URL监视器不断增加内存使用量

Question

我已经使用.net 4.0编写了vb中的URL监视程序。基本上它设置一个计时器使用htpwebreques/httpwebresponse每60分钟检查一次URL，并在URL关闭时发送电子邮件。但是，每次检查url时，应用程序使用的内存都会不断增加。这显然最终会导致一个问题，因为该应用程序旨在永久监控网站的可用性，并且监控机器最终将耗尽资源。

下面是我的CheckURL例程的代码。任何建议非常感谢，提前感谢。

Private Sub checkURL() 
    Timer1.Stop() 
    Dim wReq As HttpWebRequest 
    Dim wResp As HttpWebResponse ' WebResponse 

    wReq = HttpWebRequest.Create(url) 
    wReq.Method = "HEAD" 
    Try 
     wResp = wReq.GetResponse() 
     If wResp.StatusCode = 200 Then 
       txtResponse.Text = wResp.StatusCode & ": " & wResp.StatusDescription & vbNewLine & "The " & siteName & " is up" 

       'Only send success results if specified 
       If sendOnFailure = False Then 
        sendResults = True 
       End If 
      Else txtResponse.Text = "There may be a problem with the " & siteName & vbNewLine & "Please verify manually that it is operational." & vbNewLine & "The response received was:" & vbNewLine & "Status Code: " & wResp.StatusCode & " - " & wResp.StatusDescription 
       sendResults = True 
      End If 

     wResp.Close() 
     wResp = Nothing 
     wReq = Nothing 

    Catch ex As Exception 
      txtResponse.Text = "There may be a problem with the " & siteName & vbNewLine & "The error returned was:" & vbNewLine & ex.ToString 
      sendResults = True 

    End Try 

    txtLastCheck.Text = Now.ToString("d MMM yyyy HH:mm") 
    setNextCheck() 

End Sub 

Answer 1

首先，你应该使用Option Strict On，它会告诉你，你有变量的类型不匹配，甚至可能会建议更正你，例如，看到那里的DirectCast运营商在下面的代码中使用。

其次，HttpWebResponse有.Dispose()方法，所以你应该调用使用，当你完成它，或者像Zaggler指出的那样，你可以使用Using，以确保非托管资源被正确地清理，从而消除了内存泄漏你很关心。请注意，代码中可能存在其他类似问题，我们无法看到。

你应该不是设置为Nothing试图摆脱它们 - 这样做与垃圾收集器混乱，并没有做任何事情，以确保其清洁处置。

Option Strict On 
' .... 

Private Sub checkURL() 
    timer1.Stop() 
    Dim wReq As HttpWebRequest = DirectCast(HttpWebRequest.Create(url), HttpWebRequest) 
    wReq.Method = "HEAD" 

    Try 
     Using wResp As HttpWebResponse = DirectCast(wReq.GetResponse(), HttpWebResponse) 

      If wResp.StatusCode = 200 Then 
       txtResponse.Text = wResp.StatusCode & ": " & wResp.StatusDescription & vbNewLine & "The " & siteName & " is up" 

       'Only send success results if specified 
       If sendOnFailure = False Then 
        sendResults = True 
       End If 
      Else txtResponse.Text = "There may be a problem with the " & siteName & vbNewLine & "Please verify manually that it is operational." & vbNewLine & "The response received was:" & vbNewLine & "Status Code: " & wResp.StatusCode & " - " & wResp.StatusDescription 
       sendResults = True 
      End If 

      wResp.Close() 
     End Using 

    Catch ex As Exception 
     txtResponse.Text = "There may be a problem with the " & siteName & vbNewLine & "The error returned was:" & vbNewLine & ex.ToString 
     sendResults = True 

    End Try 

    txtLastCheck.Text = Now.ToString("d MMM yyyy HH:mm") 
    setNextCheck() 

End Sub