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From "Michael Pradel (JIRA)" <j...@apache.org>
Subject [jira] [Created] (OPENJPA-2243) Deadlock involving FormatPreservingProperties
Date Fri, 27 Jul 2012 10:03:34 GMT
Michael Pradel created OPENJPA-2243:
---------------------------------------

             Summary: Deadlock involving FormatPreservingProperties
                 Key: OPENJPA-2243
                 URL: https://issues.apache.org/jira/browse/OPENJPA-2243
             Project: OpenJPA
          Issue Type: Bug
          Components: lib
    Affects Versions: 2.2.0
         Environment: All environments
            Reporter: Michael Pradel


FormatPreservingProperties extends Properties, which is a thread-safe class, but it does not
preserve the thread safety. This leads to surprising deadlocks if you have a reference of
type Properties, because it may turn out to be not thread-safe (despite being documented as
such).

Here's a simplified example that shows how we hit this bug:

final Properties p1 = new Properties();
final Properties p2 = createPropsWithDefault(p1);
p2.put(p2, p2);
		
Thread t1 = new Thread(new Runnable() {
  public void run() { p2.remove(p1); }
});

Thread t2 = new Thread(new Runnable() {
  public void run() { p2.stringPropertyNames(); }
});
t1.start();
t2.start();
try { t1.join(); t2.join();
} catch (InterruptedException e) { e.printStackTrace(); }

Properties createPropsWithDefault(Properties p) {
  // return new Properties(p); // OK 
  return new FormatPreservingProperties(p); // leads to deadlock
}


If createPropsWithDefault() returns Properties, everything is OK (as it should be, because
Properties is thread-safe). However, if it returns FormatPreservingProperties, we occasionally
get a deadlock.

Are you aware of this inconsistency? It seems that the safest way of extending Properties
is to make methods that override synchronized methods synchronized.


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