From 53e7f73ab9197cfb3f9939b5c2b60c1b4402291b Mon Sep 17 00:00:00 2001
From: Zhihong Yu <tedyu@apache.org>
Date: Mon, 29 Aug 2011 16:00:47 +0000
Subject: [PATCH] HBASE-4278  Race condition in Slab.java that occurs due to
 spinlock unlocking                early (Li Pi)

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1162886 13f79535-47bb-0310-9956-ffa450edef68
---
 CHANGES.txt                                                | 2 ++
 .../java/org/apache/hadoop/hbase/io/hfile/slab/Slab.java   | 7 +++++--
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/CHANGES.txt b/CHANGES.txt
index f21c717abbe..211654e30c3 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -220,6 +220,8 @@ Release 0.91.0 - Unreleased
    HBASE-3229  HBASE-3229 Table creation, though using "async" call to master,
                can actually run for a while and cause RPC timeout (Ming Ma)
    HBASE-4252  TestLogRolling's low-probability failure (Jieshan Bean)
+   HBASE-4278  Race condition in Slab.java that occurs due to spinlock unlocking
+               early (Li Pi)
 
   IMPROVEMENTS
    HBASE-3290  Max Compaction Size (Nicolas Spiegelberg via Stack)  
diff --git a/src/main/java/org/apache/hadoop/hbase/io/hfile/slab/Slab.java b/src/main/java/org/apache/hadoop/hbase/io/hfile/slab/Slab.java
index 69d2662a52d..70781256ba0 100644
--- a/src/main/java/org/apache/hadoop/hbase/io/hfile/slab/Slab.java
+++ b/src/main/java/org/apache/hadoop/hbase/io/hfile/slab/Slab.java
@@ -113,8 +113,11 @@ class Slab implements org.apache.hadoop.hbase.io.HeapSize {
    */
   ByteBuffer alloc(int bufferSize) {
     int newCapacity = Preconditions.checkPositionIndex(bufferSize, blockSize);
-    while (buffers.isEmpty()); // Spinlock
-    ByteBuffer returnedBuffer = buffers.remove();
+
+    ByteBuffer returnedBuffer = buffers.poll();
+    while(returnedBuffer == null){
+      returnedBuffer = buffers.poll();
+    }
     returnedBuffer.clear().limit(newCapacity);
     return returnedBuffer;
   }