A thread-safe asynchronous queue.

AsyncQueue.cs

using System.Threading.Tasks.Dataflow;

namespace AsyncQueue;

/// <summary>
/// A thread-safe asynchronous queue.
/// </summary>
/// <example>
/// <code>
/// var queue = new AsyncQueue`int();
/// await foreach(int i in queue) {
///     // Writes a line as soon as some other Task calls queue.Enqueue(..)
///     Console.WriteLine(i);
/// }
/// </code>
/// </example>
/// <remarks>
/// Inspired by an amazing answer on StackOverflow [here](https://stackoverflow.com/a/55912725/14860947)
/// </remarks>
/// <typeparam name="T">
/// The type of the elements in the queue.
/// </typeparam>
public sealed class AsyncQueue<T> : IAsyncEnumerable<T>
{
    private readonly SemaphoreSlim _enumerationSemaphore = new(1);
    private readonly BufferBlock<T> _bufferBlock = new();

    /// <summary>
    /// Add an item to the queue atomically.
    /// </summary>
    /// <param name="item">The item to add</param>
    public void Enqueue(T item) => _bufferBlock.Post(item);

    public async IAsyncEnumerator<T> GetAsyncEnumerator(CancellationToken ct = default)
    {
        await _enumerationSemaphore.WaitAsync(ct);

        while (!ct.IsCancellationRequested)
            yield return await _bufferBlock.ReceiveAsync(ct);

        _enumerationSemaphore.Release();
    }
}