RendezvousAwaitable.cs

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using System.Runtime.CompilerServices;
using System.Runtime.ExceptionServices;
 
namespace System.Threading.Tasks;
 
internal class RendezvousAwaitable<TResult> : ICriticalNotifyCompletion, INotifyCompletion
{
    private static readonly Action s_completionSentinel = delegate
    {
    };
 
    private Action _continuation;
 
    private ExceptionDispatchInfo _error;
 
    private TResult _result;
 
    public bool RunContinuationsAsynchronously { get; set; } = true;
 
 
    public bool IsCompleted
    {
        get
        {
            Action action = Volatile.Read(ref _continuation);
            return action != null;
        }
    }
 
    public RendezvousAwaitable<TResult> GetAwaiter()
    {
        return this;
    }
 
    public TResult GetResult()
    {
        _continuation = null;
        ExceptionDispatchInfo error = _error;
        if (error != null)
        {
            _error = null;
            error.Throw();
        }
        TResult result = _result;
        _result = default(TResult);
        return result;
    }
 
    public void SetResult(TResult result)
    {
        _result = result;
        NotifyAwaiter();
    }
 
    private void NotifyAwaiter()
    {
        Action action = _continuation ?? Interlocked.CompareExchange(ref _continuation, s_completionSentinel, null);
        if (action != null)
        {
            if (RunContinuationsAsynchronously)
            {
                Task.Run(action);
            }
            else
            {
                action();
            }
        }
    }
 
    public void OnCompleted(Action continuation)
    {
        Action action = _continuation ?? Interlocked.CompareExchange(ref _continuation, continuation, null);
        if (action != null)
        {
            Task.Run(continuation);
        }
    }
 
    public void UnsafeOnCompleted(Action continuation)
    {
        OnCompleted(continuation);
    }
}