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Tackling the OpenJDK can be intimidating.Therefore, let's....** figure out what's in the OpenJDK** discover how to build** examine the layout of the OpenJDK sources** make a trivial(!) change and build
My goal is not to teach you all of the OpenJDK-- no way I can do that in just one lectureMy goal is to teach you enough that you can start learning-- in other words, get you started, then shove you out of the nest
In order to make the most of this talk, you should...** be comfortable with C++--- really really helps to be comfortable with JNI** be (very very!) comfortable with Java** understand that this is a large (millions of lines) codebase--- large codebases do things a little differently** have a fast machine with lots of RAM, disk space, and a fat pipe
In the beginning...** Java was a closed-source, proprietary system--- sort of
Back in the earliest days of Java (JDK 1.0.2)** you could download an unofficial source build** but it was*** unsupported*** unbuildable (for the most part)*** unpatchable** in a nutshell, it wasn't officially "open source"This held true for all versions of Java before Java5
This non-FOSS arrangement was not popular** several Java alternatives emerged:*** Project Classpath*** IcedTea*** ... and a few other coffee puns** IBM started an OSS JVM: Harmony--- several, actually, including a JVM-written-in-Java (Jikes RVM)** a few others explored the idea
Note that the sources were available, just not free** Sun sold source licenses of the JDK code** Microsoft was one such licensee** Sun maintained a distinction between "spec" and "implementation"
Java5: Time to go open-source!
Java5: Time to go open-source!** much, much easier said than done** required total modernization of the tools--- particularly for Windows builds** required storage in OSS repositories--- they chose Mercurial** required acceptance of outside patches--- which they didn't, at first** required FOSS-equivalents to non-FOSS components--- TrueType fonts, video and audio codecs, and so on
Java6: Almost there** by the time Java6 shipped, Sun had almost gotten everything done*** Windows build tooling were mostly up-to-date*** outside commitments slowly being integrated** but problems still remained--- namely, all those non-FOSS equivalents** so "OpenJDK" became another JVM implementation** as opposed to "Sun" (or soon, "Oracle") JDK
This bifurcation remains true today** OpenJDK: completely open-source** OracleJDK: technically commercial and closed-source--- but derives from OpenJDK source base** ... and this will probably remain true forever--- or at least as long as those non-FOSS components are in use
OpenJDK is a mix of Java and C++ source** much of the code is Java--- various java., javax. packages, some of which have native methods** "core" native code bits are Hotspot--- garbage collectors, JIT, threading, and so on** "servicability" bits are mixed native/Java--- JMX, instrumentation, etc** "langtools" (compilers, etc) are almost all Java
Release pages:** JDK 6--- http://openjdk.java.net/projects/jdk6/** JDK 7--- http://openjdk.java.net/projects/jdk7/** JDK 8--- http://openjdk.java.net/projects/jdk8/
Note that JDK 'updates' are a different project!** for gnarly legal and licensing reasons** JDK 7u--- updates to the JDK 7 project** JDK 8u--- updates to the JDK 8 project** all development has closed down on the non-update repositories!--- I am going to assume you don't care about pre-8u sources
Building OpenJDK 8u** Clone the root repo--- hg clone http://hg.openjdk.java.net/jdk8u/jdk8u** Pull the "dependent" source trees--- cd jdk8u; bash get_source.sh
Source layout** a "root project" with several "subprojects"** technically this is a Mercurial "forest"--- but that's really complicated, so they simplified by adding the get_source script** subprojects:*** corba*** hotspot*** jaxp*** jaxws*** jdk*** langtools*** nashorn
Source layout** within each subproject, usually a "make" and "src"--- sometimes a "test" directory** "make" typically is black-box build stuff** "src" usually breaks down into*** platform-specific ("windows", "share")*** Java- vs native ("classes" vs not "classes")*** and for "classes", the usual package-qualified breakdown
Configure the makefiles** run the "configure" script to configure all the makefiles--- bash configure** note that any missing dependencies will be flagged and configure will terminate** check out ./README-builds.html for build details
