HADOOP-11209. Configuration#updatingResource/finalParameters are not thread-safe. Contributed by Varun Saxena.

hadoop-common-project/hadoop-common/CHANGES.txt

@@ -741,6 +741,9 @@ Release 2.7.0 - UNRELEASED
     architecture because it is slower there (Suman Somasundar via Colin P.
     McCabe)
 
+    HADOOP-11209. Configuration#updatingResource/finalParameters are not
+    thread-safe. (Varun Saxena via ozawa)
+
 Release 2.6.0 - 2014-11-18
 
   INCOMPATIBLE CHANGES

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/conf/Configuration.java

@@ -52,6 +52,7 @@ import java.util.Properties;
 import java.util.Set;
 import java.util.StringTokenizer;
 import java.util.WeakHashMap;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -228,7 +229,8 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
   /**
    * List of configuration parameters marked <b>final</b>. 
    */
-  private Set<String> finalParameters = new HashSet<String>();
+  private Set<String> finalParameters = Collections.newSetFromMap(
+      new ConcurrentHashMap<String, Boolean>());
   
   private boolean loadDefaults = true;
   
@@ -258,7 +260,7 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
    * Stores the mapping of key to the resource which modifies or loads 
    * the key most recently
    */
-  private HashMap<String, String[]> updatingResource;
+  private Map<String, String[]> updatingResource;
  
   /**
    * Class to keep the information about the keys which replace the deprecated
@@ -685,7 +687,7 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
    */
   public Configuration(boolean loadDefaults) {
     this.loadDefaults = loadDefaults;
-    updatingResource = new HashMap<String, String[]>();
+    updatingResource = new ConcurrentHashMap<String, String[]>();
     synchronized(Configuration.class) {
       REGISTRY.put(this, null);
     }
@@ -708,8 +710,11 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
        this.overlay = (Properties)other.overlay.clone();
      }
 
-     this.updatingResource = new HashMap<String, String[]>(other.updatingResource);
-     this.finalParameters = new HashSet<String>(other.finalParameters);
+     this.updatingResource = new ConcurrentHashMap<String, String[]>(
+         other.updatingResource);
+     this.finalParameters = Collections.newSetFromMap(
+         new ConcurrentHashMap<String, Boolean>());
+     this.finalParameters.addAll(other.finalParameters);
    }
    
     synchronized(Configuration.class) {
@@ -2314,20 +2319,27 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
    * @return final parameter set.
    */
   public Set<String> getFinalParameters() {
-    return new HashSet<String>(finalParameters);
+    Set<String> setFinalParams = Collections.newSetFromMap(
+        new ConcurrentHashMap<String, Boolean>());
+    setFinalParams.addAll(finalParameters);
+    return setFinalParams;
   }
 
   protected synchronized Properties getProps() {
     if (properties == null) {
       properties = new Properties();
-      HashMap<String, String[]> backup = 
-        new HashMap<String, String[]>(updatingResource);
+      Map<String, String[]> backup =
+          new ConcurrentHashMap<String, String[]>(updatingResource);
       loadResources(properties, resources, quietmode);
+
       if (overlay != null) {
         properties.putAll(overlay);
         for (Map.Entry<Object,Object> item: overlay.entrySet()) {
           String key = (String)item.getKey();
-          updatingResource.put(key, backup.get(key));
+          String[] source = backup.get(key);
+          if(source != null) {
+            updatingResource.put(key, source);
+          }
         }
       }
     }
@@ -2579,13 +2591,15 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
           value = DEFAULT_STRING_CHECK;
         }
         properties.setProperty(attr, value);
+        if(source != null) {
           updatingResource.put(attr, source);
+        }
       } else if (!value.equals(properties.getProperty(attr))) {
         LOG.warn(name+":an attempt to override final parameter: "+attr
             +";  Ignoring.");
       }
     }
-    if (finalParameter) {
+    if (finalParameter && attr != null) {
       finalParameters.add(attr);
     }
   }
@@ -2788,9 +2802,11 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
       String value = org.apache.hadoop.io.Text.readString(in);
       set(key, value); 
       String sources[] = WritableUtils.readCompressedStringArray(in);
+      if(sources != null) {
         updatingResource.put(key, sources);
       }
     }
+  }
 
   //@Override
   @Override

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/conf/TestConfiguration.java

@@ -1308,6 +1308,52 @@ public class TestConfiguration extends TestCase {
     assertTrue("my.var is not final", finalParameters.contains("my.var"));
   }
 
+  /**
+   * A test to check whether this thread goes into infinite loop because of
+   * destruction of data structure by resize of Map. This problem was reported
+   * by SPARK-2546.
+   * @throws Exception
+   */
+  public void testConcurrentAccesses() throws Exception {
+    out = new BufferedWriter(new FileWriter(CONFIG));
+    startConfig();
+    declareProperty("some.config", "xyz", "xyz", false);
+    endConfig();
+    Path fileResource = new Path(CONFIG);
+    Configuration conf = new Configuration();
+    conf.addResource(fileResource);
+
+    class ConfigModifyThread extends Thread {
+      final private Configuration config;
+      final private String prefix;
+
+      public ConfigModifyThread(Configuration conf, String prefix) {
+        config = conf;
+        this.prefix = prefix;
+      }
+
+      @Override
+      public void run() {
+        for (int i = 0; i < 100000; i++) {
+          config.set("some.config.value-" + prefix + i, "value");
+        }
+      }
+    }
+
+    ArrayList<ConfigModifyThread> threads = new ArrayList<>();
+    for (int i = 0; i < 100; i++) {
+      threads.add(new ConfigModifyThread(conf, String.valueOf(i)));
+    }
+    for (Thread t: threads) {
+      t.start();
+    }
+    for (Thread t: threads) {
+      t.join();
+    }
+    // If this test completes without going into infinite loop,
+    // it's expected behaviour.
+  }
+
   public static void main(String[] argv) throws Exception {
     junit.textui.TestRunner.main(new String[]{
       TestConfiguration.class.getName()