Reentrancy Problem

A activex control is refered in my VB project,I get a message when the control fire an event.but I find that
when I processes a message with this event,this event is triggered again before the processing for the original message is finished.
uses a global BOOL variable to detect reentrancy maybe helpful,but some messages will be lost in this way.
any help on this subject would be very appreciated.
fenghoodAsked:
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WalterMConnect With a Mentor Commented:
Sorry fenghood, but my experience in VB multithreading is limited to some samples I've studied now and then.

VB does support it to a certain degree, i.e. apartment-model threading, but no free-threading.

You might be able to obtain some useful information concerning multithreading and firing events by following these MSDN links:

"Events: From an ATL Server to a Visual Basic Sink"
http://msdn.microsoft.com/library/techart/msdn_atlevnts.htm

"PRB: Firing Event in Second Thread Causes IPF or GPF"
http://support.microsoft.com/support/kb/articles/Q196/0/26.ASP

"SAMPLE: ATLCPImplMT Encapsulates ATL Event Firing Across COM Apartments"
http://support.microsoft.com/support/kb/articles/Q280/5/12.ASP

"Fireev.exe Fires Events from a Second Thread"
http://support.microsoft.com/support/kb/articles/q157/4/37.asp

Michel
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Richie_SimonettiIT OperationsCommented:
We need to know how this event is triggered.
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fenghoodAuthor Commented:
Richie simonetti:
  I fire this event using COleControl::FireEvent function
in VC++,when I get some messages,this event is fired at the
end of each message handler.
  need your help,thanks.
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fenghoodAuthor Commented:
Richie simonetti:
  I fire this event using COleControl::FireEvent function
in VC++,when I get some messages,this event is fired at the
end of each message handler.
  need your help,thanks.
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WalterMCommented:
It may be the case that one of the statements in your VB event handler implementation retriggers the event, e.g. if you manipulate the ActiveX control from within the event handler by calling one or more member functions.

If it is desirable behaviour that touching these control members raises an event, simply protect the VB event handlers from reentry by using a local static Boolean flag, i.e.

Private Sub YourEventHandler()
    Static ReEntry As Boolean
   
    If ReEntry Then Exit Sub
    ReEntry = True
   
    '... implementation code ...
   
    ReEntry = False
End Sub

Note that VB itself also shows this behaviour sometimes, e.g. if you change a form's size form within the Resize event, reentry will occur and you need to protect the Form_Resize event handler in the same way.

Michel
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Richie_SimonettiIT OperationsCommented:
fenghood, Michel post would help you.
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fenghoodAuthor Commented:
WalterM :
  any more,if I create a thread in Activex control with
CreateThread() function,how does VB deal with this?
  As we know,VB don't support mutil-threaded,VB application' thread pool is set to 1 thread by default and can't be changed.My Activex control is apartment thread model,apartment should reside in the thread that create
object of control.
  I can't understand this very clearly,would u help me?
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fenghoodAuthor Commented:
thanks a lot
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WalterMCommented:
Thanx for the points, fenghood, hope the articles help.

Michel
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fenghoodAuthor Commented:
they are very helpful :)
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