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copied!<p>Well, you don't need <em>locks</em> necessarily - but if you want one thread to definitely read the value that another thread has written, you either need locks or a volatile variable.</p> <p>I've personally given up trying to understand the precise meaning of volatile. I try to avoid writing my own lock-free code, instead relying on experts who really understand the memory model.</p> <p>EDIT: As an example of the kind of problem this can cause, consider this code:</p> <pre><code>using System; using System.Threading; public class Test { private static bool stop = false; private bool Stop { get { return stop; } set { stop = value; } } private static void Main() { Thread t = new Thread(DoWork); t.Start(); Thread.Sleep(1000); // Let it get started Console.WriteLine("Setting stop flag"); Stop = true; Console.WriteLine("Set"); t.Join(); } private static void DoWork() { Console.WriteLine("Tight looping..."); while (!Stop) { } Console.WriteLine("Done."); } } </code></pre> <p>That program <em>may or may not</em> terminate. I've seen both happen. There's no guarantee that the "reading" thread will <em>actually</em> read from main memory - it can put the initial value of <code>stop</code> into a register and just keep using that forever. I've seen that happen, in reality. It doesn't happen on my current machines, but it may do on my next.</p> <p>Putting locks within the property getter/setter as per the code in the question would make this code correct and its behaviour predictable.</p> <p>For more on this, see this <a href="http://blogs.msdn.com/b/ericlippert/archive/2011/06/16/atomicity-volatility-and-immutability-are-different-part-three.aspx" rel="noreferrer">blog post by Eric Lippert</a>.</p>

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