Author: todd
Date: Thu Mar 22 00:49:06 2012
New Revision: 1303634
URL: http://svn.apache.org/viewvc?rev=1303634&view=rev
Log:
HADOOP-8157. Fix race condition in Configuration that could cause spurious
ClassNotFoundExceptions after a GC. Contributed by Todd Lipcon.
Modified:
hadoop/common/trunk/hadoop-common-project/hadoop-common/CHANGES.txt
hadoop/common/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java
Modified: hadoop/common/trunk/hadoop-common-project/hadoop-common/CHANGES.txt
URL:
http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-common-project/hadoop-common/CHANGES.txt?rev=1303634&r1=1303633&r2=1303634&view=diff
==============================================================================
--- hadoop/common/trunk/hadoop-common-project/hadoop-common/CHANGES.txt
(original)
+++ hadoop/common/trunk/hadoop-common-project/hadoop-common/CHANGES.txt Thu Mar
22 00:49:06 2012
@@ -257,6 +257,9 @@ Release 0.23.3 - UNRELEASED
HADOOP-8191. SshFenceByTcpPort uses netcat incorrectly (todd)
+ HADOOP-8157. Fix race condition in Configuration that could cause spurious
+ ClassNotFoundExceptions after a GC. (todd)
+
BREAKDOWN OF HADOOP-7454 SUBTASKS
HADOOP-7455. HA: Introduce HA Service Protocol Interface. (suresh)
Modified:
hadoop/common/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java
URL:
http://svn.apache.org/viewvc/hadoop/common/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java?rev=1303634&r1=1303633&r2=1303634&view=diff
==============================================================================
---
hadoop/common/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java
(original)
+++
hadoop/common/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java
Thu Mar 22 00:49:06 2012
@@ -190,6 +190,12 @@ public class Configuration implements It
CACHE_CLASSES = new WeakHashMap<ClassLoader, Map<String, Class<?>>>();
/**
+ * Sentinel value to store negative cache results in {@link #CACHE_CLASSES}.
+ */
+ private static final Class<?> NEGATIVE_CACHE_SENTINEL =
+ NegativeCacheSentinel.class;
+
+ /**
* Stores the mapping of key to the resource which modifies or loads
* the key most recently
*/
@@ -1194,24 +1200,24 @@ public class Configuration implements It
}
}
- Class<?> clazz = null;
- if (!map.containsKey(name)) {
+ Class<?> clazz = map.get(name);
+ if (clazz == null) {
try {
clazz = Class.forName(name, true, classLoader);
} catch (ClassNotFoundException e) {
- map.put(name, null); //cache negative that class is not found
+ // Leave a marker that the class isn't found
+ map.put(name, NEGATIVE_CACHE_SENTINEL);
return null;
}
// two putters can race here, but they'll put the same class
map.put(name, clazz);
- } else { // check already performed on this class name
- clazz = map.get(name);
- if (clazz == null) { // found the negative
- return null;
- }
+ return clazz;
+ } else if (clazz == NEGATIVE_CACHE_SENTINEL) {
+ return null; // not found
+ } else {
+ // cache hit
+ return clazz;
}
-
- return clazz;
}
/**
@@ -1915,4 +1921,10 @@ public class Configuration implements It
Configuration.addDeprecation("fs.default.name",
new String[]{CommonConfigurationKeys.FS_DEFAULT_NAME_KEY});
}
+
+ /**
+ * A unique class which is used as a sentinel value in the caching
+ * for getClassByName. {@see Configuration#getClassByNameOrNull(String)}
+ */
+ private static abstract class NegativeCacheSentinel {}
}
