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POC# How do I update an element in BlockingCollection<T>?
 

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  1. POC# How do I update an element in BlockingCollection<T>?
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    <p>I have a <code>ConcurrentDictionaryWrapper</code> class that wraps <code>ConcurrentDictionary&lt;K,V&gt;</code> and implements the <code>IProducerConsumerCollection</code> interface so I can use it with a <code>BlockingCollection</code>. Producers will add values to the BlockingCollection with a key. The idea is that if the key exists, we replace the value in the underlying dictionary. My <code>ConcurrentDictionaryWrapper.TryAdd()</code> method is as follows:</p> <pre><code>public bool TryAdd(KeyValuePair&lt;TKey, TValue&gt; item) { _wrapped[item.Key] = item.Value return true; } </code></pre> <p>The problem I'm seeing is that if the value is replaced, the BlockingCollection will see this as an addition. </p> <pre><code>var wrapper = new ConcurrentDictionaryWrapper&lt;string, object&gt;(); var bc = new BlockingCollection&lt;KeyValuePair&lt;string, object&gt;&gt;(wrapper); bc.TryAdd(new KeyValuePair&lt;string, object&gt;("key", new object())); bc.TryAdd(new KeyValuePair&lt;string, object&gt;("key", new object())); wrapper.Count; # returns 1 bc.Count; # returns 2 </code></pre> <p>I cannot return false in <code>TryAdd()</code> above because the BlockingCollection will raise an InvalidOperationException.</p> <p>Is there a way to achieve the behaviour I want? I want this to be as simple as possible but there doesn't seem to be a way to have this "AddOrUpdate" behaviour with a BlockingCollection by just implementing <code>IProducerConsumerCollection</code>. I want to avoid having to <code>TryTake()</code> before calling <code>TryAdd()</code> on the BlockingCollection &mdash; I would probably just use a standard lock around a Dictionary and synchronise the producers/consumers with <code>AutoResetEvent</code>.</p>
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