README.md

Soenneker.Utils.AsyncSingleton

An externally initializing singleton that uses double-check asynchronous locking, with optional async and sync disposal

Installation

dotnet add package Soenneker.Utils.AsyncSingleton

Example

The example below is a long-living HttpClient implementation using AsyncSingleton. It avoids the additional overhead of IHttpClientFactory, and doesn't rely on short-lived clients.

public class HttpRequester : IDisposable, IAsyncDisposable
{
    private readonly AsyncSingleton<HttpClient> _client;

    public HttpRequester()
    {
        // This func will lazily execute once it's retrieved the first time.
        // Other threads calling this at the same moment will asynchronously wait,
        // and then utilize the HttpClient that was created from the first caller.
        _client = new AsyncSingleton<HttpClient>(() =>
        {
            var socketsHandler = new SocketsHttpHandler
            {
                PooledConnectionLifetime = TimeSpan.FromMinutes(10),
                MaxConnectionsPerServer = 10
            };

            return new HttpClient(socketsHandler);
        });
    }

    public async ValueTask Get()
    {
        // retrieve the singleton async, thus not blocking the calling thread
        await (await _client.Get()).GetAsync("https://google.com");
    }

    // Disposal is not necessary for AsyncSingleton unless the type used is IDisposable/IAsyncDisposable
    public ValueTask DisposeAsync()
    {
        GC.SuppressFinalize(this);

        return _client.DisposeAsync();
    }

    public void Dispose()
    {
        GC.SuppressFinalize(this);
        
        _client.Dispose();
    }
}