👀 Views: 0 💬 Answers: 1 📅 Created: 2025-06-06

c# async concurrentdictionary threading asynchronous

I'm encountering an unexpected behavior when using `ConcurrentDictionary<TKey, TValue>` in my C# 9 application, particularly when accessing it within asynchronous methods. My goal is to store user sessions based on their IDs, but I'm seeing that some entries appear to be overwritten or not retrieved correctly. Here’s a simplified version of my code: ```csharp public class SessionManager { private readonly ConcurrentDictionary<string, UserSession> _sessions = new(); public async Task AddSessionAsync(string userId, UserSession session) { _sessions[userId] = session; await Task.Delay(100); // Simulating async work } public async Task<UserSession> GetSessionAsync(string userId) { await Task.Delay(50); // Simulating async work return _sessions.TryGetValue(userId, out var session) ? session : null; } } ``` I use this `SessionManager` class in the following way: ```csharp public async Task ProcessUser(string userId) { var session = new UserSession { UserId = userId, LastAccessTime = DateTime.UtcNow }; await _sessionManager.AddSessionAsync(userId, session); var retrievedSession = await _sessionManager.GetSessionAsync(userId); // Do something with retrievedSession... } ``` However, I noticed that sometimes `retrievedSession` is null, even after I just added it. I'm not sure if this is due to the asynchronous nature of the operations or if there's a problem with accessing the `ConcurrentDictionary`. I tested the addition of sessions sequentially, and it worked correctly, but when multiple users are processed concurrently, it fails. Could this be a race condition, or am I missing something about how `ConcurrentDictionary` works? Any guidance on best practices for managing concurrent operations with this structure would be greatly appreciated.