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1. Encapsulation. We don't expose the HashMap instance directly; including its iterators, key set, value set or entry set.
2. We use @Lock(WRITE) on the methods that mutate the map such as the put() and remove() methods.
3. We use @Lock(READ) on the get() and values() methods as they do not change the map state and are guaranteed not to be called at the same as any of the @Lock(WRITE) methods, so we know the state of the HashMap is no being mutated and therefore safe for reading.

The end result is that the threading model for this bean will switch from multi-threaded access to single-threaded access dynamically as needed depending on the which methods are being invoked. This gives Singletons a bit of an advantage over Servlets for processing multi-threaded requests.

Test Case

{snippet:url=openejb3/examples/simple-singleton/src/test/java/org/superbiz/registry/ComponentRegistryBeanTest.java|lang=java|id=code}

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