Michael Pradel created OPENJPA-2243:
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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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