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    <p>Volatile can be a performance option in some cases to avoid the additional hit of using a lock, but it doesn't address threadsafety issues of race conditions, which your third example (the one at question) has.</p> <p>To make sure an uninitialized instance is not retrieved by another thread you should not assign to the static variable until you have a completely initialized instance. Then as soon as they see a non-null, they know it's good. <strong>Edited</strong>: (correction) While I think it's more ideal to avoid redundant work (below), I guess allowing regeneration and replacement of the static reference (as you had it, or Guffa's version) is still "safe" for your use case because each reference to <code>GetMyObject()</code> will grab the single object in place at the time.</p> <p>I would suggest something like this:</p> <pre><code>private static object s_Lock = new object(); private static volatile MyObject s_MyObject; private static MyObject LoadMyObject() { MyObject myObject = new MyObject(); myObject.Initialize(); return myObject; } public static MyObject GetMyObject() { if (s_MyObject == null) { lock (s_Lock) { if (s_MyObject == null) // Check again now that we're in the lock. s_MyObject = LoadMyObject(); // Only one access does this work. } } return s_MyObject; // Once it's set, it's never cleared or assigned again. } </code></pre> <p>This has the advantage of only doing the init work once, but also avoiding the lock contention overhead unless it's actually needed... while still being threadsafe. (You could use volatile as above if you want to be sure it propagates out, but this should also "work" without it; it would just be more likley to need the lock before seeing the new contents of <code>s_MyObject</code>, depending on the architecture. So I think volatile is helpful for this approach.)</p> <p>I've kept your <code>LoadMyObject</code> and <code>GetMyObject</code> methods, but you could also combine the logic into the then clause of the inner if for a single factory method.</p>
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    1. POIs this thread-safe?
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    1. CO+1 for the suggestion of the double checked locking pattern. Although in this instance the questioner doesn't mind multiple instances if you do this is the way to go.
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      1. USPaul Arnold
    2. COThread-safety aside, the performance hit of making redundant instances would almost surely be more than the impact of this mimimal lock pattern (although both could be small). But I guess it's not technically needed for minimal thread-safety in his scenario.
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