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copied!<blockquote> <p>Is the following safe when the proxiedObject is being acceessed by multiple threads?</p> </blockquote> <p>No, unless <code>mo</code> is <code>volatile</code>. If the <code>mo</code> field is <code>volatile</code> then this will properly cross a memory barrier and the updates to the <code>mo</code> field will be seen by all threads.</p> <p>It is important to realize that if the <code>MyObject</code> is not immutable, additional concurrency issues will result even if <code>mo</code> is <code>volatile</code>.</p> <hr> <p><strong>Edit:</strong></p> <p>Thanks to @jtahlborn comments on this. I've been doing some reading and I'm now pretty sure that the <code>volatile</code> will <em>also</em> protect the <code>MyObject</code> from being partially initialized.</p> <p>Due to <a href="http://www.ibm.com/developerworks/java/library/j-jtp0618/index.html" rel="nofollow noreferrer">constructor instruction reordering possibilities</a>, there is no guarantee that the <code>MyObject</code> has been fulling constructed when its referenced is shared between threads. Only <code>final</code> fields in a constructor are guaranteed to be properly initialized when a constructor finishes. Any other fields may or may not have been initialized and so you will need to synchronize on the object before the multiple threads can start accessing it.</p> <p>However, if the<code>mo</code> field is volatile, then the "happens before" guarantee also ensures that the <code>MyObject</code> has been fully initialized. The compiler is not allowed to reorder those instructions past the publishing of a <code>volatile</code> variable. See:</p> <ul> <li><a href="http://jeremymanson.blogspot.com/2008/11/what-volatile-means-in-java.html" rel="nofollow noreferrer">What Volatile Means In Java</a></li> <li><a href="https://stackoverflow.com/questions/2441279/java-volatile-guarantees-and-out-of-order-execution">Volatile guarantees and out-of-order execution</a></li> </ul>

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