RFR: 8261154: Memory leak in Java_java_lang_ClassLoader_defineClass0 with long class names

[Claes Redestad]

On Thu, 4 Feb 2021 15:48:16 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> This patch resolves a potential memory leak in Java_java_lang_ClassLoader_defineClass0
>> 
>> I've not figured a good way to write a regression test. A crude way to manually verify the leak and the fix is provided by the added microbenchmark that triggers the malloc in ClassLoader.c and the associated leak.
>> 
>> E.g., running this with `/usr/bin/time -v $BUILD_DIR/images/jdk/bin/java -Xmx256m -jar $BUILD_DIR/images/test/micro/benchmarks.jar LookupDef.*WeakClass.loadLong -f 0 -i  N | grep "Maximum resident set"` yields:
>> 
>> Baseline:
>> N = 20     Maximum resident set size (kbytes): 544860
>> N = 50     Maximum resident set size (kbytes): 818532
>> N = 100    Maximum resident set size (kbytes): 1388560
>> Patch:
>> N = 20     Maximum resident set size (kbytes): 480476
>> N = 50     Maximum resident set size (kbytes): 764040
>> N = 100    Maximum resident set size (kbytes): 782920
>
> Hi Cleas,
> 
> looks good but why changing the the NULL comparisons? 
> 
> If you wanted to simplify you could completely omit the NULL checks since free(NULL) is a noop. And potentially merge the labels - where there are two - into one.
> 
> Cheers, Thomas

I'm not sure every platform have always agreed free(NULL) is a noop. I suspect all the currently supported ones do, though?

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PR: https://git.openjdk.java.net/jdk/pull/2407