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https://issues.apache.org/jira/browse/LUCENE-5887?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Uwe Schindler updated LUCENE-5887:
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Attachment: LUCENE-5887.patch
New patch with some cleanups (renames of fields,...). Also made sure that the
collected interfaces for a given AttributeImpl dont have duplicae interfaces.
This was not guaranteed before, but was possible, if superclass defined same
interfaces as class. This happened with the Token class...
Will commit this now.
> Remove horrible WeakIdentityMap caching in AttributeFactory, AttributeSource
> and VirtualMethod
> ----------------------------------------------------------------------------------------------
>
> Key: LUCENE-5887
> URL: https://issues.apache.org/jira/browse/LUCENE-5887
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Uwe Schindler
> Assignee: Uwe Schindler
> Fix For: 5.0, 4.10
>
> Attachments: LUCENE-5887.patch, LUCENE-5887.patch
>
>
> Especially the use case in AttributeFactory is horrible:
> Because of ClassLoader issues we cannot hold strong references (see
> LUCENE-5640 for explanation), we need WeakIdentityMap<Class,
> WeakReference<someVal>>. You could say: let's use a strong value for stuff
> like MethodHandles (used in AttributeFactory), but because those have a
> strong reference to the class, our reference to key would be strong, so
> garbage collector can no longer unload the class. This is why we use the
> WeakReference also on the value.
> The problem is if the value is something like a MethodHandle, which itsself
> has hard reference to (so it gets garbage collected). Then the cache is
> useless.
> In DefaultAttributeFactory I decided, to make methodhandles strong
> references, but then I needed to restrict it to our own classloader,
> otherwise we would have strong references to foreign classloaders.
> Since Java 7 there is java.lang.ClassValue, that fixes the following JVM bug:
> http://bugs.java.com/bugdatabase/view_bug.do?bug_id=6389107
> See also: http://stackoverflow.com/questions/7444420/classvalue-in-java-7
> In fact internally, there is a also a WeakReference/WeakHashMap used, but
> only as fallback - and its only one globally, used by many other JVM
> internals, too. By default it has a very fast path and the call to
> ClassValue.get() is incredibly fast. This should therefore also improve
> AttributeFactory alltogether.
> Next to AttributeFactory, I also improved the Interfaces cache of
> AttributeSource (this one assigns an array of Attribute interfaces to an
> AttributeImpl). The other one is VirtualMethod (assigns its own
> implementationDistance for every seen subclass).
> This also removes almost all uses of WeakIdentityMap, the remaining one is
> the ByteBuffer stuff in MMapDirectory. Unfortunately I have still no idea how
> to remove that one... :(
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