Object Pooling of VB Object
今天跟同时一起确认了一下这个问题.稍微总结一下.
问题:
vb写的一个com,实现了COM+的IObjectControl 或者 ObjectControl,这个跟.net 的enterprise Service 一样. 以为这样可以实现对象池,跟数据库连接池一样.避免每次都创建对象.所以一般都会实现这几个方法
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Private Sub ObjectControl_Activate()
End Sub
Private Function ObjectControl_CanBePooled() As Boolean
ObjectControl_CanBePooled = true
End Function
Private Sub ObjectControl_Deactivate()
End Sub
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然后我就想当然的以为这个跟vc或者.net 的实现方式一样. 假定如下:1.组件放到com+中,一定可以设置pool的大小,包括最小池,最大池. 2.如果我设定一个合适的池, 对象多次创建的情况下,应该有部分对象不需要实例化.
然后测试了一下,发现这两点更本就不对. 最后发现vb根本就不支持object pool. 微软的文档原文:object pooling is not possible for components created by vb6.
接下来的问题就是:
既然vb6 不支持object pooling ,那还为什么要实现objectcontrol 这个接口? 而我们的代码也一般都实现了这个接口.
这个问题的回答,我选择了一个com模板被asp调用的例子,并带有解释.
也就是说 对象每一次创建,都会顺序调用构造函数, Activate, 相反,释放的时候也会调用 Deactivate, terminate.
对于activate , 这调用该方法的时候可以活动对象所处的上下文, deactivate 释放该上下文的引用.如果你的com+组件中根本就不访问objectcontext 的话,则不需要该接口.
一般的template 如下:
Option Explicit
'---------------------------------------------------------------------------
-----
' Declarations
'---------------------------------------------------------------------------
-----
'* Interfaces
Implements COMSVCSLib.ObjectControl
'* Module level variables
Private m_objContext As COMSVCSLib.ObjectContext
Private m_blnMTS As Boolean
Private Const m_ModuleName As String = "nameOfClasshere" 'Used for
error handling
Private m_strUserName As String
Private m_strPassword As String
'---------------------------------------------------------------------------
-----
' Properties
'---------------------------------------------------------------------------
-----
'---------------------------------------------------------------------------
-----
' Methods
'---------------------------------------------------------------------------
-----
'---------------------------------------------------------------------------
-----
' MTS/COM+ Methods
'---------------------------------------------------------------------------
-----
Private Sub ObjectControl_Activate()
'******************************************************************
'* ObjectControl_Activate
'* ----------------------
'* One of the methods of the MTS/COM+ ObjectControl interface. This
subroutine
'* is used to set the objectContext and the MTS/COM+ Boolean.
'******************************************************************
'* Get the Context from the application
Set m_objContext = GetObjectContext()
'* Boolean for MTS/COM+ or not
m_blnMTS = Not (m_objContext Is Nothing)
End Sub
Private Function ObjectControl_CanBePooled() As Boolean
'******************************************************************
'* ObjectControl_CanBePooled
'* -------------------------
'* One of the methods of the MTS/COM+ ObjectControl interface. This
subroutine
'* is used to specify if this object can be pooled. In Visual Basic 6,
this
'* MUST be set to false.
'******************************************************************
'* Must be set to false in Visual Basic 6
ObjectControl_CanBePooled = False
End Function
Private Sub ObjectControl_Deactivate()
'******************************************************************
'* ObjectControl_Deactivate()
'* --------------------------
'* One of the methods of the MTS/COM+ ObjectControl interface. This
subroutine
'* is used to destroy the object. The ObjectContext is set to nothing
here.
'******************************************************************
Set m_objContext = Nothing
End Sub
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