HADOOP-15331. Fix a race condition causing parsing error of java.io.BufferedInputStream in class org.apache.hadoop.conf.Configuration. Contributed by Miklos Szegedi.

(cherry picked from commit 268c29a5f541449659f4b4ea1975c6f04c7b6a70)

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

@@ -768,8 +768,11 @@ public class Configuration implements Iterable<Map.Entry<String,String>>,
    */
   @SuppressWarnings("unchecked")
   public Configuration(Configuration other) {
-    this.resources = (ArrayList<Resource>) other.resources.clone();
     synchronized(other) {
+      // Make sure we clone a finalized state
+      // Resources like input streams can be processed only once
+      other.getProps();
+      this.resources = (ArrayList<Resource>) other.resources.clone();
       if (other.properties != null) {
         this.properties = (Properties)other.properties.clone();
       }

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

@@ -2142,4 +2142,34 @@ public class TestConfiguration extends TestCase {
     assertEquals("  prefix >cdata\nsuffix  ", conf.get("cdata-whitespace"));
     return conf;
   }
+
+  /**
+   * Test race conditions between clone() and getProps().
+   * Test for race conditions in the way Hadoop handles the Configuration
+   * class. The scenario is the following. Let's assume that there are two
+   * threads sharing the same Configuration class. One adds some resources
+   * to the configuration, while the other one clones it. Resources are
+   * loaded lazily in a deferred call to loadResources(). If the cloning
+   * happens after adding the resources but before parsing them, some temporary
+   * resources like input stream pointers are cloned. Eventually both copies
+   * will load the same input stream resources.
+   * One parses the input stream XML and closes it updating it's own copy of
+   * the resource. The other one has another pointer to the same input stream.
+   * When it tries to load it, it will crash with a stream closed exception.
+   */
+  @Test
+  public void testResourceRace() {
+    InputStream is =
+        new BufferedInputStream(new ByteArrayInputStream(
+            "<configuration></configuration>".getBytes()));
+    Configuration config = new Configuration();
+    // Thread 1
+    config.addResource(is);
+    // Thread 2
+    Configuration confClone = new Configuration(conf);
+    // Thread 2
+    confClone.get("firstParse");
+    // Thread 1
+    config.get("secondParse");
+  }
 }