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POHow can one break this (non?) thread safe object?
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  1. POHow can one break this (non?) thread safe object?
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    copied!<p>I replied to a <a href="https://stackoverflow.com/questions/9621260/thread-safety-of-a-fluent-like-class-using-clone-and-non-final-fields/9621337#9621337">question</a> earlier about thread safety which did not get a definite answer (I think).</p> <p>So I have been trying to convince myself that the design is broken (visibility) by having thousands of threads read and write that object - but I have not been able to get anything unexpected. That is obviously not a proof that it is thread safe, probably merely a proof of my own limitations!</p> <p>I understand the risk of reordering but I don't see how it could apply in that case, in the sense that the <code>clone</code> instance in the <code>bar()</code> method is local and the change on its fields is done before being released to the outside world with <code>return</code>, after which the instance is effectively immutable. So a thread looking at the returned object would see it with its <code>bar</code> field already set to the correct value...</p> <p><strong>So my question is:</strong> <s>what kind of code</s> Could you show a piece of code that uses <code>IsItSafe</code> and that could lead 2 threads to see different values of the <code>bar</code> field of a given instance of <code>IsItSafe</code>?</p> <p>For reference and ease of reading I copy the code here:</p> <pre><code>public class IsItSafe implements Cloneable { private int foo; private int bar; public IsItSafe foo(int foo) { IsItSafe clone = clone(); clone.foo = foo; return clone; } public IsItSafe bar(int bar) { IsItSafe clone = clone(); clone.bar = bar; return clone; } public int getFoo() { return foo; } public int getBar() { return bar; } protected IsItSafe clone() { try { return (IsItSafe) super.clone(); } catch (CloneNotSupportedException e) { throw new Error(e); } } } </code></pre>
 

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