From 0c8c763e431d3c923f3db04b9ecd32aef1b94450 Mon Sep 17 00:00:00 2001
From: Stuart Douglas <stuart.w.douglas@gmail.com>
Date: Tue, 3 Dec 2013 16:13:40 +0100
Subject: [PATCH] Use double checked locking to remove sync block

---
 .../jackson/databind/ser/SerializerCache.java      | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/main/java/com/fasterxml/jackson/databind/ser/SerializerCache.java b/src/main/java/com/fasterxml/jackson/databind/ser/SerializerCache.java
index 0d4b1f26e7..8f7cc5c72c 100644
--- a/src/main/java/com/fasterxml/jackson/databind/ser/SerializerCache.java
+++ b/src/main/java/com/fasterxml/jackson/databind/ser/SerializerCache.java
@@ -33,7 +33,7 @@ public final class SerializerCache
     /**
      * Most recent read-only instance, created from _sharedMap, if any.
      */
-    private ReadOnlyClassToSerializerMap _readOnlyMap = null;
+    private volatile ReadOnlyClassToSerializerMap _readOnlyMap = null;
 
     public SerializerCache() { }
 
@@ -43,11 +43,13 @@ public SerializerCache() { }
      */
     public ReadOnlyClassToSerializerMap getReadOnlyLookupMap()
     {
-        ReadOnlyClassToSerializerMap m;
-        synchronized (this) {
-            m = _readOnlyMap;
-            if (m == null) {
-                _readOnlyMap = m = ReadOnlyClassToSerializerMap.from(_sharedMap);
+        ReadOnlyClassToSerializerMap m = _readOnlyMap;
+        if(m == null) {
+            synchronized (this) {
+                m = _readOnlyMap;
+                if (m == null) {
+                    _readOnlyMap = m = ReadOnlyClassToSerializerMap.from(_sharedMap);
+                }
             }
         }
         return m.instance();