Issue with Lazy Initialization of a Singleton in C# - Thread Safety Concerns
I need some guidance on I've been working on this all day and I'm having trouble with lazy initialization of a singleton class in C#... I want to ensure that my implementation is thread-safe, but I'm encountering unexpected behaviors. Here’s the implementation I started with: ```csharp public class Singleton { private static Singleton _instance; private static readonly object _lock = new object(); private Singleton() { } public static Singleton Instance { get { if (_instance == null) { lock (_lock) { if (_instance == null) { _instance = new Singleton(); } } } return _instance; } } } ``` While this code compiles and runs, I'm occasionally experiencing issues when multiple threads access the `Instance` property simultaneously. Sometimes it seems like two instances of `Singleton` are created, leading to inconsistent application behavior. I tried using the `Lazy<T>` class for a more straightforward implementation: ```csharp public class Singleton { private static readonly Lazy<Singleton> _instance = new Lazy<Singleton>(() => new Singleton()); private Singleton() { } public static Singleton Instance => _instance.Value; } ``` This approach seems cleaner and avoids the manual locking, but I still see some threading problems when running tests that heavily rely on parallel access to `Singleton.Instance`. My application is running on .NET 6, and I’m using `Task.Run` in various places to simulate concurrent access. Here's a snippet of how I'm testing it: ```csharp Parallel.For(0, 10, i => { var instance = Singleton.Instance; Console.WriteLine(instance.GetHashCode()); }); ``` What could be causing these intermittent issues? Is it possible that the Lazy initialization can still lead to race conditions, or are there other best practices I should be considering for singleton implementations in a multi-threaded environment? Any insights would be appreciated! This issue appeared after updating to C# stable.