A Look at Software Library Usage in Java. Jürgen Starek 2012

Transcription

1 A Look at Software Library Usage in Java Jürgen Starek 2012

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3 Could it be that half of all that code is actually never used?

4 Could it be that half of all that code is actually never used? Who needs all that stuff, anyway?

5 Measuring API Usage 5 / 56

6 Outline 1. Terminology and Concepts 2. Instrumenting javac 3. Methods and Tools 4. Measurements 5. Insights 6 / 56

7 1. Terminology and Concepts 7 / 56

8 Terminology A software library is a set of routines that are packaged so that they can easily be included in other software. In the Java world: JAR-files 8 / 56

9 Terminology A software library exposes its internal code through a well-defined API. 9 / 56

10 Terminology APIs cover problem domains. A domain in this sense is an area of related tasks. Domains are intended to represent the main usage areas of an API. 10 / 56

11 Terminology A feature is either a field a method a constructor A feature reference is any programmatic access to a feature. 11 / 56

12 Terminology A corpus is a set of code that provides the base data for statistical analyses. 12 / 56

13 Motivation Why Measure API Usage? Little previous work Potential applications for library developers Starting point for further projects in our working group 13 / 56

14 Motivation Why Use Large Corpora? Test for selection biases in previous studies using smaller corpora Large quality differences in real-world software cover amateur programmers' usage Analyze what average programmers do Rare phenomena stand out less 14 / 56

15 2. Instrumenting javac 15 / 56

16 Instrumenting javac: The Problem We need complete information about each feature call With inheritance hierarchy, in order to catch interfaces 16 / 56

17 17 / 56

18 package org.cogkit.gridface.interfaces; import import import import java.util.calendar; java.util.enumeration; java.util.vector; java.util.hashtable; import org.cogkit.abstraction.interfaces.executableobject; import org.cogkit.abstraction.interfaces.statuslistener; import org.cogkit.abstraction.interfaces.task; /** * Grid command can be executed in cog-abstraction as tasks. */ public interface GridCommand extends StatusListener, ExecutableObject { public Task gettask(); public void settask(task newtask); public Integer getid(); public void setcommand(string command); public Vector getarguments(); public Calendar getsubmittedtime(); public Calendar getcompletedtime(); shortened example code from the CogKit project 18 / 56

19 package org.cogkit.gridface.interfaces; import import import import java.util.calendar; java.util.enumeration; java.util.vector; java.util.hashtable; import org.cogkit.abstraction.interfaces.executableobject; import org.cogkit.abstraction.interfaces.statuslistener; import org.cogkit.abstraction.interfaces.task; /** * Grid command can be executed in cog-abstraction as tasks. */ public interface GridCommand extends StatusListener, ExecutableObject { public Task gettask(); public void settask(task newtask); public Integer getid(); public void setcommand(string command); public Vector getarguments(); public Calendar getsubmittedtime(); public Calendar getcompletedtime(); shortened example code from the CogKit project 19 / 56

20 package org.cogkit.gridface.interfaces; import import import import java.util.calendar; java.util.enumeration; java.util.vector; java.util.hashtable; import org.cogkit.abstraction.interfaces.executableobject; import org.cogkit.abstraction.interfaces.statuslistener; import org.cogkit.abstraction.interfaces.task; /** * Grid command can be executed in cog-abstraction as tasks. */ public interface GridCommand extends StatusListener, ExecutableObject { public Task gettask(); public void settask(task newtask); public Integer getid(); public void setcommand(string command); public Vector getarguments(); public Calendar getsubmittedtime(); public Calendar getcompletedtime(); shortened example code from the CogKit project 20 / 56

21 package org.cogkit.gridface.interfaces; import import import import java.util.calendar; java.util.enumeration; java.util.vector; java.util.hashtable; import org.cogkit.abstraction.interfaces.executableobject; import org.cogkit.abstraction.interfaces.statuslistener; import org.cogkit.abstraction.interfaces.task; /** * Grid command can be executed in cog-abstraction as tasks. */ public interface GridCommand extends StatusListener, ExecutableObject { public Task gettask(); public void settask(task newtask); public Integer getid(); public void setcommand(string command); public Vector getarguments(); public Calendar getsubmittedtime(); public Calendar getcompletedtime(); shortened example code from the CogKit project 21 / 56

