Handling Concurrent Dictionary Updates in C# - advanced patterns with GetOrAdd Method
I'm testing a new approach and I'm refactoring my project and I tried several approaches but none seem to work. I'm experiencing unexpected behavior when using `ConcurrentDictionary<TKey, TValue>.GetOrAdd` in a multi-threaded environment. The goal is to ensure that if a key doesn't exist, it should be added with a default value, but I'm noticing that sometimes it returns `null` even when I expect a value to be present. My dictionary is initialized like this: ```csharp ConcurrentDictionary<int, string> myDictionary = new ConcurrentDictionary<int, string>(); ``` I have the following code that runs in multiple threads: ```csharp var result = myDictionary.GetOrAdd(1, key => { // Simulate some processing that could take time Thread.Sleep(100); return "Value for key " + key; }); ``` Sometimes, I find that the `result` is unexpectedly `null` or I'm seeing multiple threads adding the same key. I am using .NET 6 and I want to ensure that each key is unique and correctly managed. I've also tried wrapping the `GetOrAdd` in a lock, but that defeats the purpose of using `ConcurrentDictionary` for concurrent access. Could anyone suggest what I might be doing wrong or if there's a better pattern to follow to ensure correct behavior in this scenario? This is part of a larger web app I'm building. I'd love to hear your thoughts on this. Any ideas what could be causing this?