HBASE-14361 ReplicationSink should create Connection instances lazily

hbase-server/src/main/java/org/apache/hadoop/hbase/replication/regionserver/ReplicationSink.java

@@ -72,9 +72,12 @@ public class ReplicationSink {
 
   private static final Log LOG = LogFactory.getLog(ReplicationSink.class);
   private final Configuration conf;
-  private final Connection sharedHtableCon;
+  // Volatile because of note in here -- look for double-checked locking:
+  // http://www.oracle.com/technetwork/articles/javase/bloch-effective-08-qa-140880.html
+  private volatile Connection sharedHtableCon;
   private final MetricsSink metrics;
   private final AtomicLong totalReplicatedEdits = new AtomicLong();
+  private final Object sharedHtableConLock = new Object();
 
   /**
    * Create a sink for replication
@@ -88,7 +91,6 @@ public class ReplicationSink {
     this.conf = HBaseConfiguration.create(conf);
     decorateConf();
     this.metrics = new MetricsSink();
-    this.sharedHtableCon = ConnectionFactory.createConnection(this.conf);
   }
 
   /**
@@ -213,7 +215,14 @@ public class ReplicationSink {
    */
   public void stopReplicationSinkServices() {
     try {
+      if (this.sharedHtableCon != null) {
+        synchronized (sharedHtableConLock) {
+          if (this.sharedHtableCon != null) {
             this.sharedHtableCon.close();
+            this.sharedHtableCon = null;
+          }
+        }
+      }
     } catch (IOException e) {
       LOG.warn("IOException while closing the connection", e); // ignoring as we are closing.
     }
@@ -232,7 +241,17 @@ public class ReplicationSink {
     }
     Table table = null;
     try {
-      table = this.sharedHtableCon.getTable(tableName);
+      // See https://en.wikipedia.org/wiki/Double-checked_locking
+      Connection connection = this.sharedHtableCon;
+      if (connection == null) {
+        synchronized (sharedHtableConLock) {
+          connection = this.sharedHtableCon;
+          if (connection == null) {
+            connection = this.sharedHtableCon = ConnectionFactory.createConnection(this.conf);
+          }
+        }
+      }
+      table = connection.getTable(tableName);
       for (List<Row> rows : allRows) {
         table.batch(rows, null);
       }