VB.Net Dispose /垃圾收集器不釋放資源？

Question

使用VS 2015年在這裏......只是做了一個小測試程序，以比較異步之間的性能差異的WebRequest使用任務和方式，我用HttpWebRequest.BeginGetResponse

之前這樣做，但關鍵是我想處置通過實現IDispoable用於異步請求的狀態對象的狀態，但在診斷中顯示分配的RAM大小保持不變？我的印象是調用dispose會釋放對象正在使用的資源？這裏是我使用的代碼，我也嘗試將對象設置爲Nothing。

Imports System.Net 

Public Class Form1 
    Private sw As New Stopwatch 

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click 
     Dim req As HttpWebRequest = HttpWebRequest.Create("http://example.com") 
     Dim state As New RequestState 
     state.req = req 
     req.BeginGetResponse(AddressOf respCallback, state) 
    End Sub 

    Private Sub respCallback(ar As IAsyncResult) 
     Dim state As RequestState = ar.AsyncState 
     state.resp = state.req.EndGetResponse(ar) 
     state.respStream = state.resp.GetResponseStream 
     state.respStream.BeginRead(state.buffer, 0, 1024, AddressOf readCallback, state) 
    End Sub 

    Private Sub readCallback(ar As IAsyncResult) 
     Dim state As RequestState = ar.AsyncState 
     Dim read As Integer = state.respStream.EndRead(ar) 
     If read > 0 Then 
      state.respBody += System.Text.ASCIIEncoding.ASCII.GetString(state.buffer, 0, read) 
      state.respStream.BeginRead(state.buffer, 0, 1024, AddressOf readCallback, state) 
     Else 
      state.respStream.Close() 
      MsgBox(state.respBody) 
      state.Dispose() 
     End If 
    End Sub 

Public Class RequestState 
    Implements IDisposable 

    Public req As HttpWebRequest 
    Public resp As HttpWebResponse 
    Public respStream As IO.Stream 
    Public buffer(1024) As Byte 
    Public respBody As String 

#Region "IDisposable Support" 
Protected Overridable Sub Dispose(disposing As Boolean) 
    If Not disposedValue Then 
     If disposing Then 
      ' TODO: dispose managed state (managed objects). 
      req = Nothing 
      resp.Close() 
      resp.Dispose() 
      resp = Nothing 
      respStream.Close() 
      respStream.Dispose() 
      respStream = Nothing 
      buffer = Nothing 
      respBody = Nothing 
     End If 

     ' TODO: free unmanaged resources (unmanaged objects) and override Finalize() below. 
     ' TODO: set large fields to null. 
    End If 
    disposedValue = True 
End Sub 

    ' TODO: override Finalize() only if Dispose(disposing As Boolean) above has code to free unmanaged resources. 
    'Protected Overrides Sub Finalize() 
    ' ' Do not change this code. Put cleanup code in Dispose(disposing As Boolean) above. 
    ' Dispose(False) 
    ' MyBase.Finalize() 
    'End Sub 

    ' This code added by Visual Basic to correctly implement the disposable pattern. 
    Public Sub Dispose() Implements IDisposable.Dispose 
     ' Do not change this code. Put cleanup code in Dispose(disposing As Boolean) above. 
     Dispose(True) 
     ' TODO: uncomment the following line if Finalize() is overridden above. 
     ' GC.SuppressFinalize(Me) 
    End Sub 
#End Region 
End Class 

Answer 1

簡單地實現IDisposable不自動釋放內存，所有這一切都是由程序員來釋放託管和非託管資源。

在Dispose(disposing As Boolean)方法，你將不得不呼籲每個變量落實處置功能Close()或Dispose()：

Protected Overridable Sub Dispose(disposing As Boolean) 
    If Not disposedValue Then 
     If disposing Then 
      'Here you dispose all managed resources. 
      respStream.Close() 
      respStream.Dispose() 
      resp.Close() 
     End If 
    End If 
    disposedValue = True 
End Sub 

當你與你的異步操作完成後，一定要關閉IAsyncResult.AsyncWaitHandle對象。你應該能夠做到這一點在每個回調方法的末尾：

ar.Close()