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copied!<p>For the fun of it, here is a lock-free implementation:</p> <pre><code>public sealed class MessageWrapper { private int pendingB; public Message WrapA(int a, int millisecondsTimeout) { int b = Interlocked.Exchange(ref pendingB, -1); return new Message(a, b == -1 ? null : b); } public Message WrapB(int b, int millisecondsTimeout) { var sw = new SpinWait(); while (Interlocked.CompareExchange(ref pendingB, b, -1) != -1) { // Spin sw.SpinOnce(); if (sw.NextSpinWillYield) { // Let us make progress instead of yielding the processor // (avoid context switch) return new Message(null, b); } } return null; } } </code></pre> <p><strong>Results</strong></p> <p>Original implementation:</p> <pre><code>00:00:02.0433298 0: 0 A: 733 B: 233 AB: 67 Generated A: 800, Sent A: 800 Generated B: 300, Sent B: 300 </code></pre> <p>Lock-free implementation:</p> <pre><code>00:00:01.2546310 0: 0 A: 717 B: 217 AB: 83 Generated A: 800, Sent A: 800 Generated B: 300, Sent B: 300 </code></pre> <p><strong>Update</strong></p> <p>Unfortunately, above implementation has a bug plus some shortcoming. Here is an improved version:</p> <pre><code>public class MessageWrapper { private int pendingB = EMPTY; private const int EMPTY = -1; public Message WrapA(int a, int millisecondsTimeout) { int? b; int count = 0; while ((b = Interlocked.Exchange(ref pendingB, EMPTY)) == EMPTY) { if (count % 7 == 0) { Thread.Sleep(0); } else if (count % 23 == 0) { Thread.Sleep(1); } else { Thread.Yield(); } if (++count == 480) { return new Message(a, null); } } return new Message(a, b); } public Message WrapB(int b, int millisecondsTimeout) { int count = 0; while (Interlocked.CompareExchange(ref pendingB, b, EMPTY) != EMPTY) { // Spin Thread.SpinWait((4 << count++)); if (count > 10) { // We didn't manage to place our payload. // Let's send it ourselves: return new Message(null, b); } } // We placed our payload. // Wait some more to see if some WrapA snatches it. while (Interlocked.CompareExchange(ref pendingB, EMPTY, EMPTY) == b) { Thread.SpinWait((4 << count++)); if (count > 20) { // No WrapA came along. Pity, we will have to send it ourselves int payload = Interlocked.CompareExchange(ref pendingB, EMPTY, b); return payload == b ? new Message(null, b) : null; } } return null; } } </code></pre> <p>Results:</p> <p>OP's implementation</p> <pre><code>00:00:02.1389474 0: 0 A: 722 B: 222 AB: 78 Generated A: 800, Sent A: 800 Generated B: 300, Sent B: 300 </code></pre> <p>Second implementation:</p> <pre><code>00:00:01.2752425 0: 0 A: 700 B: 200 AB: 100 Generated A: 800, Sent A: 800 Generated B: 300, Sent B: 300 </code></pre>

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