add sync block

Author: sakthivelmanii

google-cloud-spanner/src/main/java/com/google/cloud/spanner/AsyncResultSetImpl.java

@@ -468,6 +468,11 @@ public void run() {
         // Those result sets will trigger initiateProduceRows() when the first results are received.
         // Non-streaming result sets do not trigger this callback, and for those result sets, we
         // need to eagerly start the ProduceRowsRunnable.
+        synchronized (monitor) {
+          if (!(state == State.STREAMING_INITIALIZED)) {
+            return;
+          }
+        }
         if (!initiateStreaming(AsyncResultSetImpl.this)) {
           initiateProduceRows();
         }
@@ -490,7 +495,6 @@ public ApiFuture<Void> setCallback(Executor exec, ReadyCallback cb) {
       this.result = SettableApiFuture.create();
       this.state = State.STREAMING_INITIALIZED;
       this.service.execute(new InitiateStreamingRunnable());
-//      initiateProduceRows();
       this.executor = MoreExecutors.newSequentialExecutor(Preconditions.checkNotNull(exec));
       this.callback = Preconditions.checkNotNull(cb);
       pausedLatch.countDown();