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From ctubbsii <...@git.apache.org>
Subject [GitHub] accumulo pull request #292: ACCUMULO-4681 Created Table & Namespace WeakRefe...
Date Sat, 12 Aug 2017 19:34:40 GMT
Github user ctubbsii commented on a diff in the pull request:

    https://github.com/apache/accumulo/pull/292#discussion_r132823444
  
    --- Diff: core/src/main/java/org/apache/accumulo/core/client/impl/Table.java ---
    @@ -16,24 +16,59 @@
      */
     package org.apache.accumulo.core.client.impl;
     
    +import java.lang.ref.WeakReference;
    +import java.util.WeakHashMap;
    +
     import org.apache.accumulo.core.client.Instance;
     
     public class Table {
     
       /**
        * Object representing an internal table ID. This class was created to help with type
safety. For help obtaining the value of a table ID from Zookeeper, see
        * {@link Tables#getTableId(Instance, String)}
    +   *
    +   * Uses an internal WeakHashMap and private constructor for storing a WeakReference
of every Table.ID. Therefore, a Table.ID can't be instantiated outside
    +   * this class and is accessed by calling Table.ID.{@link #of(String)}.
        */
       public static class ID extends AbstractId {
         private static final long serialVersionUID = 7399913185860577809L;
    +    static final WeakHashMap<String,WeakReference<Table.ID>> tableIds = new
WeakHashMap<>();
    --- End diff --
    
    It occurs to me that because of Java string interning, using a String as a key may mean
that entries are kept around longer than necessary. The `WeakReference<Table.ID>` will
still remove unused `Table.ID` objects and it will dedupe when it does exist, but the map
entry might stick around unnecessarily because the String still has a strong reference because
it's used in more places than just the Table.ID. This could be avoided by always constructing
a new String and using that as the canonical parameter and the map key... but not sure it's
worth it.


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