advanced patterns with Concurrent Collections in C# 10 When Using Custom Locking Mechanisms
I'm currently working on a multi-threaded application in C# 10, and I've run into an unexpected scenario with concurrent collections. I’m using `ConcurrentDictionary<TKey, TValue>` to store user session data, but I've implemented a custom locking mechanism to perform batch updates to the dictionary. The question arises when multiple threads attempt to update the same key simultaneously. Instead of the expected behavior where the latest value should overwrite the previous one, I’m observing stale data in my dictionary. Here’s a simplified version of the code that demonstrates the scenario: ```csharp using System; using System.Collections.Concurrent; using System.Threading; using System.Threading.Tasks; class Program { static readonly ConcurrentDictionary<int, string> sessions = new ConcurrentDictionary<int, string>(); static readonly object lockObj = new object(); static void UpdateSession(int key, string value) { lock (lockObj) { sessions[key] = value; } } static void Main() { Parallel.For(0, 10, i => { UpdateSession(1, "Session " + i); }); Console.WriteLine(sessions[1]); // Expected: "Session 9" } } ``` When I run this code, the output can vary, sometimes showing "Session 0" instead of the expected "Session 9". I’ve tried removing the lock and letting `ConcurrentDictionary` handle synchronization, but then I encounter race conditions where updates happen inconsistently. I’ve also ensured that no other parts of the code modify the `sessions` dictionary concurrently. What could be causing this behavior, and how can I ensure that I'm always getting the latest value in the dictionary when multiple threads are attempting to update it? Is there a better pattern or practice I should follow for this scenario?