From a89baed8332e5b276b55379b1900833366e1695a Mon Sep 17 00:00:00 2001
From: Todd Lipcon <todd@apache.org>
Date: Sun, 18 Dec 2011 01:13:00 +0000
Subject: [PATCH] HDFS-2553. Fix BlockPoolSliceScanner spinning in a tight
 loop. Contributed by Uma Maheswara Rao G.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1220317 13f79535-47bb-0310-9956-ffa450edef68
---
 hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt            |  3 +++
 .../hdfs/server/datanode/BlockPoolSliceScanner.java    | 10 +++++-----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
index dc8d4b0be9f..c7bd4272336 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
+++ b/hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt
@@ -275,6 +275,9 @@ Release 0.23.1 - UNRELEASED
 
     HDFS-2640. Javadoc generation hangs. (tomwhite)
 
+    HDFS-2553. Fix BlockPoolSliceScanner spinning in a tight loop (Uma
+    Maheswara Rao G via todd)
+
 Release 0.23.0 - 2011-11-01 
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockPoolSliceScanner.java b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockPoolSliceScanner.java
index a666149beb1..1f45a7bb561 100644
--- a/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockPoolSliceScanner.java
+++ b/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/BlockPoolSliceScanner.java
@@ -450,14 +450,14 @@ class BlockPoolSliceScanner {
   }
   
   private synchronized long getEarliestScanTime() {
-    if ( blockInfoSet.size() > 0 ) {
+    if (!blockInfoSet.isEmpty()) {
       return blockInfoSet.first().lastScanTime;
     }
     return Long.MAX_VALUE; 
   }
   
   private synchronized boolean isFirstBlockProcessed() {
-    if (blockInfoSet.size() > 0 ) {
+    if (!blockInfoSet.isEmpty()) {
       long blockId = blockInfoSet.first().block.getBlockId();
       if ((processedBlocks.get(blockId) != null)
           && (processedBlocks.get(blockId) == 1)) {
@@ -471,7 +471,7 @@ class BlockPoolSliceScanner {
   private void verifyFirstBlock() {
     Block block = null;
     synchronized (this) {
-      if ( blockInfoSet.size() > 0 ) {
+      if (!blockInfoSet.isEmpty()) {
         block = blockInfoSet.first().block;
       }
     }
@@ -560,7 +560,7 @@ class BlockPoolSliceScanner {
      * lastModificationTime > 0.
      */    
     synchronized (this) {
-      if (blockInfoSet.size() > 0 ) {
+      if (!blockInfoSet.isEmpty()) {
         BlockScanInfo info;
         while ((info =  blockInfoSet.first()).lastScanTime < 0) {
           delBlockInfo(info);        
@@ -630,7 +630,7 @@ class BlockPoolSliceScanner {
           }
         }
         if (((now - getEarliestScanTime()) >= scanPeriod)
-            || (!(this.isFirstBlockProcessed()))) {
+            || ((!blockInfoSet.isEmpty()) && !(this.isFirstBlockProcessed()))) {
           verifyFirstBlock();
         } else {
           if (LOG.isDebugEnabled()) {