所以我试图让我的头脑围绕这个新的“异步”东西在.net 4.5.我以前玩异步控制器和任务并行库,并清理了这段代码：
采取这种模式：
public class TestOutput
{
public string One { get; set; }
public string Two { get; set; }
public string Three { get; set; }
public static string DoWork(string input)
{
Thread.Sleep(2000);
return input;
}
}
在这样的控制器中使用哪一个：
public void IndexAsync()
{
AsyncManager.OutstandingOperations.Increment(3);
Task.Factory.StartNew(() =>
{
return TestOutput.DoWork("1");
})
.ContinueWith(t =>
{
AsyncManager.OutstandingOperations.Decrement();
AsyncManager.Parameters["one"] = t.Result;
});
Task.Factory.StartNew(() =>
{
return TestOutput.DoWork("2");
})
.ContinueWith(t =>
{
AsyncManager.OutstandingOperations.Decrement();
AsyncManager.Parameters["two"] = t.Result;
});
Task.Factory.StartNew(() =>
{
return TestOutput.DoWork("3");
})
.ContinueWith(t =>
{
AsyncManager.OutstandingOperations.Decrement();
AsyncManager.Parameters["three"] = t.Result;
});
}
public ActionResult IndexCompleted(string one,string two,string three)
{
return View(new TestOutput { One = one,Two = two,Three = three });
}
由于TPL的魔力,该控制器会在2秒内呈现视图.
现在,我预计(相当天真地),上面的代码将转换为以下内容,使用C#5的新“异步”和“等待”功能：
public async Task<ActionResult> Index()
{
return View(new TestOutput
{
One = await Task.Run(() =>TestOutput.DoWork("one")),Two = await Task.Run(() =>TestOutput.DoWork("two")),Three = await Task.Run(() =>TestOutput.DoWork("three"))
});
}
该控制器在6秒内呈现视图.在翻译的某个地方,代码变得不再平行.我知道异步和并行是两个不同的概念,但不知何故我认为代码将工作相同.有人可以指出这里发生了什么,如何解决？
解决方法
Somewhere in the translation the code became no longer parallel.
恰恰.等待(异步)等待单个操作完成.
并行异步操作可以通过启动实际的任务来完成,但不等待它们直到以后：
public async Task<ActionResult> Index()
{
// Start all three operations.
var tasks = new[]
{
Task.Run(() =>TestOutput.DoWork("one")),Task.Run(() =>TestOutput.DoWork("two")),Task.Run(() =>TestOutput.DoWork("three"))
};
// Asynchronously wait for them all to complete.
var results = await Task.WhenAll(tasks);
// Retrieve the results.
return View(new TestOutput
{
One = results[0],Two = results[1],Three = results[2]
});
}
附：还有一个Task.WhenAny.
