
JRuby (drip)
-e 1
gem --help
rake -T
0
1.25
2.5
3.75
5

21. Native Interop

22. Native Interop

25. User Code
Java
JNI call
C/native
JNI impl
Target Library

26. JNI
public class GetPidJNI {!
public static native long getpid();!
!
public static void main( String[] args ) {!
getpid();!
}!
!
static {!
System.load(!
System.getProperty("user.dir") +!
"/getpidjni.dylib");!
}!
}

27. JNI
/* DO NOT EDIT THIS FILE - it is machine generated */!
#include <jni.h>!
/* Header for class com_headius_jnr_presentation_GetPidJNI */!
!
#ifndef _Included_com_headius_jnr_presentation_GetPidJNI!
#define _Included_com_headius_jnr_presentation_GetPidJNI!
#ifdef __cplusplus!
extern "C" {!
#endif!
/*!
* Class:
com_headius_jnr_presentation_GetPidJNI!
* Method:
getpid!
* Signature: ()J!
*/!
JNIEXPORT jlong JNICALL Java_com_headius_jnr_1presentation_GetPidJNI_getpid!
(JNIEnv *, jclass);!
!
#ifdef __cplusplus!
}!
#endif!
#endif

28. JNI
#include "com_headius_jnr_presentation_GetPidJNI.h"!
!
jlong JNICALL Java_com_headius_jnr_1presentation_GetPidJNI_getpid!
(JNIEnv *env, jclass c) {!
!
return getpid();!
}

29. JNI
$ gcc -I $JAVA_HOME/include -I
$JAVA_HOME/include/darwin -L
$JAVA_HOME/jre/lib/ -dynamiclib -ljava
-o getpidjni.dylib
com_headius_jnr_presentation_GetPidJNI.
c!
!
$ java -Djava.library.path=`pwd` -cp
target/jnr_presentation-1.0SNAPSHOT.jar
com.headius.jnr_presentation.GetPidJNI

30. Nobody enjoys calling
native libraries...

31. ...but if you have to call
native libraries, you
might as well enjoy it.

32. Java Native Runtime
• Java API
• for calling Native code
• supported by a rich Runtime library
• You may be familiar with JNA
• Foreign Function Interface (FFI)
• https://github.com/jnr
• Maven artifacts for everything

33. A Java API for binding
native libraries and
native memory

34. Justifications
• NIO, NIO.2
• Native IO, symlinks, FS-walking,
• Unmanaged memory
• Selectable stdio, process IO
• Low-level or other sockets (UNIX, ICMP, ...)
• New APIs (graphics, crypto, OS, ...)

35. User Code
Java
JNI call
C/native
JNI impl
Target Library

36. User Code
Java
JNI call
C/native
JNI impl
Target Library

37. User Code
JNR stub
Java
JNI call
C/native
JNI impl
libffi
Target Library

38. JNR
import jnr.ffi.LibraryLoader;!
import jnr.ffi.annotations.IgnoreError;!
!
public class GetPidJNRExample {!
public interface GetPid {!
long getpid();!
}!
!
public static void main( String[] args ) {!
GetPid getpid = LibraryLoader!
.create(GetPid.class)!
.load("c");!
!
getpid.getpid();!
}!
}

39. Layered Runtime
etc etc
jnr-posix
jnr-unixsocket!
jnr-enxio
jnr-constants
jnr-ffi
jffi
libffi
jnr-x86asm

40. JNR Platforms
• Darwin (OS X): universal (+ppc?)
• Linux: i386, x86_64, arm, ppc, ppc64, s390x
• Windows: i386, x86_64
• FreeBSD, OpenBSD: i386, x86_64
• SunOS: i386, x86_64, sparc, sparcv9
• AIX: ppc
• OpenVMS, AS/400: builds out there somewhere
• If your platform isn't here, contribute a build

41. jnr-ffi
• User-oriented API
• Roughly equivalent to what JNA gives you
• Functions, structs, callbacks, memory
• https://github.com/jnr/jnr-ffi

42. jnr-ffi
import jnr.ffi.LibraryLoader;!
import jnr.ffi.annotations.IgnoreError;!
!
public class GetPidJNRExample {!
public interface GetPid {!
long getpid();!
}!
!
public static void main( String[] args ) {!
GetPid getpid = LibraryLoader!
.create(GetPid.class)!
.load("c");!
!
getpid.getpid();!
}!
}

43. jnr-posix
• Pre-bound set of POSIX functions
• Mostly driven by what JRuby, Jython use
• Goal: 100% of POSIX bound to Java

