JRuby: Pushing the Java Platform Further

Pushing the Java Platform
Further

Me

Charles Oliver Nutter
● headius@headius.com
● @headius
● JRuby co-lead, fulltime since 2006
● JVM enthusiast
● http://blog.headius.com

JRuby

● Ruby atop the JVM
○ "Just another Ruby implementation"
○ "Just another JVM language"
● A challenge for the JVM
○ Dynamic typing/dispatch
○ Own set of core classes
○ Heavy use of OS-level features

What Classes?

● Array: a mutable, growable list of objects
● Hash: an ordered associative collection
● String: a collection of bytes (w/ an encoding in 1.9)
● Symbol: a named identifier
● IO: a stream of bytes (w/ an encoding in 1.9)
● File: a stream of bytes from filesystem
● Range: a range of values

Why Custom?

● Array, Hash
○ Behavior must match Ruby exactly
○ Many operations must redispatch into Ruby
● String
○ Java's String is immutable
○ Java's String is UTF-16 char[] based
● Regexp
○ byte[] based String necessitates it
○ Ruby Regexp is rich in features
● IO, File
○ Blocking IO simulated atop non-blocking
○ No good abstractions over NIO

String

● Used for both binary and character data
○ "It's just bytes"
○ IO operations receive, return String
● Arbitrary encoding
○ Implicit encoding in 1.8 (set globally)
○ Explicit encoding in 1.9 (String aggregates Encoding)
● Mutable
○ More efficient to mutate in-place
○ Copy-on-write to reduce object churn

ByteList

http://github.com/jruby/bytelist

ByteList

● A list of bytes
○ Abstraction around byte[] + encoding
○ Similar operations to StringBuffer
○ CoW-capable

Regexp

● Operates against byte[] in String
○ All other engines operate against char[]
○ Transcoding cost == death
● Supports arbitrary encoding
○ Not all encodings transcode losslessly
○ Mismatched but compatible encodings?
● Bytecode engine
○ Avoids StackOverflow bugs in java.util.regex
○ Optimization potential
● Advanced regex features
○ Encoding-agnostic
○ Named groups

Joni

http://github.com/jruby/joni

Joni

● Java port of Oniguruma
● Ruby-friendly
○ byte[] based
○ Arbitrary encodings
○ Bytecoded engine
● Fast
○ Avoids transcoding costs
○ Sometimes faster than j.u.regex

Thanks to Marcin Mielzynski (github.com/lopex)!

OS-level Features

● Process management
○ getpid, waitpid, kill, signal, ...
● Filesystem operations
○ symlink, ownership, permissions, ...
● User-friendly IO
○ Interruptible, inherit TTY, "select" function, ...
● Binding native libs
○ Avoid hand-written native shim (JNI)
○ Route around JVM APIs
● UNIX sockets

Java Native Runtime

http://github.com/jnr

Java Native Runtime

A collection of libraries to make interfacing with OS-level
features easier.

● Easy binding of native libs
● NIO-like IO atop file descriptors
● UNIX sockets
● POSIX filesystem operations

Big thanks to Wayne Meissner (@wmeissner)!

JNR-FFI
(foreign function interface)
http://github.com/jnr/jnr-ffi

JNR-FFI

● Base of the JNR libraries
● Easy binding of native functions
● Struct mapping
● Memory/pointer management
● As fast as JNI?
○ Within 10-20% (comparing invocation overhead)
○ "a viable alternative, even for reasonably
performance-sensitive libraries" - @wmeissner
○ "A hell of a lot nicer than using JNI!" - @headius

JNR-POSIX

http://github.com/jnr/jnr-posix

JNR-POSIX

● Commonly used POSIX functions not in JDK
○ Symlinks
○ Filesystem metadata
○ Ownership, permissions
○ True "exec"
○ Process management

JNR-ENXIO
(Extended Native X-platform IO)
http://github.com/jnr/jnr-enxio

JNR-ENXIO

● Mimics NIO
○ Same or similar API
○ Channels, Selectors, etc
● Implemented atop JNR-FFI
○ 100% Java (other than JNR-FFI)
● Multiple backends
○ poll, kqueue currently
○ epoll, win32 needed...volunteers?
● Full set of operations for *any* IO type
○ NIO can't select on stdio, files

JNR-UNIXSOCKET

http://github.com/jnr/jnr-unixsocket

JNR-UNIXSOCKET

● Built atop jnr-enxio
● UNIX sockets
○ Need I say more?

JNR-X86ASM
(yes, it's what you think)
http://github.com/jnr/jnr-x86asm

JNR-X86ASM

● API for x86/x86_64 ASM generation
● Huh?
○ Down to the metal, baybee
○ Faster bindings to native functions
○ Other weird stuff...

Ruby FFI

http://github.com/ffi/ffi

Ruby FFI

● Ruby DSL for binding native libraries
● Cross-impl
○ Supported on JRuby and standard Ruby
● Fun!

What Have We Learned?

● The JVM can be a great native platform
● No problem is impossible to solve ;-)
● JRuby gives you all this (and more) for free

Links and Q/A

(All on Github)
http://github/
● jruby - JRuby organization
○ /jruby - JRuby itself
○ /bytelist - byte[] container
○ /jcodings - byte[] encoding support
○ /joni - byte[] regex
● /jnr - Java Runtime
○ /jnr-ffi - foreign function interface
○ /jnr-posix - POSIX features
○ /jnr-enxio - native IO
○ /jnr-unixsocket - UNIX sockets
○ /jnr-x86asm - x86 assembly
● /ffi/ffi - Ruby FFI

JRuby: Pushing the Java Platform Further

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