22 Counting occurences of add...? %> grep -ir \.add\( * grep -v.svn head examples/gcm/gcmdependencytest.java: examples/mimehandler/mimehandlereditortest.java: impl/commands/copycommandimpl.java: impl/commands/copycommandimpl.java: impl/commands/copydircommandimpl.java: impl/commands/copydircommandimpl.java: impl/commands/gridcommandimpl.java: impl/commands/gridcommandimpl.java: impl/commands/gridcommandimpl.java: impl/commands/copyfilecommandimpl.java: identities.add(0,previd); myframe.getcontentpane().add(mhe); taskgraph.add(gettask); taskgraph.add(puttask); taskgraph.add(gettask); taskgraph.add(puttask); this.arguments.add(args[i]); this.arguments.add(arg); statuslisteners.add(listener); taskgraph.add(gettask);...no. We need type information. 22 / 56

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25 Hacking into the compile chain javac compile stages Parse Enter Annotate Attribute Flow Desugar Generate From David Erni, Adrian Kuhn: The Hacker's Guide to Javac, Universität Bern, / 56

26 Hacking into the compile chain Injecting own code Custom annotation processor for all code Parse Enter Annotate JSR269 Attribute Flow Desugar Generate From David Erni, Adrian Kuhn: The Hacker's Guide to Javac, Universität Bern, / 56

27 Accessing public class Analyzer extends AbstractProcessor { // Initialize the public synchronized void init(processingenvironment procenv) { super.init(procenv); // Inject our TaskListener into the compiler context t = new TaskListen(); ((JavacProcessingEnvironment)procEnv).getContext().put(taskListener.class, t); } /** * Since we do our analysis elsewhere, returning false enables * other annotation processors to again process the same * annotations we encounter here, i.e. we don t claim them. public boolean process(set<? extends TypeElement> annotations, RoundEnvironment r) { return false; } 27 / 56

28 Automatically launching plugins ANT autoloads all JARs in ~/.ant/lib/ with correct service entry file 28 / 56

29 3. Methods and Tools 29 / 56

30 Source Corpus Creation Desired corpus properties: large many domains different code quality SourceForge as repository of choice Subversion & ANT only 30 / 56

31 The Analysis Process Search criteria SourceForge Repositories SVN Checkout Local source code repo Building and Fact extraction Relational database Manual API tagging Report usage data drives API selection Manual API selection Manual download Local binary API repo 31 / 56

32 API Corpus Creation Controlled, well-known set of APIs Core Java + 3rd party Initially: Manual download Later: Iterative extension of corpus Goal: > 50% of API features from known sources Manual tagging 32 / 56

33 The Analysis Process Search criteria SourceForge Repositories SVN Checkout Local source code repo Building and Fact extraction Relational database Manual API tagging Report usage data drives API selection Manual API selection Manual download Local binary API repo 33 / 56

34 Fact Extraction Instrumented javac Provides Access to entire AST Detailed type and inheritance information for every feature reference 34 / 56

35 The Analysis Process Search criteria SourceForge Repositories SVN Checkout Local source code repo Building and Fact extraction Relational database Manual API tagging Report usage data drives API selection Manual API selection Manual download Local binary API repo 35 / 56

36 The Database All feature references Which feature? From which API? Referenced from which project? Additionally: API data Metadata 36 / 56

37 Storage and Interpretation of Extracted Data Relational database MySQL MyISAM ~ 1.5 GB total Standard SQL queries Postprocessing and automation with Python Graphs with gnuplot 37 / 56

38 The Analysis Process Search criteria SourceForge Repositories SVN Checkout Local source code repo Building and Fact extraction Relational database Manual API tagging Report usage data drives API selection Manual API selection Manual download Local binary API repo 38 / 56

