AlwaysAsyncAwaiter - http://stackoverflow.com/questions/32412426/unexpected-stack-overflow-despite-yielding

TaskExt.cs

// http://stackoverflow.com/questions/32412426/unexpected-stack-overflow-despite-yielding

public static class TaskExt
{
	public static AlwaysAsyncAwaiter<T> AlwaysAsync<T>(this Task<T> @this) { return new AlwaysAsyncAwaiter<T>(@this); }

	public struct AlwaysAsyncAwaiter<T> : System.Runtime.CompilerServices.ICriticalNotifyCompletion
	{
		readonly Task<T> _task;

		public AlwaysAsyncAwaiter(Task<T> task)
		{
			_task = task;
		}

		public AlwaysAsyncAwaiter<T> GetAwaiter() { return this; }

		public bool IsCompleted { get { return false; } }

		public T GetResult() { return _task.GetAwaiter().GetResult(); }

		public void UnsafeOnCompleted(Action continuation)
		{
			// optimization (it has a race condition which we address below)
			if (_task.IsCompleted)
			{
				ThreadPool.UnsafeQueueUserWorkItem(_ => continuation(), null);
				return;
			}

			// task can still get completed before ContinueWith returns
			var locker = new Object();
			lock (locker)
			{
				var executedSynchronously = true;
				try
				{
					using (ExecutionContext.SuppressFlow())
					{
						_task.ContinueWith(
							_ =>
							{
								lock (locker)
								{
									if (executedSynchronously)
									{
										ThreadPool.UnsafeQueueUserWorkItem(__ => continuation(), null);
										return;
									}
								}
								continuation();
							},
							CancellationToken.None,
							TaskContinuationOptions.ExecuteSynchronously,
							TaskScheduler.Default);
					}
				}
				finally
				{
					executedSynchronously = false;
				}
			}

			//// simulate a race condition
			//Thread.Sleep(100);
			//Console.WriteLine(new { where = "inside", Environment.CurrentManagedThreadId });
		}

		public void OnCompleted(Action continuation)
		{
			throw new NotImplementedException();
		}
	}
}