TaskAwaiter.cs

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//
// TaskAwaiter.cs
//
// Authors:
//  Marek Safar  <marek.safar@gmail.com>
//
// Copyright (C) 2011 Novell, Inc (http://www.novell.com)
// Copyright (C) 2011 Xamarin, Inc (http://www.xamarin.com)
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

#if NET_4_5 || UNITY_5_3_OR_NEWER

using System.Threading;
using System.Threading.Tasks;

namespace System.Runtime.CompilerServices
{
    public struct TaskAwaiter : ICriticalNotifyCompletion
    {
        readonly Task task;

        internal TaskAwaiter (Task task)
        {
            this.task = task;
        }

        public bool IsCompleted {
            get {
                return task.IsCompleted;
            }
        }

        public void GetResult ()
        {
            if (task.Status != TaskStatus.RanToCompletion)
                throw HandleUnexpectedTaskResult (task);
        }

        internal static Exception HandleUnexpectedTaskResult (Task task)
        {
            switch (task.Status) {
            case TaskStatus.Canceled:
                return new TaskCanceledException (task);
            case TaskStatus.Faulted:
                return task.Exception.InnerException;
            default:
                return new InvalidOperationException ("The task has not finished yet");
            }
        }

        internal static void HandleOnCompleted (Task task, Action continuation, bool continueOnSourceContext, bool manageContext)
        {
            if (continueOnSourceContext && SynchronizationContext.Current != null) {
                task.ContinueWith (new SynchronizationContextContinuation (continuation, SynchronizationContext.Current));
            } else {
                task.ContinueWith (new ActionContinuation (continuation));
            }
        }

        public void OnCompleted (Action continuation)
        {
            if (continuation == null)
                throw new ArgumentNullException ("continuation");

            HandleOnCompleted (task, continuation, true, true);
        }
        
        public void UnsafeOnCompleted (Action continuation)
        {
            if (continuation == null)
                throw new ArgumentNullException ("continuation");

            HandleOnCompleted (task, continuation, true, false);
        }
    }
}

#endif