[转][C#]降级.net 源码4.5

来自：https://www.cnblogs.com/had37210/p/8057042.html

主要是 Task 的降级：

     1.net4.5.2 引入了 async/await 关键字. 这个其实国外大神已经有源码放出来了,我们把代码直接引入cefsharp 这个工程. 就可以直接在4.0里使用 async/await;

     2.net4.5 对task api 做了扩展, 我们只需要在.net4.0实现一下对应的api.就可以了.

    3. 源码里面用了很多4.5才有的GetTypeInfo      扩展方法错误. 它返回的类型是typeinfo,不用管它,把GetTypeInfo      删掉. 直接Type  调用就可以了.

    4. 对Task静态方法的扩展,需要修改一下,静态方法的调用方式.

以上是要点.下面贴源码:

本段源码是对:async/await的支持:

namespace System.Threading.Tasks
{
    public static class TaskEx
    {
        public static TaskAwaiter GetAwaiter(this Task task)
        {
            return new TaskAwaiter(task);
        }

        public static TaskAwaiter<T> GetAwaiter<T>(this Task<T> task)
        {
            return new TaskAwaiter<T>(task);
        }
    }

    public struct TaskAwaiter : INotifyCompletion
    {
        readonly Task task;

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

        internal static TaskScheduler TaskScheduler
        {
            get
            {
                if (SynchronizationContext.Current == null)
                    return TaskScheduler.Default;
                else
                    return TaskScheduler.FromCurrentSynchronizationContext();
            }
        }

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

        public void OnCompleted(Action continuation)
        {
            this.task.ContinueWith(
                delegate (Task task) {
                    continuation();
                }, TaskAwaiter.TaskScheduler);
        }

        public void GetResult()
        {
            try
            {
                task.Wait();
            }
            catch (AggregateException ex)
            {
                throw ex.InnerExceptions[0];
            }
        }
    }

    public struct TaskAwaiter<T> : INotifyCompletion
    {
        readonly Task<T> task;

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

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

        public void OnCompleted(Action continuation)
        {
            this.task.ContinueWith(
                delegate (Task<T> task) {
                    continuation();
                }, TaskAwaiter.TaskScheduler);
        }

        public T GetResult()
        {
            try
            {
                return task.Result;
            }
            catch (AggregateException ex)
            {
                throw ex.InnerExceptions[0];
            }
        }
    }
}

namespace System.Runtime.CompilerServices
{
    public interface INotifyCompletion
    {
        void OnCompleted(Action continuation);
    }

    public interface ICriticalNotifyCompletion : INotifyCompletion
    {
        [SecurityCritical]
        void UnsafeOnCompleted(Action continuation);
    }

    public interface IAsyncStateMachine
    {
        void MoveNext();
        void SetStateMachine(IAsyncStateMachine stateMachine);
    }

    public struct AsyncVoidMethodBuilder
    {
        public static AsyncVoidMethodBuilder Create()
        {
            return new AsyncVoidMethodBuilder();
        }

        public void SetException(Exception exception)
        {
            throw exception;
        }

        public void SetResult()
        {
        }

        public void SetStateMachine(IAsyncStateMachine stateMachine)
        {
            // Should not get called as we don't implement the optimization that this method is used for.
            throw new NotImplementedException();
        }

        public void Start<TStateMachine>(ref TStateMachine stateMachine) where TStateMachine : IAsyncStateMachine
        {
            stateMachine.MoveNext();
        }

        public void AwaitOnCompleted<TAwaiter, TStateMachine>(ref TAwaiter awaiter, ref TStateMachine stateMachine) where TAwaiter : INotifyCompletion where TStateMachine : IAsyncStateMachine
        {
            awaiter.OnCompleted(stateMachine.MoveNext);
        }

        public void AwaitUnsafeOnCompleted<TAwaiter, TStateMachine>(ref TAwaiter awaiter, ref TStateMachine stateMachine) where TAwaiter : ICriticalNotifyCompletion where TStateMachine : IAsyncStateMachine
        {
            awaiter.OnCompleted(stateMachine.MoveNext);
        }
    }

    public struct AsyncTaskMethodBuilder
    {
        TaskCompletionSource<object> tcs;

        public Task Task { get { return tcs.Task; } }

        public static AsyncTaskMethodBuilder Create()
        {
            AsyncTaskMethodBuilder b;
            b.tcs = new TaskCompletionSource<object>();
            return b;
        }