44. public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
public
List<?
int chmod(String string, int i);!
int chown(String string, int i, int i1);!
int execv(String string, String[] strings);!
int execve(String string, String[] strings, String[] strings1);!
int fork();!
int seteuid(int i);!
int getgid();!
String getlogin();!
int getpgid();!
int getpgid(int i);!
int getpgrp();!
int getpid();!
int getppid();!
Passwd getpwent();!
Passwd getpwuid(int i);!
Passwd getpwnam(String string);!
Group getgrgid(int i);!
Group getgrnam(String string);!
int getuid();!
boolean isatty(FileDescriptor fd);!
int kill(int i, int i1);!
int symlink(String string, String string1);!
int link(String string, String string1);!
String readlink(String string) throws IOException;!
String getenv(String string);!
int setenv(String string, String string1, int i);!
int unsetenv(String string);!
int getpriority(int i, int i1);!
int setpriority(int i, int i1, int i2);!
int setuid(int i);!
FileStat stat(String string);!
int stat(String string, FileStat fs);!
int umask(int i);!
Times times();!
int utimes(String string, long[] longs, long[] longs1);!
int waitpid(int i, int[] ints, int i1);!
int wait(int[] ints);!
int errno();!
void errno(int i);!
int posix_spawnp(String string, List<? extends SpawnFileAction> list,
extends CharSequence> list1, List<? extends CharSequence> list2);

45. POSIX posix = POSIXFactory.getPOSIX(!
new MyPOSIXHandler(this),!
isNativeEnabled);

46. public interface POSIXHandler {!
public void error(Errno errno, String string);!
public void unimplementedError(String string);!
public void warn(WARNING_ID wrngd, String string, Object[] os);!
public boolean isVerbose();!
public File getCurrentWorkingDirectory();!
public String[] getEnv();!
public InputStream getInputStream();!
public PrintStream getOutputStream();!
public int getPID();!
public PrintStream getErrorStream();!
}

47. jnr-enxio
• Extended Native X-platform IO
• NIO-compatible JNR-backed IO library
• Read, write, select (kqueue, epoll, etc)
• Low-level fcntl control
• https://github.com/jnr/jnr-enxio

48. public class NativeSocketChannel!
extends AbstractSelectableChannel!
implements ByteChannel, NativeSelectableChannel {!
public NativeSocketChannel(int fd);!
public NativeSocketChannel(int fd, int ops);!
public final int validOps();!
public final int getFD();!
public int read(ByteBuffer dst) throws IOException;!
public int write(ByteBuffer src) throws IOException!
public void shutdownInput() throws IOException;!
public void shutdownOutput() throws IOException;!
}

49. jnr-unixsocket
• UNIX sockets for NIO
• Built atop jnr-enxio
• Fully selectable, etc
• https://github.com/jnr/jnr-unixsocket

50. How Does It Perform?

51. JNA getpid
JNR getpid
getpid calls, 100M times
100000ms
10000ms
1000ms
100ms
10ms
1ms

52. @IgnoreError
import jnr.ffi.LibraryLoader;!
import jnr.ffi.annotations.IgnoreError;!
!
public class GetPidJNRExample {!
public interface GetPid {!
@IgnoreError!
long getpid();!
}!
!
public static void main( String[] args ) {!
GetPid getpid = LibraryLoader!
.create(GetPid.class)!
.load("c");!
!
getpid.getpid();!
}!
}

53. JNR getpid
JNR getpid @IgnoreError
getpid calls, 100M times
2000ms
1500ms
1000ms
500ms
0ms

54. But There's More to Do
JNR getpid
JNI
JNR @IgnoreError
getpid calls, 100M times
2000ms
1500ms
1000ms
500ms
0ms
GCC -O3

55. JVM Help is Coming
• Standard FFI API in JDK
• JIT intelligence
• Drop JNI overhead where possible
• Bind native call directly at call site
• Security policies, segv protection, etc
• Time for an FFI JSR

56. Language Performance

57. History
• JVM authors mentioned non-Java languages
• Language authors have targeted JVM
• Hundreds of JVM languages now
• But JVM was a mismatch for many of them
• Usually required tricks that defeated JVM
optimizations
• Or required features JDK could not provide

58. What is
invokedynamic

59. JVM
Opcodes
Invocation
Field Access
invokevirtual!
invokeinterface!
invokestatic!
invokespecial
getfield!
setfield!
getstatic!
setstatic
Stack
Flow Control
Boolean and Numeric
Array Access
*aload!
*astore!
b,s,c,i,l,d,f,a
Local Vars
Allocation

60. Goals of JSR 292
• A user-definable bytecode
• Full freedom to define VM behavior
• Fast method pointers + adapters
• Optimizable like normal Java code
• Avoid future modifications

61. A User-definable
Bytecode
You decide how the JVM implements it
+
Method Pointers
and Adapters
Faster than reflection, with user-defined
argument, flow, and exception handling

62. invokedynamic opcode
user-def’d bytecode
method pointers
MethodHandles
invokedynamic

