Oracle Corporation OSCON 2012

Transcription

1 Oracle Corporation OSCON 2012

2 Reducing Technical Debt in OpenJDK The Legacy and the Burden Stuart W. Marks Oracle JDK Core Libraries Group Oracle Corporation OSCON 2012

3 Let s Look At Some Code /* * Given several Strings, return the Strings * whose lengths are even. */ Vector evenlengths(vector strings) { Vector result = new Vector(); for (Enumeration e = strings.elements(); e.hasmoreelements(); ) { String s = (String)e.nextElement(); if (s.length() & 1 == 0) result.addelement(s); } return result; } Oracle Corporation OSCON 2012

4 Rewrite Using Modern Java /* * Given several Strings, return the Strings * whose lengths are even. */ List<String> evenlengths(list<string> strings) { List<String> result = new ArrayList<>(); for (String s : strings) { if (s.length() & 1 == 0) result.add(s); } return result; } Oracle Corporation OSCON 2012

5 Technical Debt Something you did (or failed to do) in the past that imposes present and future costs Increased difficulty of bugfixes/enhancements Reduced quality, greater risks of making changes Costs are like paying interest on a debt Canonical example: Take a shortcut now in order to ship sooner Clean up or fix it after release Typical example: Little messes build up inexorably Oracle Corporation OSCON 2012

6 Signs and Symptoms of Technical Debt duplicated code quick-n-dirty TODO messy makefiles balky build system unreliable tests we don t have time to do it right obsolescent code answering a question raises two new ones FIXME we ll clean it up later big bug backlog this is loathsome XXX Oracle Corporation OSCON 2012

7 Is Obsolescent Code Really Technical Debt? Yes, it really does slow us down. Was Vector used intentionally instead of ArrayList? for example, for thread safety or was the code written before ArrayList existed? Old APIs are unfamiliar, verbose, noisy Use of raw types provides less information (content type of a collection) calls into question the downcast s safety covers up atrocities (type-unsafe heterogenous collections) Oracle Corporation OSCON 2012

8 Is It Worth Modernizing the Code? No, it s not worth it. If it ain t broke, don t fix it Code behaves correctly as written Not causing test failures Not causing defects reported by customers Changes risk breaking something Opportunity cost (vs features, fixing actual bugs) Oracle Corporation OSCON 2012

9 Is It Worth Modernizing the Code? Yes, maintainability is often neglected. Bugfixing and feature work generally makes code less maintainable At some point enough debt may accumulate that feature work and bugfixing grinds to a halt Modernizing code prepares for future evolution OpenJDK ought to be a good example of Java programming Theoretically, cleanup should occur as work is done In practice, Oracle Corporation OSCON 2012

10 Is It Worth Modernizing the Code? Yes. Code modernization has provided actual benefits Coinification provided language feedback in JDK 7 Improved code quality & maintainability Found & fixed actual bugs, including a security vulnerability Potential for better results from static analysis tools Risks are low Choose safe cleanup work Warnings cleanup introduced a couple very minor bugs Follow usual review and testing procedures Oracle Corporation OSCON 2012

11 OpenJDK Modernization, Recent History JDK7: Coinification Update JDK code to use JDK 7 Project Coin features diamond multi-catch with precise rethrow try-with-resources Not comprehensive, mainly proof-of-concept Latent bugs found & fixed by try-with-resources refactoring JDK8: Java Warnings Cleanup (in progress) Oracle Corporation OSCON 2012

12 Warnings History Java 5 (2004) added generics Java previously had no warnings Unchecked/unsafe operations generated mandatory warnings Note: Warning.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details. Intended as code migration aid Most Java APIs updated to use generics JDK implementation to be updated later Java 7 (2011) javac greatly expanded lint warnings Oracle Corporation OSCON 2012

13 Warnings Example public class Warning { void m() { List list = new ArrayList(); list.add("duke"); } } $ javac Warning.java Note: Warning.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details. $ javac Xlint:all Warning.java Warning.java:6: warning: [unchecked] unchecked call to add(e) as a member of the raw type java.util.list list.add("duke"); ^ 1 warning Oracle Corporation OSCON 2012

14 Warnings Cleanup Summer Intern 2011 (Sasha Boulgakov) Analyzed and cleaned up warnings Initial javac warnings in jdk subrepo: 13,500 See next slide, breakdown by warnings type Additional Cleanup Efforts Warnings Cleanup Day, Dec 2011 London Java Community s Warnings Hack Days Current warnings count: 7, Oracle Corporation OSCON 2012

15 Warnings Breakdown by Type rawtypes) 6284) 46.3%) unchecked) 3389) 25.0%) depreca:o n) 1320) 9.7%) serial) 1067) 7.9%) cast) 757) 5.6%) sta:c) 502) 3.7%) fallthrough) 150) 1.1%) other) 104) 0.8%)!"#$%&'() *+,-',.'/) /'&!',"01+) ('!2"3),"($) ($"0,) 4"33$-!1*5-) 1$-'!) Oracle Corporation OSCON 2012

16 rawtypes + unchecked + deprecation = 81% Oracle Corporation OSCON 2012

17 The vast majority of OpenJDK s javac warning messages come not from actions that have added technical debt, but instead from inaction, where unchanging code is slowly obsoleted by surrounding changes in the platform Oracle Corporation OSCON 2012

18 The Legacy OpenJDK, like most projects, has technical debt It has its fair share Unpaid debt incurred intentionally Unpaid debt from messes, quick fixes, etc. OpenJDK has technical debt from platform evolution Language, library APIs, and compiler have evolved significantly Old, 1990s era code is obsolescent and has turned into debt Oracle Corporation OSCON 2012

19 The Burden Long-term maintainability of OpenJDK Need to keep modernizing the code base Invest in future maintenance and evolution Pay down technical debt (or at least keep it stable) OpenJDK is a going concern We can t default on our technical debt Oracle Corporation OSCON 2012

20 Future Work Continue modernization incrementally Warnings cleanup (mostly generics) Java 7 features: diamond, try-with-resources, switch over string Enhanced for-loop Vector, Hashtable, StringBuffer Broad collaboration within community on this effort But wait... what about Java 8 and Lambda? History doesn t repeat itself, but it rhymes Oracle Corporation OSCON 2012

21 Rewrite Using Modern Java /* * Given several Strings, return the Strings * whose lengths are even. */ List<String> evenlengths(list<string> strings) { List<String> result = new ArrayList<>(); for (String s : strings) { if (s.length() & 1 == 0) result.add(s); } return result; } Oracle Corporation OSCON 2012

22 Rewrite Using Postmodern Java (Lambda) /* * Given several Strings, return the Strings * whose lengths are even. */ List<String> evenlengths(list<string> strings) { return strings.filter(s -> s.length() & 1 == 0).into(new ArrayList<>()); } PRELIMINARY SUBJECT TO CHANGE Oracle Corporation OSCON 2012

23 References Technical Debt Martin Fowler: Steve McConnell: Getting Involved OpenJDK AdoptOpenJDK Oracle Corporation OSCON 2012

24 The preceding is intended to outline our general product direction. It is intended for information purposes only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code, or functionality, and should not be relied upon in making purchasing decisions. The development, release, and timing of any features or functionality described for Oracle s products remains at the sole discretion of Oracle Oracle Oracle Corporation OSCON 2012

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