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https://issues.apache.org/jira/browse/OPENJPA-2243?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Albert Lee updated OPENJPA-2243:
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Attachment: OPENJPA-2243.patch
> 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
> Attachments: OPENJPA-2243.patch
>
>
> 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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