Requirements** All:*** a "boot JDK" installation for Java files compilation*** generally the boot JDK must be one version behind (JDK 7)** MacOS:--- Xcode 4 (!) and command-line tools** Windows:*** Visual Studio 2013*** Cygwin (for Unix-style build chain)** Linux:--- usual build chain (g++, etc)
Release page:** JDK 9--- http://openjdk.java.net/projects/jdk9/** big change:--- complete project restructure for modules
Building OpenJDK 9:** Clone root repo:--- hg clone http://hg.openjdk.java.net/jdk9/jdk9** Pull the "dependent" source trees--- cd jdk9; bash get_source.sh
Source layout** a "root project" with several "subprojects"** technically this is a Mercurial "forest"--- but that's really complicated, so they simplified by adding the get_source script** subprojects:*** corba*** hotspot*** jaxp*** jaxws*** jdk*** langtools*** nashorn
Source layout** within each subproject, usually a "make" and "src"--- sometimes a "test" directory** "make" typically is black-box build stuff** "src" usually breaks down into*** java modules ("java.desktop", "java.rmi", etc)*** or os-specific ("bsd", "solaris", "windows", etc)** within each module, breaks down into*** "share" (os-independent) or os-specific*** "classes" (Java) v "native" (C++)
Configure the makefiles** run the "configure" script to configure all the makefiles--- bash configure** note that any missing dependencies will be flagged and configure will terminate** check out ./README-builds.html for build details
Requirements** All:*** a "boot JDK" installation for Java files compilation*** generally the boot JDK must be one version behind (JDK 7)** MacOS:--- XCode and command-line tools** Windows:*** Visual Studio 2015*** Cygwin (for Unix-style build chain)** Linux:--- usual build chain (g++, etc)
Release pages:** JDK 10--- http://openjdk.java.net/projects/jdk/10/** JDK 11--- http://openjdk.java.net/projects/jdk/11/
Building OpenJDK project** Clone root repo:--- hg clone http://hg.openjdk.java.net/jdk/jdk** Go get JDK 10, use branch name (described in release page)** Note that all future JDK releases will use timestamped version name--- 18.3 (March 2018) or 18.9 (Sept 2018)
Source layout** one large project, made up of modules--- did away with "subprojects"** each module is made up of Java and native source
Source layout** demo, sample** solaris, bsd, linux** hotspot, utils** java.base, java.compiler, java.se, ...
Source layout** each module broken into parts*** share*** os (linux, windows, bsd, etc)*** nashorn** within that, further breakdown*** classes: Java code*** native: C/C++ code*** conf: configuration files (usually just copied)*** lib: external libraries*** legal: legal disclaimers/messages/licenses*** doc: man-page documentation
Configure the makefiles** run the "configure" script to configure all the makefiles--- bash configure** note that any missing dependencies will be flagged and configure will terminate** check out ./README-builds.html for build details
Requirements** All:*** a "boot JDK" installation for Java files compilation*** generally the boot JDK must be one version behind (JDK 7)** MacOS:--- XCode 9 and command-line tools** Windows:*** Visual Studio 2017*** Cygwin (for Unix-style build chain)** Linux:--- usual build chain (g++, etc)
Configure flags of note
** run "configure --help" for full list** three different kinds of builds:*** release*** optimized (release + some debug flags)*** fastdebug (debug w/some optimizations)*** slowdebug (debug w/o optimizations)
Find the java "launcher" code (java / java.exe)
Change the java.vendor system property
Get a list of all the -XX flags in a diagnostic build
Find where -XX:DisableExplicitGC is checked
Write your own garbage collector
Write your own garbage collector** make sure to handle any size heap from 8m to 1024GB
Write your own garbage collector** make sure to handle any size heap from 8m to 1024GB** make sure to do any GC pass on O(1) time
Who is this guy?
Architect, Engineering Manager/Leader, "force multiplier"
Co-founder, Solidify US
http://www.solidify.dev
Principal -- Neward & Associates
Author
Professional F# 2.0 (w/Erickson, et al; Wrox, 2010)
Effective Enterprise Java (Addison-Wesley, 2004)
SSCLI Essentials (w/Stutz, et al; OReilly, 2003)
Server-Based Java Programming (Manning, 2000)
See http://www.newardassociates.com