From 37abd0e33bedaf19cde73bdbbc31af304cf486a2 Mon Sep 17 00:00:00 2001
From: Kihwal Lee <kihwal@apache.org>
Date: Thu, 5 Nov 2015 09:26:53 -0600
Subject: [PATCH] HDFS-4937. ReplicationMonitor can infinite-loop in
 BlockPlacementPolicyDefault#chooseRandom(). Contributed by Kihwal Lee.
 (cherry picked from commit ff47f35deed14ba6463cba76f0e6a6c15abb3eca)

---
 hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt              | 3 +++
 .../blockmanagement/BlockPlacementPolicyDefault.java     | 9 +++++++++
 2 files changed, 12 insertions(+)

diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index d259e506b74..d3073a9d754 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -1410,6 +1410,9 @@ Release 2.7.3 - UNRELEASED
     HDFS-9289. Make DataStreamer#block thread safe and verify genStamp in
     commitBlock. (Chang Li via zhz)
 
+    HDFS-4937. ReplicationMonitor can infinite-loop in 
+    BlockPlacementPolicyDefault#chooseRandom(). (kihwal)
+
 Release 2.7.2 - UNRELEASED
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyDefault.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyDefault.java
index 56ebc35998a..d94179b3c24 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyDefault.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyDefault.java
@@ -659,6 +659,7 @@ public class BlockPlacementPolicyDefault extends BlockPlacementPolicy {
 
     int numOfAvailableNodes = clusterMap.countNumOfAvailableNodes(
         scope, excludedNodes);
+    int refreshCounter = numOfAvailableNodes;
     StringBuilder builder = null;
     if (LOG.isDebugEnabled()) {
       builder = debugLoggingBuilder.get();
@@ -708,6 +709,14 @@ public class BlockPlacementPolicyDefault extends BlockPlacementPolicy {
         // If no candidate storage was found on this DN then set badTarget.
         badTarget = (storage == null);
       }
+      // Refresh the node count. If the live node count became smaller,
+      // but it is not reflected in this loop, it may loop forever in case
+      // the replicas/rack cannot be satisfied.
+      if (--refreshCounter == 0) {
+        numOfAvailableNodes = clusterMap.countNumOfAvailableNodes(scope,
+            excludedNodes);
+        refreshCounter = numOfAvailableNodes;
+      }
     }
       
     if (numOfReplicas>0) {