异步

await不会阻塞主线程(UI不会假死，IIS回收空闲线程)，会把后面的操作封装成callback

Result会阻塞线程

async/await（Task） //await后不会开启新的线程，只有async里用Task.Run或Task.Factory.Startnew开启新线程后，await时才会等待线程，不加await时异步执行, await只能等待Task

static void Main(string[] args)
{
    Console.WriteLine("Main Thread Id: {0}
", Thread.CurrentThread.ManagedThreadId);
    Test();
    Console.ReadLine();
}
 
static async Task Test()
{
    Console.WriteLine("Before calling GetName, Thread Id: {0}
", Thread.CurrentThread.ManagedThreadId);
    var name = GetName();   //我们这里没有用 await,所以下面的代码可以继续执行
    // 但是如果上面是 await GetName()，下面的代码就不会立即执行，输出结果就不一样了。
    Console.WriteLine("End calling GetName.
");
    Console.WriteLine("Get result from GetName: {0}", await name);
}
 
static async Task<string> GetName()
{
    // 这里还是主线程
    Console.WriteLine("Before calling Task.Run, current thread Id is: {0}", Thread.CurrentThread.ManagedThreadId);
    return await Task.Run(() =>
    {
        Thread.Sleep(1000);
        Console.WriteLine("'GetName' Thread Id: {0}", Thread.CurrentThread.ManagedThreadId);
        return "Jesse";
    });
}

HttpClient

client.GetAsync("http://google.com").Result

await client.GetAsync("http://google.com")

response.Content.ReadAsAsync().Result

await response.Content.ReadAsAsync()

Task<HttpResponseMessage> responseTask= httpClient.GetAsync(“http://en.wikipedia.org/”); //创建Task并执行

HttpResponseMessage response = await responseTask; //等待task执行完毕

//并发
        public async Task Await3Task()
        {
            var task3 = Delay3000Async();
            var task2 = Delay2000Async();
            var task1 = Delay1000Async();

            await task3;
            await task2;
            await task1;
        }

        //非并发
        public async Task Await3DelayAsync()
        {
            await Delay3000Async();
            await Delay2000Async();
            await Delay1000Async();
        }

        //并发，这里甚至可以把var task3等去掉，直接调用xxxAsync(),只是会出现警告的波浪罢了
        public void NoAwait3Task()
        {
            var task3 = Delay3000Async();
            var task2 = Delay2000Async();
            var task1 = Delay1000Async();
        }

　　

线程间通信
winform invode
wpf dispacher
asp.net SynchronizationContext(将任务(delegate)以队列的方式放入context中，再把context关联到
具体线程上，多个线程可关联相同的SynchronizationContext，SynchronizationContext.Current获取
当前线程关联的上下文)

url:http://www.cnblogs.com/jesse2013/p/Asynchronous-Programming-In-DotNet.html

url:http://www.cnblogs.com/richieyang/p/5020849.html