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copied!<p>The point is: it might work, but it isn't <strong>guaranteed</strong> to work by the spec. What people are usually after is code that works for the right reasons, rather than working by a fluke combination of the compiler, the runtime and the JIT, which <em>might</em> change between framework versions, the physical CPU, the platform, and things like x86 vs x64.</p> <p>Understanding the memory model is a very very complex area, and I don't claim to be an expert; but people who <strong>are</strong> real experts in this area assure me that the behaviour you are seeing is not guaranteed.</p> <p>You can post as many working examples as you like, but unfortunately that doesn't prove much other than "it usually works". It certainly doesn't prove that it is <strong>guaranteed</strong> to work. It would only take a single counter-example to disprove, but finding it is the problem...</p> <p><s>No, I don't have one to hand.</s></p> <hr> <p>Update with repeatable counter-example:</p> <pre><code>using System.Threading; using System; static class BackgroundTaskDemo { // make this volatile to fix it private static bool stopping = false; static void Main() { new Thread(DoWork).Start(); Thread.Sleep(5000); stopping = true; Console.WriteLine("Main exit"); Console.ReadLine(); } static void DoWork() { int i = 0; while (!stopping) { i++; } Console.WriteLine("DoWork exit " + i); } } </code></pre> <p>Output:</p> <pre><code>Main exit </code></pre> <p>but still running, at full CPU; note that <code>stopping</code> has been set to <code>true</code> by this point. The <code>ReadLine</code> is so that the process doesn't terminate. The optimization seems to be dependent on the size of the code inside the loop (hence <code>i++</code>). It only works in "release" mode obviously. Add <code>volatile</code> and it all works fine.</p>

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