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https://issues.apache.org/jira/browse/BCEL-317?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16879552#comment-16879552
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Gary Gregory commented on BCEL-317:
-----------------------------------
I've reworked the cache such that it can be enabled from system properties by
expanding the current use of system as documented in the class {{ConstantUtf8}}
class Javadoc:
The following system properties govern caching this class performs.
- "bcel.maxcached" (since 6.4): The size of the cache, by default 0, meaning
caching is disabled.
- "bcel.maxcached.size" (since 6.0): The maximum size of the values to cache,
by default 200, 0 disablescaching. Values larger than this are not cached.
- "bcel.statistics" (since 6.0): Prints statistics on the console when the JVM
exits.
Here is a sample Maven invocation with caching disabled:
{{mvn test -Dbcel.statistics=true -Dbcel.maxcached.size=0 -Dbcel.maxcached=0}}
Here is a sample Maven invocation with caching enabled:
{{mvn test -Dbcel.statistics=true -Dbcel.maxcached.size=100000
-Dbcel.maxcached=5000000}}
> Pluggable cache for ConstantUtf8
> --------------------------------
>
> Key: BCEL-317
> URL: https://issues.apache.org/jira/browse/BCEL-317
> Project: Commons BCEL
> Issue Type: Improvement
> Components: Main
> Affects Versions: 6.3.1
> Reporter: Tomo Suzuki
> Priority: Minor
> Attachments: 2644k_constantutf8_without_getCachedInstance.png,
> 621k_constantutf8_with_getCachedInstance.png
>
> Time Spent: 40m
> Remaining Estimate: 0h
>
> Follow-up of BCEL-186. This enhancement is to provide an option to cache
> ConstantUtf8 instances that have the same value.
>
> Email thread: [bcel] Idea to share ConstantUtf8 of same value among JavaClass
> instances
> --------------------
> We use BCEL library to inspect Java class. Thank you for the great library.
>
> When our tool checks classes in ~200 jar files, it creates more than 2
> million BCEL ConstantUtf8 instances. I suspect many of them share the same
> values such as "java.lang.String".
>
> Without cache, my tool created 2,6 million ConstantUtf8 instances (before
> failing OutOfMemoryError: GC overhead limit exceeded) to check ~200 jar files.
> !2644k_constantutf8_without_getCachedInstance.png!
>
> With the cache, my tool created just 0.6 million ConstantUtf8 instances. It
> didn't throw the OutOfMemoryError.
> !621k_constantutf8_with_getCachedInstance.png!
>
> Old commit that made ConstantUtf8.getInstance
> [https://svn.apache.org/viewvc/commons/proper/bcel/trunk/src/main/java/org/apache/bcel/classfile/Constant.java?r1=1481383&r2=1481382&pathrev=1481383]
> The ConstantUtf8.getInstance has been unused in BCEL since BCEL-186
> [http://svn.apache.org/viewvc/commons/proper/bcel/trunk/src/main/java/org/apache/bcel/classfile/ConstantUtf8.java?r1=1652541&r2=1652540&pathrev=1652541]
>
> h1. How our project uses BCEL
> - Our tool (Linkage Checker) creates BCEL's ClassPathRepository with around
> 200 JAR files as its input class path in
> ClassDumper.createClassRepository([source code
> URL|https://github.com/GoogleCloudPlatform/cloud-opensource-java/blob/239fb82e368b2c181e358359f758b33c0a122787/dependencies/src/main/java/com/google/cloud/tools/opensource/classpath/ClassDumper.java#L83])
> {code:java}
> private static Repository createClassRepository(List<Path> paths) {
> ClassPath classPath = new LinkageCheckClassPath(paths);
> return new ClassPathRepository(classPath); # This is BCEL API
> }{code}
> - reads JavaClasses one by one in ClassDumper.listClassesInJar ([source code
> URL|https://github.com/GoogleCloudPlatform/cloud-opensource-java/blob/239fb82e368b2c181e358359f758b33c0a122787/dependencies/src/main/java/com/google/cloud/tools/opensource/classpath/ClassDumper.java#L360])
> through the ClassPathRepository.
> {code:java}
> private ImmutableSet<JavaClass> listClassesInJar(Path jar) throws
> IOException {
> ImmutableSet.Builder<JavaClass> javaClasses = ImmutableSet.builder();
> for (String className : listClassNamesInJar(jar)) {
> try {
> JavaClass javaClass = classRepository.loadClass(className); # This is
> BCEL API. ConstantUtf8 is not cached.
> javaClasses.add(javaClass);
> ...(omit)
> return javaClasses.build();
> }{code}
> Stacktrace from the ClassDumper.listClassesInJar to BCEL's
> ConstantUtf8.getInstance would look like this:
> {code:java}
> ConstantUtf8.getInstance
> Constant.readConstant
> ConstantPool.<init>
> ClassParser.readConstantPool
> ClassParser.parse
> ClassPathRepository.loadClass
> ClassPathRepository.loadClass
> ClassDumper.listClassesInJar {code}
> - Use the JavaClass instances to check if any symbol references (entries in
> constant pool [Java Virtual Machine Specification 4.4. The Constant
> Pool|https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.4]:
> CONSTANT_Class, CONSTANT_Fieldref, CONSTANT_Methodref, and
> CONSTANT_InterfaceMethodref) has invalid referent in the class path.
>
>
>
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