YieldAwaitable.cs

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//
// YieldAwaitable.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

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

namespace System.Runtime.CompilerServices
{
    public struct YieldAwaitable
    {
        public struct YieldAwaiter : ICriticalNotifyCompletion
        {
            public bool IsCompleted {
                get {
                    return false;
                }
            }

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

                if (TaskScheduler.Current == TaskScheduler.Default) {
                    //
                    // Pass continuation as an argument to avoid allocating
                    // hoisting class
                    //
                    ThreadPool.QueueUserWorkItem (l => ((Action) l) (), continuation);
                } else {
                    new Task (continuation).Start (TaskScheduler.Current);
                }
            }
            
            public void UnsafeOnCompleted (Action continuation)
            {
                if (continuation == null)
                    throw new ArgumentNullException ("continuation");

                if (TaskScheduler.Current == TaskScheduler.Default) {
                    //
                    // Pass the continuation as an argument to avoid allocating
                    // hoisting class
                    //
                    //ThreadPool.UnsafeQueueUserWorkItem (l => ((Action) l) (), continuation);
                    ThreadPool.QueueUserWorkItem (l => ((Action) l) (), continuation);
                } else {
                    new Task (continuation).Start (TaskScheduler.Current);
                }
            }

            public void GetResult ()
            {
            }
        }

        public YieldAwaitable.YieldAwaiter GetAwaiter ()
        {
            return new YieldAwaiter ();
        }
    }
}

#endif