[jira] [Created] (HADOOP-10513) ReflectionUtils::CONSTRUCTOR_CACHE leaks class loaders

["Gopal V (JIRA)" <ji...@apache.org>]

Gopal V created HADOOP-10513:
--------------------------------

             Summary: ReflectionUtils::CONSTRUCTOR_CACHE leaks class loaders
                 Key: HADOOP-10513
                 URL: https://issues.apache.org/jira/browse/HADOOP-10513
             Project: Hadoop Common
          Issue Type: Bug
          Components: util
    Affects Versions: 2.4.0
            Reporter: Gopal V


Any code which uses custom class-loaders needs to be aware of the ReflectionUtils::CONSTRUCTOR_CACHE 

{code}
 /** 
   * Cache of constructors for each class. Pins the classes so they
   * can't be garbage collected until ReflectionUtils can be collected.
   */
  private static final Map<Class<?>, Constructor<?>> CONSTRUCTOR_CACHE = 
    new ConcurrentHashMap<Class<?>, Constructor<?>>();
{code}

This is not a problem when using only 1 AppClassLoader.

But in cases where the application uses multiple classloaders (to isolate UDFs), this holds onto class references and their associated class loaders by ref (& that leaks all the statics).

The clear method for this cache is unfortunately marked only for testing.

{code}
  // methods to support testing
  static void clearCache() {
    CONSTRUCTOR_CACHE.clear();
  }
{code}

The cache shows up as the only reference for the class loaders.

!class-loader-leak.png!



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