我们需要关闭 System.Net.WebRequest 的 ResponseStream 吗？
我想知道我最终会从这段代码中获得任何未关闭的流：
Public Function [Get](ByVal url As String) As String
Using reader = New System.IO.StreamReader(System.Net.WebRequest.Create(url).GetResponse.GetResponseStream)
Return reader.ReadToEnd
End Using
End Function
那怎么样：
Public Function Get2(ByVal url As String) As String
Using stream = System.Net.WebRequest.Create(url).GetResponse.GetResponseStream
Using reader = New System.IO.StreamReader(stream)
Return reader.ReadToEnd
End Using
End Using
End Function
基本上，我们需要关闭 System.Net.WebRequest 的 ResponseStream 吗？
I was wondering will I end up having any unclosed streams from this code:
Public Function [Get](ByVal url As String) As String
Using reader = New System.IO.StreamReader(System.Net.WebRequest.Create(url).GetResponse.GetResponseStream)
Return reader.ReadToEnd
End Using
End Function
What about this:
Public Function Get2(ByVal url As String) As String
Using stream = System.Net.WebRequest.Create(url).GetResponse.GetResponseStream
Using reader = New System.IO.StreamReader(stream)
Return reader.ReadToEnd
End Using
End Using
End Function
Basically, do we need to close the System.Net.WebRequest's ResponseStream ?
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您需要关闭响应流或者您需要关闭响应。请注意，关闭包装
Stream的 StreamReader 无论如何都会关闭流，因此第一个版本应该没问题。 （请注意，我认为“使用Using语句进行处置”在语义上等于“在finally块中关闭” - 显式调用Close而不是仅仅处置流或响应没有任何好处.)我相信关闭流就足够了 - 您也不需要关闭响应 - 事实上这就是 MSDN 的规定，但为了清楚起见，我个人会这样做：（
有一个理论 这样做的好处是，如果
GetResponse返回成功，但GetResponseStream或StreamReader构造函数抛出异常（我不知道），它将关闭响应。没想到会这样有任何实际影响。）如果您不关闭任何东西，您可能很容易在将来对同一主机的请求中遇到超时 - “打开”响应本质上将占用与该主机的连接，默认情况下，每个主机最多只能打开两个连接。这是超时的一个非常常见的原因——有很多这样的问题，人们因为没有关闭任何东西而超时。
You either need to close the response stream or you need to close the response. Note that closing a
StreamReaderwrapping aStreamwill close the stream anyway, so the first version should be okay. (Note that I'm deeming "dispose with a Using statement" to be semantically equal to "close in a finally block" - there's no benefit in explicitly callingCloseinstead of just disposing of the stream or response.)I believe that closing the stream is good enough - that you don't need to close the response as well - and indeed that's what MSDN states, but personally I'd do so for clarity:
(There's a theoretical benefit here that it will close the response if
GetResponsereturns successfully but eitherGetResponseStreamor theStreamReaderconstructor throws an exception. I don't expect that to have any practical implications.)If you don't close anything, you could very easily run into timeouts in future requests to the same host - the "open" response will essentially hog the connection to that host, and by default there's a limit of two open connections per host. This is a very common cause of timeouts - there are lots of SO questions where folks are getting timeouts due to not closing anything.
没有必要在 WebResponse 上调用 Close 方法，但这样做并没有什么害处
http://msdn.microsoft.com/en-us/library/debx8sh9.aspx
It is not necessary to call the Close method on the WebResponse, but doing so is not harmful
http://msdn.microsoft.com/en-us/library/debx8sh9.aspx