TaskToApm.cs

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using System.Diagnostics.CodeAnalysis;
 
namespace System.Threading.Tasks;
 
internal static class TaskToApm
{
    internal sealed class TaskAsyncResult : IAsyncResult
    {
        internal readonly Task _task;
 
        private readonly AsyncCallback _callback;
 
        public object AsyncState { get; }
 
        public bool CompletedSynchronously { get; }
 
        public bool IsCompleted => _task.IsCompleted;
 
        public WaitHandle AsyncWaitHandle => ((IAsyncResult)_task).AsyncWaitHandle;
 
        internal TaskAsyncResult(Task task, object state, AsyncCallback callback)
        {
            _task = task;
            AsyncState = state;
            if (task.IsCompleted)
            {
                CompletedSynchronously = true;
                callback?.Invoke(this);
            }
            else if (callback != null)
            {
                _callback = callback;
                _task.ConfigureAwait(continueOnCapturedContext: false).GetAwaiter().OnCompleted(InvokeCallback);
            }
        }
 
        private void InvokeCallback()
        {
            _callback(this);
        }
    }
 
    public static IAsyncResult Begin(Task task, AsyncCallback callback, object state)
    {
        return new TaskAsyncResult(task, state, callback);
    }
 
    public static TResult End<TResult>(IAsyncResult asyncResult)
    {
        if (GetTask(asyncResult) is Task<TResult> task)
        {
            return task.GetAwaiter().GetResult();
        }
        ThrowArgumentException(asyncResult);
        return default(TResult);
    }
 
    public static Task GetTask(IAsyncResult asyncResult)
    {
        return (asyncResult as TaskAsyncResult)?._task;
    }
 
    [DoesNotReturn]
    private static void ThrowArgumentException(IAsyncResult asyncResult)
    {
        throw (asyncResult == null) ? new ArgumentNullException("asyncResult") : new ArgumentException(null, "asyncResult");
    }
}