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copied!<p>Clarification on this answer: This doesn't exactly address the <em>question</em> asked, but the implementation that was linked to above is horribly coded. Perhaps the implementation below would be thread safe.</p> <p>I'm not 100% sure that this is thread safe because I did not test it (and I can't come up with any real world use of this "pattern" because I think it is confusing), but it is a more correct Singleton-like implementation of what you linked to above and might work to accomplish what you wanted. Good luck.</p> <p>Sorry about the <code>Console.WriteLine()</code> calls, I used Snippet Compiler to make this.</p> <pre><code>/// <summary> /// Doubleton /// </summary> public sealed class Doubleton { const int MaxInstances = 2; static volatile Hashtable instances = new Hashtable(); static volatile int PreviousInstanceNumber = MaxInstances; #region Constructor Doubleton() { } #endregion #region Properties /// <summary> /// Get 1 of 2 instances of a Doubleton /// </summary> public static Doubleton Instance { get { lock (instances.SyncRoot) { int instanceNumber = PreviousInstanceNumber == MaxInstances ? 1 : ++PreviousInstanceNumber; // if it doesn't exist, create it if (instances[instanceNumber] == null) { instances[instanceNumber] = new Doubleton(); } PreviousInstanceNumber = instanceNumber; return (Doubleton)instances[instanceNumber]; } } } #endregion /// <summary> /// Get the index of the Doubleton /// </summary> /// <returns></returns> public int GetInstanceIndex() { lock (instances.SyncRoot) { for (int i = 1; i <= MaxInstances; i++) { if (instances[i] != null && instances[i].Equals(this)) { return i; } } } return -1; } } </code></pre> <p>You could then use the following code:</p> <pre><code>var instance1 = Doubleton.Instance; var instance2 = Doubleton.Instance; var instance1Again = Doubleton.Instance; var instance2Again = Doubleton.Instance; Console.WriteLine("The following 2 lines should be true:"); Console.WriteLine(instance1.Equals(instance1Again)); Console.WriteLine(instance2.Equals(instance2Again)); Console.WriteLine("---"); Console.WriteLine("The next 50 lines should alternate instances:"); for (int i = 0; i < 50; i++) { var instance = Doubleton.Instance; Console.WriteLine("I have instance # " + instance.GetInstanceIndex()); } </code></pre>

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