Github user ctubbsii commented on a diff in the pull request:
https://github.com/apache/accumulo/pull/292#discussion_r133070150
--- 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) {
+ Table.ID tableId;
+ synchronized (tableIds) {
+ WeakReference<Table.ID> tableIdRef = tableIds.get(tableIdString);
+ if (tableIdRef != null) {
+ tableId = tableIdRef.get();
+ if (tableId != null) {
+ return tableId;
+ }
+ }
+
+ tableId = new ID(tableIdString);
+ tableIds.put(tableIdString, new WeakReference<>(tableId));
--- End diff --
The main point is that these objects, even the extra String instances,
would only be created when needed. Usually, the previous instance would be
used. Still can't avoid the potential duplicates I mentioned earlier, unless
you force removal of the old value before calling `put` in the case where `ref
!= null && ref.get() == null`, but the new String instances should dramatically
decrease the liklihood of this happening, and a few dupes are probably okay.
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