👀 Views: 28 💬 Answers: 1 📅 Created: 2025-06-22

c# .net concurrent-collections performance C#

I'm relatively new to this, so bear with me. I'm trying to implement I'm building a feature where I'm relatively new to this, so bear with me....... I'm currently working on a .NET 7 application that heavily relies on `ConcurrentDictionary<TKey, TValue>` for caching user session data. I've noticed that under high load, specifically when handling multiple simultaneous requests, the performance seems to degrade significantly. The application starts throwing `System.InvalidOperationException: Collection was modified; enumeration operation may not execute` errors intermittently when accessing the dictionary. I've implemented the caching mechanism like this: ```csharp var sessionCache = new ConcurrentDictionary<string, UserSession>(); public UserSession GetSession(string sessionId) { if (sessionCache.TryGetValue(sessionId, out var session)) { return session; } // Simulate fetching session from database var newSession = FetchSessionFromDatabase(sessionId); sessionCache[sessionId] = newSession; return newSession; } ``` To test this under load, I’m using a simple load testing tool that sends multiple concurrent requests to the `GetSession` method. The scenario seems to arise particularly when the cache is being populated and accessed simultaneously. I’ve tried wrapping the access in a lock, but that defeats the purpose of using a concurrent collection. I also tried increasing the number of threads in the load test and observed that as the number of threads increases, the exceptions appear more frequently. I’m wondering if there’s a better approach to handle this scenario or if I need to rethink the caching strategy altogether. Any insights or recommendations would be greatly appreciated! What am I doing wrong? I recently upgraded to C# 3.10. I'd be grateful for any help. The project is a web app built with C#. Thanks for your help in advance! What's the correct way to implement this? This issue appeared after updating to C# LTS. Is there a simpler solution I'm overlooking?