39 The Analysis Process Search criteria SourceForge Repositories SVN Checkout Local source code repo Building and Fact extraction Relational database Manual API tagging Report usage data drives API selection Manual API selection Manual download Local binary API repo Automated using makefiles 39 / 56

40 4. Measurements 40 / 56

41 Basic Corpus Data from AST-based Analyses Metric Built projects Packages Classes Methods Feature References Value / 56

42 Feature Sources in largest projects 42 / 56

43 Feature Sources Source All Projects Reference Projects Core Java Manually tagged APIs Automatically tagged APIs 32.2 % 9.9 % 8.6 % 41.2 % 27.8 % 21.5 % Default package Others 2.5 % 46.8 % 1.7 % 7.8 % 43 / 56

44 A detailed look at Feature Sources 44 / 56

45 Distinct APIs per project 45 / 56

46 API Feature Ratio 46 / 56

47 Feature Usage Distribution 47 / 56

48 Feature Usage Distribution of selected APIs from the XML Domain 48 / 56

49 Copying library code Lots of projects copy libraries' code into their own code repo Don't! Bloat Old versions Tracking of security issues 49 / 56

50 Copyright (C) 1998, 1999, 2001, 2004, 2005 Free Sof Free Software Foundation, Inc., 51 Franklin Street, Fif USA. package java.util; import java.io.ioexception; import java.io.objectinputstream; import java.io.objectoutputstream; import java.io.serializable; Jon Zeppieri Eric Blake (ebb9@ .byu.edu) TreeSet < Collections#synchronizedSet(Set) < LinkedHashSet < updated to 1.4 < public class HashSet<T> extends AbstractSet<T> implements Set<T>, Cloneable, Serializable private transient HashMap<T, String> map; public HashSet(int initialcapacity, float loadfactor) public HashSet(Collection<? extends T> c) public boolean add(t o) public Object clone() HashSet<T> copy = null; copy = (HashSet<T>) super.clone(); copy.map = (HashMap<T, String>) map.clone(); public Iterator<T> iterator() HashMap init(int capacity, float load) > Iterator<T> it = map.iterator(hashmap.keys); > map.put((t) s.readobject(), ""); > Copyright (C) 1998, 1999, 2001, 2004 Free Software Free Software Foundation, Inc., 59 Temple Place, USA. package org.placelab.collections; //import java.io.ioexception; //import java.io.objectinputstream; //import java.io.objectoutputstream; //import java.io.serializable; * * public class HashSet extends AbstractSet implements Set, Cloneable//, Serializable private transient HashMap map; public HashSet(int initialcapacity, int loadfactor) public HashSet(Collection c) public boolean add(object o) public Object pclone() HashSet copy = null; copy = (HashSet) super.pclone(); copy.map = (HashMap) map.pclone(); public Iterator iterator() HashMap init(int capacity, int load) /* NOT IN MIDP Iterator it = map.iterator(hashmap.keys); */ /* NOT IN MIDP map.put(s.readobject(), ""); */ sdiff output comparing two implementations of the HashSet class. - Left: API version as delivered with GNU Classpath Right: version from the tsg project Only lines that differ between the two versions are shown. 50 / 56

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52 5. Insights 52 / 56

53 Contributions A first glimpse at API usage in Open Source projects shallow and few New analysis method for automated corpus-based analyses Understanding of pitfalls and inaccuracies in automated analyses 53 / 56

54 Library best practices For library writers: Small, well-bounded problem domains Don't break compatibility For library users: Don't copy Use Decorator, Facade, Adapter patterns 54 / 56

55 Use cases for JSR269-based hacks immutablej: A javac annotation processor that makes Java variables default to immutable Code completion tools like Lombok / 56

56 Sources A Large-Scale Analysis of Java API Usage. Jürgen Starek. Diploma thesis, Universität Koblenz, 2012 The Hacker's Guide to Javac. David Erni, Adrian Kuhn. Universität Bern, 2008 Further reading Large-Scale, AST-based API-usage analysis of Open Source Java projects. Ralf Lämmel, Ekaterina Pek, Jürgen Starek. In: SAC '11 Proceedings of the 2011 ACM Symposium on Applied Computing, p ACM, New York, / 56