1) Add check in ServerManagerTest to make sure that the Segment has been "checked out" before the factory ever sees it.

2) Some code readability changes to ReferenceCountingSegment

server/src/main/java/com/metamx/druid/index/ReferenceCountingSegment.java

@@ -46,11 +46,11 @@ public class ReferenceCountingSegment implements Segment
   public Segment getBaseSegment()
   {
     synchronized (lock) {
-      if (!isClosed) {
-        return baseSegment;
+      if (isClosed) {
+        return null;
       }
 
-      return null;
+      return baseSegment;
     }
   }
 
@@ -68,11 +68,11 @@ public class ReferenceCountingSegment implements Segment
   public String getIdentifier()
   {
     synchronized (lock) {
-      if (!isClosed) {
-        return baseSegment.getIdentifier();
+      if (isClosed) {
+        return null;
       }
 
-      return null;
+      return baseSegment.getIdentifier();
     }
   }
 
@@ -80,11 +80,11 @@ public class ReferenceCountingSegment implements Segment
   public Interval getDataInterval()
   {
     synchronized (lock) {
-      if (!isClosed) {
-        return baseSegment.getDataInterval();
+      if (isClosed) {
+        return null;
       }
 
-      return null;
+      return baseSegment.getDataInterval();
     }
   }
 
@@ -92,11 +92,11 @@ public class ReferenceCountingSegment implements Segment
   public QueryableIndex asQueryableIndex()
   {
     synchronized (lock) {
-      if (!isClosed) {
-        return baseSegment.asQueryableIndex();
+      if (isClosed) {
+        return null;
       }
 
-      return null;
+      return baseSegment.asQueryableIndex();
     }
   }
 
@@ -104,11 +104,11 @@ public class ReferenceCountingSegment implements Segment
   public StorageAdapter asStorageAdapter()
   {
     synchronized (lock) {
-      if (!isClosed) {
-        return baseSegment.asStorageAdapter();
+      if (isClosed) {
+        return null;
       }
 
-      return null;
+      return baseSegment.asStorageAdapter();
     }
   }
 
@@ -116,24 +116,18 @@ public class ReferenceCountingSegment implements Segment
   public void close() throws IOException
   {
     synchronized (lock) {
-      log.info("Trying to close %s", baseSegment.getIdentifier());
-      if (!isClosed) {
-        if (numReferences > 0) {
-          log.info(
-              "%d references to %s still exist. Decrementing instead.",
-              numReferences,
-              baseSegment.getIdentifier()
-          );
-
-          decrement();
-        } else {
-          log.info("Closing %s, numReferences: %d", baseSegment.getIdentifier(), numReferences);
-
-          baseSegment.close();
-          isClosed = true;
-        }
-      } else {
+      if (isClosed) {
         log.info("Failed to close, %s is closed already", baseSegment.getIdentifier());
+        return;
+      }
+
+      if (numReferences > 0) {
+        log.info("%d references to %s still exist. Decrementing.", numReferences, baseSegment.getIdentifier());
+
+        decrement();
+      } else {
+        log.info("Closing %s", baseSegment.getIdentifier());
+        innerClose();
       }
     }
   }
@@ -141,38 +135,50 @@ public class ReferenceCountingSegment implements Segment
   public Closeable increment()
   {
     synchronized (lock) {
-      if (!isClosed) {
-        numReferences++;
-        final AtomicBoolean decrementOnce = new AtomicBoolean(false);
-        return new Closeable()
-        {
-          @Override
-          public void close() throws IOException
-          {
-            if (decrementOnce.compareAndSet(false, true)) {
-              decrement();
-            }
-          }
-        };
+      if (isClosed) {
+        return null;
       }
 
-      return null;
+      numReferences++;
+      final AtomicBoolean decrementOnce = new AtomicBoolean(false);
+      return new Closeable()
+      {
+        @Override
+        public void close() throws IOException
+        {
+          if (decrementOnce.compareAndSet(false, true)) {
+            decrement();
+          }
+        }
+      };
     }
   }
 
   private void decrement()
   {
     synchronized (lock) {
-      if (!isClosed) {
-        if (--numReferences < 0) {
-          try {
-            close();
-          }
-          catch (Exception e) {
-            log.error("Unable to close queryable index %s", getIdentifier());
-          }
+      if (isClosed) {
+        return;
+      }
+
+      if (--numReferences < 0) {
+        try {
+          innerClose();
+        }
+        catch (Exception e) {
+          log.error("Unable to close queryable index %s", getIdentifier());
         }
       }
     }
   }
+
+  private void innerClose() throws IOException
+  {
+    synchronized (lock) {
+      log.info("Closing %s, numReferences: %d", baseSegment.getIdentifier(), numReferences);
+
+      isClosed = true;
+      baseSegment.close();
+    }
+  }
 }

server/src/main/java/com/metamx/druid/query/ReferenceCountingSegmentQueryRunner.java

