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using System.Threading.Channels; | |
var uberQueue = new UberQueue<string>(Enumerable | |
.Range(0, 10) | |
.Select(queueIndex => new RandomDelayQueue(queueIndex)) | |
.ToArray()); | |
var uberQueueConsumers = Enumerable | |
.Range(0, 3) | |
.Select(consumerIndex => Task.Run(async () => | |
{ | |
while (true) | |
{ | |
try | |
{ | |
var result = await uberQueue.DequeueAsync(); | |
Console.WriteLine($"consumer {consumerIndex}: {result}"); | |
} | |
catch (Exception ex) | |
{ | |
Console.WriteLine($"consumer {consumerIndex}: Catched: {ex.Message}"); | |
} | |
} | |
})) | |
.ToArray(); | |
await Task.WhenAll(uberQueueConsumers); | |
public class UberQueue<T> | |
{ | |
private readonly SemaphoreSlim _lock; | |
private readonly Task _deferFirstDequeueTask; | |
private readonly Channel<(IAsyncQueue<T> queue, Task<T> dequeueTask)> _channel; | |
public UberQueue(IAsyncQueue<T>[] queues) | |
{ | |
_channel = Channel.CreateBounded<(IAsyncQueue<T> queue, Task<T> dequeueTask)>(queues.Length); | |
_lock = new SemaphoreSlim(1, 1); | |
_deferFirstDequeueTask = new Task(() => | |
{ | |
foreach (var queue in queues) | |
Requeue(queue); | |
}); | |
} | |
public async Task<T> DequeueAsync() | |
{ | |
await EnsureFirstDequeueAsync().ConfigureAwait(false); | |
var (queue, dequeueTask) = await _channel.Reader.ReadAsync().ConfigureAwait(false); | |
Requeue(queue); | |
return await dequeueTask.ConfigureAwait(false); | |
} | |
private async Task EnsureFirstDequeueAsync() | |
{ | |
if (_deferFirstDequeueTask.Status == TaskStatus.Created) | |
{ | |
await _lock.WaitAsync().ConfigureAwait(false); | |
try | |
{ | |
if (_deferFirstDequeueTask.Status == TaskStatus.Created) | |
_deferFirstDequeueTask.Start(); | |
} | |
finally | |
{ | |
_lock.Release(); | |
} | |
} | |
await _deferFirstDequeueTask.ConfigureAwait(false); | |
} | |
private void Requeue(IAsyncQueue<T> queue) | |
{ | |
_ = queue | |
.DequeueAsync() | |
.ContinueWith(dequeueTask => _channel.Writer.WriteAsync((queue, dequeueTask)).ConfigureAwait(false), TaskContinuationOptions.ExecuteSynchronously) | |
.ConfigureAwait(false); | |
} | |
} | |
public interface IAsyncQueue<T> | |
{ | |
Task<T> DequeueAsync(); | |
} | |
public class RandomDelayQueue : IAsyncQueue<string> | |
{ | |
private readonly int _index; | |
private int _counter = 0; | |
public RandomDelayQueue(int index) | |
{ | |
_index = index; | |
} | |
public async Task<string> DequeueAsync() | |
{ | |
var count = _counter++; | |
var timeout = Random.Shared.Next(10, 100); | |
Console.WriteLine($"queue {_index}/{count} will finish in {timeout}ms"); | |
await Task.Delay(timeout).ConfigureAwait(false); | |
var result = $"queue {_index}/{count} finished after {timeout}ms"; | |
if (30 < timeout && timeout < 40) | |
throw new Exception(result); | |
return result; | |
} | |
} |
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https://twitter.com/davidfowl/status/1426453915357175819