63. Method Invocation
VM Operations
Method Lookup
Type Checking
Branch
Method Cache
obj.foo()
Target
Object
JVM
Call Site
instanceof
Object’s
Class
void foo()
void foo()
static void bar()

64. // Static!
System.currentTimeMillis()!
Math.log(1.0)!
!
// Virtual!
"hello".toUpperCase()!
System.out.println()!
!
// Interface!
myList.add("happy happy")!
myRunnable.run()!
!
// Special!
new ArrayList()!
super.equals(other)

65. // Static!
invokestatic java/lang/System.currentTimeMillis:()J!
invokestatic java/lang/Math.log:(D)D!
!
// Virtual!
invokevirtual java/lang/String.toUpperCase:()Ljava/lang/String;!
invokevirtual java/io/PrintStream.println:()V!
!
// Interface!
invokeinterface java/util/List.add:(Ljava/lang/Object;)Z!
invokeinterface java/lang/Runnable.add:()V!
!
// Special!
invokespecial java/util/ArrayList.<init>:()V!
invokespecial java/lang/Object.equals:(java/lang/Object)Z

66. invokevirtual!
1. Confirm object is of correct type
2. Confirm arguments are of correct type
3. Look up method on Java class
invokestatic
4. Cache method
5. Invoke method
invokestatic!
1. Confirm arguments are of correct type
2. Look up method on Java class
3. Cache method
4. Invoke method
invokevirtual
invokeinterface!
1. Confirm object’s type implements interface
2. Confirm arguments are of correct type
3. Look up method on Java class
invokeinterface
4. Cache method
5. Invoke method
invokespecial!
1. Confirm object is of correct type
2. Confirm arguments are of correct type
3. Confirm target method is visible
4. Look up method on Java class
5. Cache method
6. Invoke method
invokespecial
invokedynamic!
1. Call your bootstrap code
2. Bootstrap wires up a target function
3. Target function invoked directly until you change it

67. invokedynamic bytecode
target method
bo
ot
st
ra
p
m
et
ho
d
method handles

68. How Do You Benefit?

69. Indy Languages
• New language impls
• JavaScript: Dyn.js and Nashorn
• Redline Smalltalk
• Improved language performance
• JRuby, Groovy, Jython
• Java features too!

70. JRuby/Java 6
JRuby/Java 7
Times Faster than Ruby 1.9.3
5
4.32
3.75
3.66
3.44
2.5
2.658
1.914
1.25
0
1.346
base64
1.565
1.538
richards
neural
redblack

71. red/black tree, pure Ruby versus native
ruby-2.0.0 + Ruby
2.48s
ruby-2.0.0 + C ext
0.51s
jruby + Ruby
0.29s
0
0.75
1.5
Runtime per iteration
2.25
3

72. Indy + JNR
Ruby getpid
Java getpid
100M getpid calls
2700
2025
1350
675
0

73. Caveat Emptor
• Indy was really slow in first Java 7 release
• Got fast in 7u2...and turned out broken
• Rewritten for 7u40
• Slow to warm up
• Still some issues (memory use, etc)
• Java 8 due in March…

74. All That C++

75. JVM
Language
JVM
Bytecode
Out of our control
Written in C++
Bytecode
Interpreter
Bytecode
JIT
Native
Code

76. What If…
• The JVM’s JIT optimizer were written in Java
• You could customize how the JIT works for
your language or library
• JITed code could directly make native calls

77. Graal
• A 100% Java-based JIT framework
• Grew out of the 100% Java “Maxine” JVM
• Backends to assembly or HotSpot IR
• Directly control code generation
• Build a language without using JVM bytecode
• http://openjdk.java.net/projects/graal/

78. JVM
Language
Plain Java APIs
Graal
Intermediate
Representation
Graal
Optimizer
Under your control
Your
Transformations
Your
Optimizations
Native
Code

79. However…
• Not everyone is a compiler writer
• Graal’s IR is low-level and nontrivial
• Need to understand JVM internals
• Need some understanding of CPU

80. The Dream
• Design your language
• ???
• PROFIT

81. Typical JVM Language
• Design your language
• Maybe write an interpreter
• Compile to JVM bytecode
• Pray that the JVM optimizes it right
• PROFIT

82. What We Want
• Design your language
• Write an interpreter
• PROFIT

83. Truffle
• Language framework built on Graal
• Designed to fulfill the dream
• Implement interpreter
• Truffle feeds that to backend
• No compiler expertise needed
• https://wiki.openjdk.java.net/display/Graal/Truffle+FAQ+and+Guidelines

84. JVM
Language
Truffle
AST
All we need
Graal
Intermediate
Representation
Graal
Optimizer
Native
Code

87. The Final Word
• JVM is a powerful platform
• Java and other languages are evolving
• The JVM is adapting to our needs
• New tools breaking JVM’s boundaries

88. Thank you!
• Charles Oliver Nutter
• @headius, headius@headius.com
• http://blog.headius.com