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copied!<p>Having only 1 thread lock accomplishes nothing. The purpose of the lock is to block <em>other</em> threads, but it doesn't work if no one else checks the lock!</p> <p>Now, you don't need to worry about memory corruption with a 32-bit int, because the <em>write</em> is atomic - but that doesn't necessarily mean you can go lock-free.</p> <p>In your example, it is possible to get questionable semantics:</p> <pre><code>example = 10 Thread A: Add(10) read example (10) Thread B: Read() read example (10) Thread A: write example (10 + 10) </code></pre> <p>which means ThreadB started to read the value of example <em>after</em> thread A began it's update - but read the preupdated value. Whether that's a problem or not depends on what this code is supposed to do, I suppose.</p> <p>Since this is example code, it may be hard to see the problem there. But, imagine the canonical counter function:</p> <pre><code> class Counter { static int nextValue = 0; static IEnumerable<int> GetValues(int count) { var r = Enumerable.Range(nextValue, count); nextValue += count; return r; } } </code></pre> <p>Then, the following scenario:</p> <pre><code> nextValue = 9; Thread A: GetValues(10) r = Enumerable.Range(9, 10) Thread B: GetValues(5) r = Enumerable.Range(9, 5) nextValue += 5 (now equals 14) Thread A: nextValue += 10 (now equals 24) </code></pre> <p>The nextValue is incremented properly, but the ranges returned will overlap. The values of 19 - 24 were never returned. You would fix this by locking around the var r and nextValue assignment to prevent any other thread from executing at the same time.</p>

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