JDK-8164512 : Replace ClassLoader use of finalizer with phantom reference to unload native library
  • Type: Enhancement
  • Component: core-libs
  • Sub-Component: java.lang:class_loading
  • Affected Version: 10
  • Priority: P3
  • Status: Resolved
  • Resolution: Fixed
  • Submitted: 2016-08-19
  • Updated: 2018-03-23
  • Resolved: 2017-11-07
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JDK 10
10 b31Fixed
Related Reports
Blocks :  
JDK-8188052 - JNI FindClass needs to specify the class loading context used for library lifecycle hooks
CSR :  
JDK-8187882 - Replace ClassLoader use of finalizer with phantom reference to unload native library
Duplicate :  
JDK-6219879 - (cl) ClassLoader.NativeLibrary.load should be consistent in initialization of handleID
Relates :  
JDK-5086661 - JDK 1.5's temporary native libraries may not be deleted on VM exit
Relates :  
JDK-8253568 - Replace and mitigate Object.finalize() uses in JDK libraries
Relates :  
JDK-8191360 - Lookup of critical JNI method causes duplicate library loading with leaking handler
Description
This issue will track the work to convert ClassLoader finalizer to use phantom reference to unload native library.

An earlier prototype uncovers an issue related to JNI_FindClass that is called during JNI_OnUnload that resurrects the caller class which has been GC'ed.

I think JNI FindClass should not be called during JNI_OnUnload [1].   This would require further investigation, for example, whether it's possible to prohibit JNI_FindClass is called during JNI_OnUnload (to avoid resurrecting the caller's class).  Also might be useful to gather some data to determine how high the compatibility risk is for JNI_FindClass not to work in JNI_OnUnload. 

1] https://bugs.openjdk.java.net/browse/JDK-4240589?focusedCommentId=13474512&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-13474512