期限付き Lazy

TtlLazy.cs

public class TtlLazy<T> {
    private readonly Func<T> _factory;
    private readonly TimeSpan _ttl;

    private T _value = default!;
    private bool _initialized;
    private object? _lock;

    public TtlLazy(Func<T> factory, TimeSpan ttl) {
        _factory = factory ?? throw new ArgumentNullException(nameof(factory));
        _ttl = ttl;
    }

    public T Value => LazyInitializer.EnsureInitialized(ref _value, ref _initialized, ref _lock, () => {
        Task.Delay(_ttl).ContinueWith(_ => _initialized = false);

        return _factory();
    });

    public bool IsValueCreated => _initialized;
    public TimeSpan Ttl => _ttl;
}

Usage.cs

async Task Main() {
    TtlLazy<int> cache = new(() => {
        return Random.Shared.Next();
    }, TimeSpan.FromSeconds(0.1));
    
    for (int i = 0; i < 100; i++) {
        await Task.Delay(10).ConfigureAwait(false);
        (cache.Value + "@" + Thread.CurrentThread.ManagedThreadId).Dump();
    }
}