Questions about JDK-8136353 "ClassValue preventing class unloading"

[Rob McKenna]

I think this is better suited for compiler-dev.

	-Rob

On 06/01/16 14:56, Craig Andrews wrote:
> I apologize for contacting this list - I'm sure this isn't the "right
> way" to contact the OpenJDK project, but I'm not clear what the "right
> way" is.
>
> I'm hoping to raise https://bugs.openjdk.java.net/browse/JDK-8136353
> "ClassValue preventing class unloading" as I believe it's a significant
> issue in ClassValue which is a blocker for its use in dynamic languages
> (which is primiarly why ClassValue was introduced). I think the P5
> priority set on the bug now is way too low, perhaps you could consider
> raising the priority?
>
> The source code in the issue description is incorrect; it doesn't
> compile. Could you please attach the working test cases to the issue, so
> future testers and developers can reproduce the problem? Here are links
> to the 2 source code files:
> https://issues.apache.org/jira/secure/attachment/12765900/CVTest.java
> https://issues.apache.org/jira/secure/attachment/12765901/MyClassValue.java
> (which of course should be directly attached to the openjdk issue
> tracker issue, and not hyperlinked to the Groovy tracker)
>
> And to reproduce the issue, run:
> $ javac MyClassValue.java && javac CVTest.java && mkdir -p t && jar cvf
> t/t.jar MyClassValue*.class && rm MyClassValue*.class &&
> JAVA_OPTS=-Xmx4m java CVTest
> and wait for the an error to occur, which is:
> Exception in thread "main" java.lang.OutOfMemoryError: Compressed class
> space
>      at java.lang.ClassLoader.defineClass1(Native Method)
>      at java.lang.ClassLoader.defineClass(ClassLoader.java:759)
>      at
> java.security.SecureClassLoader.defineClass(SecureClassLoader.java:152)
>      at java.net.URLClassLoader.defineClass(URLClassLoader.java:470)
>      at java.net.URLClassLoader.access$100(URLClassLoader.java:76)
>      at java.net.URLClassLoader$1.run(URLClassLoader.java:371)
>      at java.net.URLClassLoader$1.run(URLClassLoader.java:365)
>      at java.security.AccessController.doPrivileged(Native Method)
>      at java.net.URLClassLoader.findClass(URLClassLoader.java:364)
>      at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
>      at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
>      at CVTest.main(CVTest.java:12)
>
> The bug is reproducible on all JDK 8 and 9 builds (I tested up to JDK 9
> build 99).
>
> Based on my understanding of the situation from my research in the
> Groovy bug that discovered the issue (
> https://issues.apache.org/jira/browse/GROOVY-6704 ) and some work
> another person did with the YourKit profiler (
> https://www.yourkit.com/forum/viewtopic.php?f=3&t=12658 ), I suspect
> that the fix for https://bugs.openjdk.java.net/browse/JDK-8032606
> "ClassValue.ClassValueMap.type is unused" is relevant; I think the
> problem lies in the java.lang.Class.classValueMap implementation.
>
> Thank you,
> ~Craig Andrews