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From milleruntime <...@git.apache.org>
Subject [GitHub] accumulo pull request #292: ACCUMULO-4681 Created Table & Namespace WeakRefe...
Date Mon, 14 Aug 2017 16:43:45 GMT
Github user milleruntime commented on a diff in the pull request:

    https://github.com/apache/accumulo/pull/292#discussion_r132999867
  
    --- 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<>();
     
    -    public static final ID METADATA = new ID("!0");
    -    public static final ID REPLICATION = new ID("+rep");
    -    public static final ID ROOT = new ID("+r");
    +    public static final ID METADATA = of("!0");
    +    public static final ID REPLICATION = of("+rep");
    +    public static final ID ROOT = of("+r");
     
    -    public ID(final String canonical) {
    +    private ID(final String canonical) {
           super(canonical);
         }
    +
    +    /**
    +     * Get a Table.ID object for the provided canonical string.
    +     *
    +     * @param canonical
    +     *          table ID string
    +     * @return Table.ID object
    +     */
    +    public static Table.ID of(final String canonical) {
    +      return dedupeTableId(canonical);
    +    }
    +
    +    private static Table.ID dedupeTableId(String tableIdString) {
    --- End diff --
    
    I thought about this but it would require reflection or passing a pre-constructed instance
object as a parameter to the method.  I wanted to avoid reflection since we lose some of the
type safety. I also wanted to avoid created objects every time for parameters since they may
not be needed if the map already contains the id.  
    
    Passing in a constructor object as a parameter may be a nice compromise but this introduces
a bunch of potential exceptions:
    <pre>
    try {
            id = constructor.newInstance(idString);
          } catch (InstantiationException e) {
            e.printStackTrace();
          } catch (IllegalAccessException e) {
            e.printStackTrace();
          } catch (InvocationTargetException e) {
            e.printStackTrace();
          }
          idHashMap.put(idString, new WeakReference<>(id));
    </pre>


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