wrapping classes with WeakRefs in CLASS_CACHE

HADOOP-8632
costin · Aug 16, 2012 · 518c398 · 518c398
1 parent 7a3427d
commit 518c398
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Showing 2 changed files with 20 additions and 7 deletions.
diff --git a/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java b/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java
@@ -30,6 +30,7 @@
 import java.io.OutputStreamWriter;
 import java.io.Reader;
 import java.io.Writer;
+import java.lang.ref.WeakReference;
 import java.net.InetSocketAddress;
 import java.net.URL;
 import java.util.ArrayList;
@@ -219,8 +220,8 @@ public String toString() {
   private static final CopyOnWriteArrayList<String> defaultResources =
     new CopyOnWriteArrayList<String>();
 
-  private static final Map<ClassLoader, Map<String, Class<?>>>
-    CACHE_CLASSES = new WeakHashMap<ClassLoader, Map<String, Class<?>>>();
+  private static final Map<ClassLoader, Map<String, WeakReference<Class<?>>>>
+    CACHE_CLASSES = new WeakHashMap<ClassLoader, Map<String, WeakReference<Class<?>>>>();
 
   /**
    * Sentinel value to store negative cache results in {@link #CACHE_CLASSES}.
@@ -1531,28 +1532,33 @@ public Class<?> getClassByName(String name) throws ClassNotFoundException {
    * @return the class object, or null if it could not be found.
    */
   public Class<?> getClassByNameOrNull(String name) {
-    Map<String, Class<?>> map;
+    Map<String, WeakReference<Class<?>>> map;
 
     synchronized (CACHE_CLASSES) {
       map = CACHE_CLASSES.get(classLoader);
       if (map == null) {
         map = Collections.synchronizedMap(
-          new WeakHashMap<String, Class<?>>());
+          new WeakHashMap<String, WeakReference<Class<?>>>());
         CACHE_CLASSES.put(classLoader, map);
       }
     }
 
-    Class<?> clazz = map.get(name);
+    Class<?> clazz = null;
+    WeakReference<Class<?>> ref = map.get(name); 
+    if (ref != null) {
+    	clazz = ref.get();
+    }
+
     if (clazz == null) {
       try {
         clazz = Class.forName(name, true, classLoader);
       } catch (ClassNotFoundException e) {
         // Leave a marker that the class isn't found
-        map.put(name, NEGATIVE_CACHE_SENTINEL);
+        map.put(name, new WeakReference<Class<?>>(NEGATIVE_CACHE_SENTINEL));
         return null;
       }
       // two putters can race here, but they'll put the same class
-      map.put(name, clazz);
+      map.put(name, new WeakReference<Class<?>>(clazz));
       return clazz;
     } else if (clazz == NEGATIVE_CACHE_SENTINEL) {
       return null; // not found

diff --git a/...-common-project/hadoop-common/src/test/java/org/apache/hadoop/conf/TestConfiguration.java b/...-common-project/hadoop-common/src/test/java/org/apache/hadoop/conf/TestConfiguration.java
@@ -39,6 +39,7 @@
 
 import junit.framework.TestCase;
 import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertNotNull;
 
 import org.apache.commons.lang.StringUtils;
 import org.apache.hadoop.conf.Configuration.IntegerRanges;
@@ -1157,6 +1158,12 @@ public void testSetPattern() {
         configuration.getPattern("testPattern", Pattern.compile("")).pattern());
   }
 
+  public void testGetClassByNameOrNull() throws Exception {
+	Configuration config = new Configuration();
+	Class<?> clazz = config.getClassByNameOrNull("java.lang.Object");
+	assertNotNull(clazz);
+  }
+
   public static void main(String[] argv) throws Exception {
     junit.textui.TestRunner.main(new String[]{
       TestConfiguration.class.getName()