[GitHub] [helix] narendly commented on a change in pull request #788: Implement request forwarding for ZkRoutingDataWriter

[GitBox <gi...@apache.org>]

narendly commented on a change in pull request #788: Implement request forwarding for ZkRoutingDataWriter
URL: https://github.com/apache/helix/pull/788#discussion_r384310461
 
 

 ##########
 File path: helix-rest/src/main/java/org/apache/helix/rest/metadatastore/ZkMetadataStoreDirectory.java
 ##########
 @@ -42,49 +42,77 @@
 
 
 /**
+ * NOTE: This is a singleton class. DO NOT EXTEND!
  * ZK-based MetadataStoreDirectory that listens on the routing data in routing ZKs with a update
  * callback.
  */
 public class ZkMetadataStoreDirectory implements MetadataStoreDirectory, RoutingDataListener {
   private static final Logger LOG = LoggerFactory.getLogger(ZkMetadataStoreDirectory.class);
 
-  // TODO: enable the line below when implementation is complete
   // The following maps' keys represent the namespace
-  private final Map<String, MetadataStoreRoutingDataReader> _routingDataReaderMap;
-  private final Map<String, MetadataStoreRoutingDataWriter> _routingDataWriterMap;
-  private final Map<String, MetadataStoreRoutingData> _routingDataMap;
-  private final Map<String, String> _routingZkAddressMap;
+  // NOTE: made protected for testing reasons. DO NOT MODIFY!
+  protected final Map<String, MetadataStoreRoutingDataReader> _routingDataReaderMap;
+  protected final Map<String, MetadataStoreRoutingDataWriter> _routingDataWriterMap;
+  protected final Map<String, MetadataStoreRoutingData> _routingDataMap;
+  protected final Map<String, String> _routingZkAddressMap;
   // <namespace, <realm, <list of sharding keys>> mappings
-  private final Map<String, Map<String, List<String>>> _realmToShardingKeysMap;
+  protected final Map<String, Map<String, List<String>>> _realmToShardingKeysMap;
 
-  /**
-   * Creates a ZkMetadataStoreDirectory based on the given routing ZK addresses.
-   * @param routingZkAddressMap (namespace, routing ZK connect string)
-   * @throws InvalidRoutingDataException
-   */
-  public ZkMetadataStoreDirectory(Map<String, String> routingZkAddressMap)
+  private static volatile ZkMetadataStoreDirectory _zkMetadataStoreDirectoryInstance;
+
+  public static ZkMetadataStoreDirectory getInstance() {
+    if (_zkMetadataStoreDirectoryInstance == null) {
+      synchronized (ZkMetadataStoreDirectory.class) {
+        if (_zkMetadataStoreDirectoryInstance == null) {
+          _zkMetadataStoreDirectoryInstance = new ZkMetadataStoreDirectory();
+        }
+      }
+    }
+
+    return _zkMetadataStoreDirectoryInstance;
+  }
+
+  public static ZkMetadataStoreDirectory getInstance(String namespace, String zkAddress)
       throws InvalidRoutingDataException {
-    if (routingZkAddressMap == null || routingZkAddressMap.isEmpty()) {
-      throw new InvalidRoutingDataException("Routing ZK Addresses given are invalid!");
+    if (_zkMetadataStoreDirectoryInstance == null) {
+      synchronized (ZkMetadataStoreDirectory.class) {
+        if (_zkMetadataStoreDirectoryInstance == null) {
+          _zkMetadataStoreDirectoryInstance = new ZkMetadataStoreDirectory();
+        }
+      }
     }
-    _routingDataReaderMap = new HashMap<>();
-    _routingDataWriterMap = new HashMap<>();
-    _routingZkAddressMap = routingZkAddressMap;
+    _zkMetadataStoreDirectoryInstance.init(namespace, zkAddress);
 
 Review comment:
   Can you do
   
   getInstance().init(namespace, zkAddress) here to cut down on duplicate code?

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