我注意到 CallContext.LogicalSetData / LogicalGetData 不工作,我希望他们做的方式。内部的
设置的值异步
方法被恢复的即使没有不同步或任何形式的线程切换,任何。
I noticed that CallContext.LogicalSetData/LogicalGetData
don't work the way I expected them to do. A value set inside an async
method gets restored even when there is no asynchrony or any kind of thread switching, whatsoever.
下面是一个简单的例子:
Here is a simple example:
using System;
using System.Runtime.Remoting.Messaging;
using System.Threading;
using System.Threading.Tasks;
namespace ConsoleApplication
{
class Program
{
static async Task<int> TestAsync()
{
CallContext.LogicalSetData("valueX", "dataX");
// commented out on purpose
// await Task.FromResult(0);
Console.WriteLine(CallContext.LogicalGetData("valueX"));
return 42;
}
static void Main(string[] args)
{
using(ExecutionContext.SuppressFlow())
{
CallContext.LogicalSetData("valueX", "dataXX");
Console.WriteLine(CallContext.LogicalGetData("valueX"));
Console.WriteLine(TestAsync().Result);
Console.WriteLine(CallContext.LogicalGetData("valueX"));
}
}
}
}
它产生这样的输出:
It produces this output:
dataXX
dataX
42
dataXX
如果我让 TestAsync
非异步,它按预期工作:
If I make TestAsync
non-async, it works as expected:
static Task<int> TestAsync()
{
CallContext.LogicalSetData("valueX", "dataX");
Console.WriteLine(CallContext.LogicalGetData("valueX"));
return Task.FromResult(42);
}
输出:
dataXX
dataX
42
dataX
我能够理解这种行为,如果我有在 TestAsync
一些真正的不同步,但这不是这里的情况。我甚至用 ExecutionContext.Sup pressFlow
,但是这并不能改变什么。
I would understand this behavior if I had some real asynchrony inside TestAsync
, but that's not the case here. I even use ExecutionContext.SuppressFlow
, but that doesn't change anything.
可能有人请解释为什么是这样工作的?
Could someone please explain why it works this way?
在这种情况下,正如预期的那样对于不同的人不同。 :)
"As expected" in this case is different for different people. :)
在原来的异步CTP(没有修改任何框架code),有一个异步本地之类的背景下,在所有的不支持。 MS修改 LocalCallContext
在.NET 4.5中添加这种支持。旧的行为(具有共享逻辑上下文)是特别是异步并发(即 Task.WhenAll
)。
In the original Async CTP (which did not modify any framework code), there was no support for an "async-local" kind of context at all. MS modified the LocalCallContext
in .NET 4.5 to add this support. The old behavior (with a shared logical context) is especially problematic when working with asynchronous concurrency (i.e., Task.WhenAll
).
我解释href="http://blog.stephencleary.com/2013/04/implicit-async-context-asynclocal.html" rel="nofollow">