C# - How can I prevent duplicate entries when adding to a Dictionary in a multi-threaded environment?
I'm writing unit tests and I'm working on a project and hit a roadblock. I'm working on a C# application where I need to populate a `Dictionary<TKey, TValue>` from multiple threads. However, I'm working with a `System.ArgumentException` with the message "An item with the same key has already been added." This occurs when two threads attempt to add the same key simultaneously. To tackle this, I initially tried using a `lock` statement to synchronize the access to the dictionary, but I'm still experiencing issues with performance due to the locking overhead. Here’s a snippet of what I currently have: ```csharp private Dictionary<int, string> myDictionary = new Dictionary<int, string>(); private readonly object dictLock = new object(); public void AddToDictionary(int key, string value) { lock (dictLock) { myDictionary.Add(key, value); } } ``` While this approach prevents the exceptions, it causes important performance degradation, especially with a large number of threads. I also considered using `ConcurrentDictionary<TKey, TValue>`, but I’m unsure if it provides the level of control I need over adding entries. How can I efficiently manage concurrent writes to a dictionary without running into duplicate keys, while maintaining good performance? Any best practices or alternative approaches would be greatly appreciated. For context: I'm using C# on Windows. I'm coming from a different tech stack and learning C#. Any examples would be super helpful.