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    <p>UPDATE:</p> <p>I'd also put forward <a href="http://msdn.microsoft.com/en-us/library/hh160414.aspx" rel="noreferrer"><code>BufferBlock&lt;T&gt;</code></a> from TPL DataFlow. IIRC it's part of .net now. The great thing about <code>BufferBlock&lt;T&gt;</code> is that you can wait asynchronously for items to become available using the <a href="http://msdn.microsoft.com/en-us/library/hh194836.aspx" rel="noreferrer"><code>Post&lt;T&gt;</code></a> and <a href="http://msdn.microsoft.com/en-us/library/hh194760.aspx" rel="noreferrer"><code>ReceiveAsync&lt;T&gt;</code></a> extension methods. Pretty handy in an async/await world.</p> <p>ORIGINAL ANSWER</p> <p>A while back I faced this problem and came up with a lightweight (rough'n'ready) threadsafe (I hope) pool that has proved very useful, reusable and robust:</p> <pre><code> public class Pool&lt;T&gt; where T : class { private readonly Queue&lt;AsyncResult&lt;T&gt;&gt; asyncQueue = new Queue&lt;AsyncResult&lt;T&gt;&gt;(); private readonly Func&lt;T&gt; createFunction; private readonly HashSet&lt;T&gt; pool; private readonly Action&lt;T&gt; resetFunction; public Pool(Func&lt;T&gt; createFunction, Action&lt;T&gt; resetFunction, int poolCapacity) { this.createFunction = createFunction; this.resetFunction = resetFunction; pool = new HashSet&lt;T&gt;(); CreatePoolItems(poolCapacity); } public Pool(Func&lt;T&gt; createFunction, int poolCapacity) : this(createFunction, null, poolCapacity) { } public int Count { get { return pool.Count; } } private void CreatePoolItems(int numItems) { for (var i = 0; i &lt; numItems; i++) { var item = createFunction(); pool.Add(item); } } public void Push(T item) { if (item == null) { Console.WriteLine("Push-ing null item. ERROR"); throw new ArgumentNullException(); } if (resetFunction != null) { resetFunction(item); } lock (asyncQueue) { if (asyncQueue.Count &gt; 0) { var result = asyncQueue.Dequeue(); result.SetAsCompletedAsync(item); return; } } lock (pool) { pool.Add(item); } } public T Pop() { T item; lock (pool) { if (pool.Count == 0) { return null; } item = pool.First(); pool.Remove(item); } return item; } public IAsyncResult BeginPop(AsyncCallback callback) { var result = new AsyncResult&lt;T&gt;(); result.AsyncCallback = callback; lock (pool) { if (pool.Count == 0) { lock (asyncQueue) { asyncQueue.Enqueue(result); return result; } } var poppedItem = pool.First(); pool.Remove(poppedItem); result.SetAsCompleted(poppedItem); return result; } } public T EndPop(IAsyncResult asyncResult) { var result = (AsyncResult&lt;T&gt;) asyncResult; return result.EndInvoke(); } } </code></pre> <p>In order to avoid any interface requirements of the pooled objects, both the creation and resetting of the objects is performed by user supplied delegates: i.e.</p> <pre><code>Pool&lt;MemoryStream&gt; msPool = new Pool&lt;MemoryStream&gt;(() =&gt; new MemoryStream(2048), pms =&gt; { pms.Position = 0; pms.SetLength(0); }, 500); </code></pre> <p>In the case that the pool is empty, the BeginPop/EndPop pair provide an APM (ish) means of retrieving the object asynchronously when one becomes available (using Jeff Richter's excellent <a href="http://msdn.microsoft.com/en-us/magazine/cc163467.aspx" rel="noreferrer">AsyncResult&lt;TResult&gt;</a> implementation).</p> <p>I can't quite remember why it is constained to T : class... there's probably none.</p>
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    1. COWhy exactly would you use a `HashSet`?
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    2. COy'see, that code is now released under a CC-Wiki license so i can't use it without releasing *my* code under that license, and i'm not sure that i want to do that...
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    3. COI don't understand how the proposed solution is related to the question. It seems like a fancy Queue rather than a ObjectsPool.
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