JDK-8180325 : Use ClassLoaderData::classes_do for CDS classes
  • Type: Bug
  • Component: hotspot
  • Sub-Component: runtime
  • Affected Version: 10
  • Priority: P3
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2017-05-12
  • Updated: 2019-05-22
  • Resolved: 2017-05-17
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JDK 10
10 b21Fixed
Related Reports
Relates :  
JDK-8026985 - Rewrite SystemDictionary::classes_do and Dictionary::classes_do to use KlassClosure
Relates :  
JDK-7133093 - Improve system dictionary performance
Relates :  
JDK-8180310 - [testlibrary] TestSocketFactory null pointer when updating match bytes
Description
ClassDataSharing classes should be dumped using the ClassLoaderData::_classes list.  Currently the code uses SystemDictionary::dictionary() which also contains classes that are initiated by different loaders than owning loaders.   Practically this doesn't affect CDS, since only the boot loader is present, but it necessitates calling the SystemDictionary::classes_do() function that passed the ClassLoaderData because some loaders in the table are NULL for CDS.

The list of loaded classes is found on the ClassLoaderData and includes array classes, anonymous classes, redefined classes, and unloaded classes.  For CDS the closure filters these out.
Comments
From earlier call chasing of SystemDictionary::classes_do memory/metaspaceShared.cpp: SystemDictionary::classes_do(collect_classes2); which? This is a special case for a bug that calls the classes_do function with ClassLoaderData argument that returns the initiating loader because the system dictionary may have NULL ClassLoaderData (or so the comment says). So this creates a GrowableArray with duplicate class entries which are filtered out. This would be more correct to walk the CLDG loaded classes, and filter out array and anonymous classes tested by? CDS -Xshare:dump memory/metaspaceShared.cpp: SystemDictionary::classes_do(link_one_shared_class, THREAD); memory/metaspaceShared.cpp: SystemDictionary::classes_do(check_one_shared_class); which? loaded instanceKlasses but not anonymous classes. tested by? CDS -Xshare:dump
12-05-2017