close transport client to wait for ongoing samples

the transport client should not be executing at the same time as sampling happens, so connection open/close logic will be properly maintained

src/main/java/org/elasticsearch/client/transport/TransportClientNodesService.java

@@ -23,6 +23,7 @@ import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Sets;
 import org.elasticsearch.ElasticSearchException;
+import org.elasticsearch.ElasticSearchIllegalStateException;
 import org.elasticsearch.ExceptionsHelper;
 import org.elasticsearch.Version;
 import org.elasticsearch.action.ActionListener;
@@ -69,7 +70,7 @@ public class TransportClientNodesService extends AbstractComponent {
     // nodes that are added to be discovered
     private volatile ImmutableList<DiscoveryNode> listedNodes = ImmutableList.of();
 
-    private final Object transportMutex = new Object();
+    private final Object mutex = new Object();
 
     private volatile ImmutableList<DiscoveryNode> nodes = ImmutableList.of();
 
@@ -129,7 +130,10 @@ public class TransportClientNodesService extends AbstractComponent {
     }
 
     public TransportClientNodesService addTransportAddresses(TransportAddress... transportAddresses) {
-        synchronized (transportMutex) {
+        synchronized (mutex) {
+            if (closed) {
+                throw new ElasticSearchIllegalStateException("transport client is closed, can't add an address");
+            }
             List<TransportAddress> filtered = Lists.newArrayListWithExpectedSize(transportAddresses.length);
             for (TransportAddress transportAddress : transportAddresses) {
                 boolean found = false;
@@ -155,13 +159,16 @@ public class TransportClientNodesService extends AbstractComponent {
                 builder.add(node);
             }
             listedNodes = builder.build();
+            nodesSampler.sample();
         }
-        nodesSampler.sample();
         return this;
     }
 
     public TransportClientNodesService removeTransportAddress(TransportAddress transportAddress) {
-        synchronized (transportMutex) {
+        synchronized (mutex) {
+            if (closed) {
+                throw new ElasticSearchIllegalStateException("transport client is closed, can't remove an address");
+            }
             ImmutableList.Builder<DiscoveryNode> builder = ImmutableList.builder();
             for (DiscoveryNode otherNode : listedNodes) {
                 if (!otherNode.address().equals(transportAddress)) {
@@ -171,8 +178,8 @@ public class TransportClientNodesService extends AbstractComponent {
                 }
             }
             listedNodes = builder.build();
+            nodesSampler.sample();
         }
-        nodesSampler.sample();
         return this;
     }
 
@@ -262,19 +269,33 @@ public class TransportClientNodesService extends AbstractComponent {
     }
 
     public void close() {
-        closed = true;
-        nodesSamplerFuture.cancel(true);
-        for (DiscoveryNode node : nodes) {
-            transportService.disconnectFromNode(node);
+        synchronized (mutex) {
+            if (closed) {
+                return;
+            }
+            closed = true;
+            nodesSamplerFuture.cancel(true);
+            for (DiscoveryNode node : nodes) {
+                transportService.disconnectFromNode(node);
+            }
+            for (DiscoveryNode listedNode : listedNodes) {
+                transportService.disconnectFromNode(listedNode);
+            }
+            nodes = ImmutableList.of();
         }
-        for (DiscoveryNode listedNode : listedNodes) {
-            transportService.disconnectFromNode(listedNode);
-        }
-        nodes = ImmutableList.of();
     }
 
-    interface NodeSampler {
-        void sample();
+    abstract class NodeSampler {
+        public void sample() {
+            synchronized (mutex) {
+                if (closed) {
+                    return;
+                }
+                doSample();
+            }
+        }
+
+        protected abstract void doSample();
     }
 
     class ScheduledNodeSampler implements Runnable {
@@ -291,13 +312,10 @@ public class TransportClientNodesService extends AbstractComponent {
         }
     }
 
-    class SimpleNodeSampler implements NodeSampler {
+    class SimpleNodeSampler extends NodeSampler {
 
         @Override
-        public synchronized void sample() {
-            if (closed) {
-                return;
-            }
+        protected void doSample() {
             HashSet<DiscoveryNode> newNodes = new HashSet<DiscoveryNode>();
             for (DiscoveryNode node : listedNodes) {
                 if (!transportService.nodeConnected(node)) {
@@ -332,14 +350,10 @@ public class TransportClientNodesService extends AbstractComponent {
         }
     }
 
-    class SniffNodesSampler implements NodeSampler {
+    class SniffNodesSampler extends NodeSampler {
 
         @Override
-        public synchronized void sample() {
-            if (closed) {
-                return;
-            }
-
+        protected void doSample() {
             // the nodes we are going to ping include the core listed nodes that were added
             // and the last round of discovered nodes
             Set<DiscoveryNode> nodesToPing = Sets.newHashSet();