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POWe need to lock a .NET Int32 when reading it in a multithreaded code?
 

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    <p>I was reading the following article: <a href="http://msdn.microsoft.com/en-us/magazine/cc817398.aspx" rel="noreferrer">http://msdn.microsoft.com/en-us/magazine/cc817398.aspx</a> "Solving 11 Likely Problems In Your Multithreaded Code" by Joe Duffy</p> <p>And it raised me a question: "We need to lock a .NET Int32 when reading it in a multithreaded code?"</p> <p>I understand that if it was an Int64 in a 32-bit SO it could tear, as it is explained in the article. But for Int32 I imagined the following situation:</p> <pre><code>class Test { private int example = 0; private Object thisLock = new Object(); public void Add(int another) { lock(thisLock) { example += another; } } public int Read() { return example; } } </code></pre> <p>I don't see a reason to include a lock in the Read method. Do you?</p> <p><strong>Update</strong> Based on the answers (by Jon Skeet and ctacke) I understand that the code above still vulnerable to multiprocessor caching (each processor has its own cache, unsynchronized with others). All the three modifications bellow fix the problem:</p> <ol> <li>Adding to "int example" the "volatile" property</li> <li>Inserting a Thread.MemoryBarrier(); before the actual reading of "int example"</li> <li>Read "int example" inside a "lock(thisLock)"</li> </ol> <p>And I also think that "volatile" is the most elegant solution.</p>
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