await using and IAsyncDisposable

Context: IAsyncDisposable is the asynchronous counterpart of IDisposable. It defines DisposeAsync() which returns ValueTask. The await using statement (C# 8.0+) allows you to asynchronously dispose of resources, which is useful for classes that perform asynchronous cleanup (e.g., closing network streams, flushing file buffers).

Usage Example

using System;
using System.IO;
using System.Threading.Tasks;

public class AsyncResource : IAsyncDisposable
{
    private FileStream _stream;

    public AsyncResource(string path)
    {
        _stream = new FileStream(path, FileMode.OpenOrCreate);
    }

    public async ValueTask DisposeAsync()
    {
        if (_stream != null)
        {
            await _stream.FlushAsync();
            await _stream.DisposeAsync();
        }
        GC.SuppressFinalize(this);
    }

    // Optional finalizer if needed
    ~AsyncResource() { }
}

public class AsyncUsingDemo
{
    public static async Task UseAsyncResourceAsync()
    {
        await using (var resource = new AsyncResource("test.txt"))
        {
            // Use resource
        } // DisposeAsync() is awaited here
    }
}

Output console

// No output; the async disposal happens in the background.

Important notes

• await using requires the resource to implement IAsyncDisposable.
• If both IDisposable and IAsyncDisposable are implemented, the compiler prefers await using for asynchronous disposal.

Real‑world usage example

Network stream reader – HttpResponseMessage implements IAsyncDisposable. Using await using ensures that the response stream is asynchronously disposed, releasing the connection back to the pool.
See .NET docs on IAsyncDisposable.

Related sections

• 10.2.3 using statement
• 10.2 IDisposable