Article ID: 271787 - Last Review: June 25, 2004 - Revision: 2.1

PRB: Application.Lock and Application.UnLock Cause Server to Hang in IIS 5.0

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This article was previously published under Q271787

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SYMPTOMS

When you modify Application variables from within a component that is called from an Active Server Pages (ASP) page, your server may stop responding (hang). The code in the component that causes the problem resembles the following: 
Application.Lock
Application("myvar") = "hello world"
Application.UnLock
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CAUSE

Code that is embedded in the Application.Lock and Application.UnLock methods provides protection in a multi-user environment. With the introduction of COM+, Internet Information Server (IIS) 5.0 takes advantage of the Thread-Neutral Apartment (NA) when accessing the Application object. As a result, when you explicitly call Application.Lock and Application.UnLock from within a component, under certain scenarios you might encounter a deadlock scenario that causes the server to stop responding. This problem is most commonly seen when ASP intrinsics are marshalled back and forth between the IIS server and the COM+ Application server. The following two scenarios may cause the server to hang:
  • When you debug a Microsoft Visual Basic component from the Visual Basic Integrated Development Envrionment (IDE).
  • When you call a component that is running as a Server application in COM+.
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RESOLUTION

The Application.Lock and Application.UnLock methods are not needed to assign a single Application variable because the methods are called internally.

If you need to assign multiple Application variables within the same Application.Lock and Application.UnLock methods from your component, your component must run in the same process as the caller, or you must modify your logic to only include a single assignment. For example, the following code 
Application.Lock
Application("myvar1") = "hello"
Application("myvar2") = "world"
Application.UnLock
could be modified to work around this issue as follows: 
Dim array(1)
array(0) = "hello"
array(1) = "world"
Application("myvar") = array
NOTE: This is only one example. There are numerous ways that you can change your logic to work around this issue.
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MORE INFORMATION

Steps to Reproduce Behavior

  1. In Visual Basic, create a new ActiveX DLL project.
  2. Add a reference to the following libraries:
    COM+ Services Type Library
    Microsoft Active Server Pages Object Library
  3. Add the following code to the class module:
    Implements ObjectControl

Private oContext As ObjectContext
Private oApplication As ASPTypeLibrary.Application

Private Sub ObjectControl_Activate()
    Set oContext = GetObjectContext()
    Set oApplication = oContext("Application")
End Sub

Private Sub ObjectControl_Deactivate()
    Set oContext = Nothing
    Set oApplication = Nothing
End Sub

Private Function ObjectControl_CanBePooled() As Boolean
    ObjectControl_CanBePooled = False
End Function

Public Sub IISHang()

    oApplication.Lock
        oApplication("test") = "World"  '<= App HANGS here
    oApplication.UnLock

End Sub
  4. Compile the DLL and register the component with COM+. Make sure that the COM+ package's Activation type is set to Server application.
  5. Create a new ASP page and paste the following code:
    <%
    Dim obj
    Set obj = Server.CreateObject("Project1.Class1")
    Call obj.IISHang()
    Set obj = nothing
%>
  6. Run the ASP page to cause the server to stop responding.
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APPLIES TO
  • Microsoft Internet Information Services 5.0
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Keywords: 
kbprb KB271787
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