Fix Router race condition and use default broker service name for invalid priority (#5050)

* use default brokerServiceName when priority is not valid

* use AtomicInteger for NodesHolder.roundRobinIndex

* revert inspectionProfiles change

* adjust TieredBrokerHostSelectorTest

* combine if statements and ensure index does not become negative

* set next index with mod if overflows

* fix codestyle

* use nextIndex

* extract the while loop to a method

server/src/main/java/io/druid/server/router/PriorityTieredBrokerSelectorStrategy.java

@@ -22,7 +22,6 @@ package io.druid.server.router;
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.google.common.base.Optional;
-import com.google.common.collect.Iterables;
 import io.druid.query.Query;
 import io.druid.query.QueryContexts;
 
@@ -48,19 +47,9 @@ public class PriorityTieredBrokerSelectorStrategy implements TieredBrokerSelecto
   {
     final int priority = QueryContexts.getPriority(query);
 
-    if (priority < minPriority) {
+    if (priority < minPriority || priority > maxPriority) {
       return Optional.of(
-          Iterables.getLast(
+          tierConfig.getDefaultBrokerServiceName()
-              tierConfig.getTierToBrokerMap().values(),
-              tierConfig.getDefaultBrokerServiceName()
-          )
-      );
-    } else if (priority >= maxPriority) {
-      return Optional.of(
-          Iterables.getFirst(
-              tierConfig.getTierToBrokerMap().values(),
-              tierConfig.getDefaultBrokerServiceName()
-          )
       );
     }
 

server/src/main/java/io/druid/server/router/TieredBrokerHostSelector.java

@@ -44,6 +44,7 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.atomic.AtomicInteger;
 
 /**
  */
@@ -277,7 +278,7 @@ public class TieredBrokerHostSelector<T>
 
   private static class NodesHolder
   {
-    private int roundRobinIndex = 0;
+    private AtomicInteger roundRobinIndex = new AtomicInteger(-1);
 
     private Map<String, Server> nodesMap = new HashMap<>();
     private ImmutableList<Server> nodes = ImmutableList.of();
@@ -312,11 +313,21 @@ public class TieredBrokerHostSelector<T>
         return null;
       }
 
-      if (roundRobinIndex >= currNodes.size()) {
+      return currNodes.get(getIndex(currNodes));
-        roundRobinIndex %= currNodes.size();
+    }
-      }
 
-      return currNodes.get(roundRobinIndex++);
+    int getIndex(ImmutableList<Server> currNodes)
+    {
+      while (true) {
+        int index = roundRobinIndex.get();
+        int nextIndex = index + 1;
+        if (nextIndex >= currNodes.size()) {
+          nextIndex = 0;
+        }
+        if (roundRobinIndex.compareAndSet(index, nextIndex)) {
+          return nextIndex;
+        }
+      }
     }
   }
 }

server/src/test/java/io/druid/server/router/TieredBrokerHostSelectorTest.java

@@ -265,7 +265,7 @@ public class TieredBrokerHostSelectorTest
               .build()
     ).lhs;
 
-    Assert.assertEquals("coldBroker", brokerName);
+    Assert.assertEquals("hotBroker", brokerName);
   }
 
   @Test