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    <p>Your needs seem pretty simple here. The use of MapMaker makes the implementation more complicated than it has to be. The whole double-checked locking idiom is tricky to get right, and only works on 1.5+. And to be honest, it's breaking one of the most important rules of programming:</p> <blockquote> <p>Premature optimization is the root of all evil.</p> </blockquote> <p>The double-checked locking idiom tries to avoid the cost of synchronization in the case where the cache is already loaded. But is that overhead really causing problems? Is it worth the cost of more complex code? I say assume it is not until profiling tells you otherwise.</p> <p>Here's a very simple solution that requires no 3rd party code (ignoring the JCIP annotation). It does make the assumption that an empty list means the cache hasn't been loaded yet. It also prevents the contents of the country list from escaping to client code that could potentially modify the returned list. If this is not a concern for you, you could remove the call to Collections.unmodifiedList().</p> <pre><code>public class CountryList { @GuardedBy("cache") private final List&lt;String&gt; cache = new ArrayList&lt;String&gt;(); private List&lt;String&gt; loadCountryList() { // HEAVY OPERATION TO LOAD DATA } public List&lt;String&gt; list() { synchronized (cache) { if( cache.isEmpty() ) { cache.addAll(loadCountryList()); } return Collections.unmodifiableList(cache); } } public void invalidateCache() { synchronized (cache) { cache.clear(); } } } </code></pre>
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