Uploaded image for project: 'Lucene - Core'
  1. Lucene - Core
  2. LUCENE-5887

Remove horrible WeakIdentityMap caching in AttributeFactory, AttributeSource and VirtualMethod

Attach filesAttach ScreenshotVotersWatch issueWatchersCreate sub-taskLinkCloneUpdate Comment AuthorReplace String in CommentUpdate Comment VisibilityDelete Comments
    XMLWordPrintableJSON

Details

    • Improvement
    • Status: Resolved
    • Major
    • Resolution: Fixed
    • None
    • 4.10, 6.0
    • None
    • None
    • New

    Description

      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...

      Attachments

        Activity

          This comment will be Viewable by All Users Viewable by All Users
          Cancel

          People

            uschindler Uwe Schindler
            uschindler Uwe Schindler
            Votes:
            0 Vote for this issue
            Watchers:
            1 Start watching this issue

            Dates

              Created:
              Updated:
              Resolved:

              Slack

                Issue deployment