@@ -12,7 +12,7 @@ import java.io.Closeable;
 */
 public class ReferenceCountingSegmentQueryRunner<T> implements QueryRunner<T>
 {
-  private final QueryRunner<T> runner;
+  private final QueryRunnerFactory<T, Query<T>> factory;
   private final ReferenceCountingSegment adapter;
 
   public ReferenceCountingSegmentQueryRunner(
@@ -20,9 +20,8 @@ public class ReferenceCountingSegmentQueryRunner<T> implements QueryRunner<T>
       ReferenceCountingSegment adapter
   )
   {
+    this.factory = factory;
     this.adapter = adapter;
-
-    this.runner = factory.createRunner(adapter);
   }
 
   @Override
@@ -30,7 +29,7 @@ public class ReferenceCountingSegmentQueryRunner<T> implements QueryRunner<T>
   {
     final Closeable closeable = adapter.increment();
     try {
-      final Sequence<T> baseSequence = runner.run(query);
+      final Sequence<T> baseSequence = factory.createRunner(adapter).run(query);
 
       return new ResourceClosingSequence<T>(baseSequence, closeable);
     }

server/src/test/java/com/metamx/druid/coordination/ServerManagerTest.java

@@ -73,6 +73,7 @@ import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
 
 /**
  */
@@ -262,7 +263,7 @@ public class ServerManagerTest
         )
     );
 
-    queryNotifyLatch.await();
+    queryNotifyLatch.await(25, TimeUnit.MILLISECONDS);
 
     Assert.assertEquals(1, factory.getSegmentReferences().size());
 
@@ -301,7 +302,7 @@ public class ServerManagerTest
         )
     );
 
-    queryNotifyLatch.await();
+    queryNotifyLatch.await(25, TimeUnit.MILLISECONDS);
 
     Assert.assertEquals(1, factory.getSegmentReferences().size());
 
@@ -344,7 +345,7 @@ public class ServerManagerTest
         )
     );
 
-    queryNotifyLatch.await();
+    queryNotifyLatch.await(25, TimeUnit.MILLISECONDS);
 
     Assert.assertEquals(1, factory.getSegmentReferences().size());
 
@@ -378,7 +379,7 @@ public class ServerManagerTest
   private void waitForTestVerificationAndCleanup(Future future)
   {
     try {
-      queryNotifyLatch.await();
+      queryNotifyLatch.await(25, TimeUnit.MILLISECONDS);
       queryWaitYieldLatch.countDown();
       queryWaitLatch.countDown();
       future.get();
@@ -505,13 +506,13 @@ public class ServerManagerTest
       if (!(adapter instanceof ReferenceCountingSegment)) {
         throw new IAE("Expected instance of ReferenceCountingSegment, got %s", adapter.getClass());
       }
-      segmentReferences.add((ReferenceCountingSegment) adapter);
-      adapters.add((SegmentForTesting) ((ReferenceCountingSegment) adapter).getBaseSegment());
+      final ReferenceCountingSegment segment = (ReferenceCountingSegment) adapter;
+
+      Assert.assertTrue(segment.getNumReferences() > 0);
+      segmentReferences.add(segment);
+      adapters.add((SegmentForTesting) segment.getBaseSegment());
       return new BlockingQueryRunner<Result<SearchResultValue>>(
-          new NoopQueryRunner<Result<SearchResultValue>>(),
-          waitLatch,
-          waitYieldLatch,
-          notifyLatch
+          new NoopQueryRunner<Result<SearchResultValue>>(), waitLatch, waitYieldLatch, notifyLatch
       );
     }
 
@@ -702,7 +703,7 @@ public class ServerManagerTest
       notifyLatch.countDown();
 
       try {
-        waitYieldLatch.await();
+        waitYieldLatch.await(25, TimeUnit.MILLISECONDS);
       }
       catch (Exception e) {
         throw Throwables.propagate(e);
@@ -715,7 +716,7 @@ public class ServerManagerTest
         public OutType get()
         {
           try {
-            waitLatch.await();
+            waitLatch.await(25, TimeUnit.MILLISECONDS);
           }
           catch (Exception e) {
             throw Throwables.propagate(e);