YARN-1724. Race condition in Fair Scheduler when continuous scheduling is turned on (Sandy Ryza)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1569447 13f79535-47bb-0310-9956-ffa450edef68

hadoop-yarn-project/CHANGES.txt

@@ -292,6 +292,9 @@ Release 2.4.0 - UNRELEASED
     YARN-1721. When moving app between queues in Fair Scheduler, grab lock on
     FSSchedulerApp (Sandy Ryza)
 
+    YARN-1724. Race condition in Fair Scheduler when continuous scheduling is
+    turned on (Sandy Ryza)
+
 Release 2.3.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/fair/FairScheduler.java

@@ -989,7 +989,13 @@ public class FairScheduler extends AbstractYarnScheduler {
   private void continuousScheduling() {
     while (true) {
       List<NodeId> nodeIdList = new ArrayList<NodeId>(nodes.keySet());
-      Collections.sort(nodeIdList, nodeAvailableResourceComparator);
+      // Sort the nodes by space available on them, so that we offer
+      // containers on emptier nodes first, facilitating an even spread. This
+      // requires holding the scheduler lock, so that the space available on a
+      // node doesn't change during the sort.
+      synchronized (this) {
+        Collections.sort(nodeIdList, nodeAvailableResourceComparator);
+      }
 
       // iterate all nodes
       for (NodeId nodeId : nodeIdList) {