From 3727ac9bde3454019cd10afbb74d764e97e02e09 Mon Sep 17 00:00:00 2001
From: Tsz-wo Sze <szetszwo@apache.org>
Date: Wed, 13 Nov 2013 22:50:58 +0000
Subject: [PATCH] HADOOP-10095. In CodecPool, synchronize pool and codecList
 separately in order to reduce lock contention.  Contributed by Nicolas
 Liochon

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1541750 13f79535-47bb-0310-9956-ffa450edef68
---
 .../hadoop-common/CHANGES.txt                 |  3 ++
 .../apache/hadoop/io/compress/CodecPool.java  | 31 ++++++++++---------
 2 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/hadoop-common-project/hadoop-common/CHANGES.txt b/hadoop-common-project/hadoop-common/CHANGES.txt
index 0bec5356dc..e7790f70fc 100644
--- a/hadoop-common-project/hadoop-common/CHANGES.txt
+++ b/hadoop-common-project/hadoop-common/CHANGES.txt
@@ -378,6 +378,9 @@ Release 2.3.0 - UNRELEASED
     HADOOP-9594. Update apache commons math dependency (Timothy St. Clair via
     stevel)
 
+    HADOOP-10095. In CodecPool, synchronize pool and codecList separately in
+    order to reduce lock contention.  (Nicolas Liochon via szetszwo)
+
   OPTIMIZATIONS
 
     HADOOP-9748. Reduce blocking on UGI.ensureInitialized (daryn)
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/CodecPool.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/CodecPool.java
index 63e3a09c30..11d88f13cd 100644
--- a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/CodecPool.java
+++ b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/compress/CodecPool.java
@@ -85,16 +85,15 @@ private static <T> T borrow(Map<Class<T>, List<T>> pool,
     T codec = null;
     
     // Check if an appropriate codec is available
+    List<T> codecList;
     synchronized (pool) {
-      if (pool.containsKey(codecClass)) {
-        List<T> codecList = pool.get(codecClass);
-        
-        if (codecList != null) {
-          synchronized (codecList) {
-            if (!codecList.isEmpty()) {
-              codec = codecList.remove(codecList.size()-1);
-            }
-          }
+      codecList = pool.get(codecClass);
+    }
+
+    if (codecList != null) {
+      synchronized (codecList) {
+        if (!codecList.isEmpty()) {
+          codec = codecList.remove(codecList.size() - 1);
         }
       }
     }
@@ -105,15 +104,17 @@ private static <T> T borrow(Map<Class<T>, List<T>> pool,
   private static <T> void payback(Map<Class<T>, List<T>> pool, T codec) {
     if (codec != null) {
       Class<T> codecClass = ReflectionUtils.getClass(codec);
+      List<T> codecList;
       synchronized (pool) {
-        if (!pool.containsKey(codecClass)) {
-          pool.put(codecClass, new ArrayList<T>());
+        codecList = pool.get(codecClass);
+        if (codecList == null) {
+          codecList = new ArrayList<T>();
+          pool.put(codecClass, codecList);
         }
+      }
 
-        List<T> codecList = pool.get(codecClass);
-        synchronized (codecList) {
-          codecList.add(codec);
-        }
+      synchronized (codecList) {
+        codecList.add(codec);
       }
     }
   }