        public void Start<TStateMachine>(ref TStateMachine stateMachine) where TStateMachine : IAsyncStateMachine
        {
            stateMachine.MoveNext();
        }

        public void SetStateMachine(IAsyncStateMachine stateMachine)
        {
            // Should not get called as we don't implement the optimization that this method is used for.
            throw new NotImplementedException();
        }

        public void AwaitOnCompleted<TAwaiter, TStateMachine>(ref TAwaiter awaiter, ref TStateMachine stateMachine) where TAwaiter : INotifyCompletion where TStateMachine : IAsyncStateMachine
        {
            awaiter.OnCompleted(stateMachine.MoveNext);
        }

        public void AwaitUnsafeOnCompleted<TAwaiter, TStateMachine>(ref TAwaiter awaiter, ref TStateMachine stateMachine) where TAwaiter : ICriticalNotifyCompletion where TStateMachine : IAsyncStateMachine
        {
            awaiter.OnCompleted(stateMachine.MoveNext);
        }

        public void SetResult()
        {
            tcs.SetResult(null);
        }

        public void SetException(Exception exception)
        {
            tcs.SetException(exception);
        }
    }

    public struct AsyncTaskMethodBuilder<T>
    {
        TaskCompletionSource<T> tcs;

        public Task<T> Task { get { return tcs.Task; } }

        public static AsyncTaskMethodBuilder<T> Create()
        {
            AsyncTaskMethodBuilder<T> b;
            b.tcs = new TaskCompletionSource<T>();
            return b;
        }

        public void Start<TStateMachine>(ref TStateMachine stateMachine) where TStateMachine : IAsyncStateMachine
        {
            stateMachine.MoveNext();
        }

        public void SetStateMachine(IAsyncStateMachine stateMachine)
        {
            // Should not get called as we don't implement the optimization that this method is used for.
            throw new NotImplementedException();
        }

        public void AwaitOnCompleted<TAwaiter, TStateMachine>(ref TAwaiter awaiter, ref TStateMachine stateMachine) where TAwaiter : INotifyCompletion where TStateMachine : IAsyncStateMachine
        {
            awaiter.OnCompleted(stateMachine.MoveNext);
        }

        public void AwaitUnsafeOnCompleted<TAwaiter, TStateMachine>(ref TAwaiter awaiter, ref TStateMachine stateMachine) where TAwaiter : ICriticalNotifyCompletion where TStateMachine : IAsyncStateMachine
        {
            AwaitOnCompleted(ref awaiter, ref stateMachine);
        }

        public void SetResult(T result)
        {
            tcs.SetResult(result);
        }

        public void SetException(Exception exception)
        {
            tcs.SetException(exception);
        }
    }
}

这段是对 Task 的扩展

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace CefSharp
{
   public class TaskEx
    {
        public static Task<T> FromResult<T>(T t)
        {
            return Task.Factory.StartNew<T>(() => t);
        }
        public static Task Run(Action action)
        {
            var tcs = new TaskCompletionSource<object>();
            new Thread(() => {
                    try
                    {
                        action();
                        tcs.SetResult(null);
                    }
                    catch (Exception ex)
                    {
                        tcs.SetException(ex);
                    }
                })
                { IsBackground = true }.Start();
            return tcs.Task;
        }
        public static Task<TResult> Run<TResult>(Func<TResult> function)
        {
            var tcs = new TaskCompletionSource<TResult>();
            new Thread(() =>
                {
                    try
                    {
                        tcs.SetResult(function());
                    }
                    catch (Exception ex)
                    {
                        tcs.SetException(ex);
                    }
                })
                { IsBackground = true }.Start();
            return tcs.Task;
        }
        public static Task Delay(int milliseconds)
        {
            var tcs = new TaskCompletionSource<object>();
            var timer = new System.Timers.Timer(milliseconds) { AutoReset = false };
            timer.Elapsed += delegate { timer.Dispose(); tcs.SetResult(null); };
            timer.Start();
            return tcs.Task;
        }
    }
}

把这些添加到代码里, 遇到 Task.Run 的时候,替换成 TaskEx.Run,遇到 Task.Delay 替换为TaskEx.Delay.

还有报 GetTypeInfo 这个错误的地方，删除就Ok了。