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快速总结：VS 2010 VB.NET 中的应用程序，当前在 Win 2008 服务器上运行以进行测试。它是一个多线程（8 个线程）应用程序，从 .NET 套接字读取数据。

细节：

Public Class StateObject
    Public workSocket As Socket = Nothing ' Client socket.
    Public BufferSize As Integer = 20000    ' Size of receive buffer.   Orig: 20000
    Public buffer(20000) As Byte            ' Receive buffer.           Orig: (20000)
    Public sb As New StringBuilder()      ' Received data string.
End Class 'StateObject

Private Sub Read_Callback(ar As IAsyncResult)

    Dim state As StateObject = CType(ar.AsyncState, StateObject)
    Dim bytesRead As Long = 0
    Dim client As Socket = state.workSocket

    SyncLock state

    Try
    ' Read data from the remote device.
    bytesRead = client.EndReceive(ar)

    If bytesRead > 0 Then ' There might be more data, so store the data received so far.

    SyncLock state.sb
    **state.sb.Append(Encoding.Default.GetString(state.buffer, 0, bytesRead))**
    End SyncLock

    If state.sb.Length > 1 Then
    SyncLock state.sb
    response = state.sb.ToString()
    **state.sb.Clear()**

    End SyncLock
    End If


    client.BeginReceive(state.buffer, 0, state.BufferSize, 0, _
    AddressOf Read_Callback, state)
    Else ' All the data has arrived; put it in response.

    If state.sb.Length > 1 Then
    SyncLock state.sb
    response = state.sb.ToString()
    state.sb.Clear()

    End SyncLock

    End If

    readDone.Set()
    End If
    Catch e As Exception
    AppEventLog.WriteEntry("SocketManager.Read_Callback: (LineNum=" & Err.Erl.ToString & ") " & e.Message & vbCrLf & _
    "bytesRead = " & bytesRead.ToString & vbCrLf & _
    "state.sb.Length = " & state.sb.Length.ToString & vbCrLf & _
    "state.sb.Capacity = " & state.sb.Capacity.ToString & vbCrLf & _
    "state.sb.MaxCapacity = " & state.sb.MaxCapacity.ToString & vbCrLf & _
    "state.workSocket.Available = " & state.workSocket.Available.ToString(), EventLogEntryType.Error)
    End Try
    End SyncLock

    state = Nothing

End Sub 'Read_Callback

这是 Windows 事件视图中的错误日志：

SocketManager.Read_Callback: (LineNum=80) Exception of type 'System.OutOfMemoryException' was thrown.
bytesRead = 20000
state.sb.Length = 0
state.sb.Capacity = 20000
state.sb.MaxCapacity = 2147483647
state.workSocket.Available = 0


**LineNum = 80 causes most errors but sometime occurs at LineNum = 130** (see highlighted lines above)

问题：

  1. 这是由 StringBuilder 引起的还是其他原因？
  2. 解决办法是什么？
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