Events and race conditions

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Events and race conditions

Friday, March 19, 2004 11:30 AM

JayBaz points out something that is worth keeping in mind about events: they can be subject to race conditions in multi-threaded scenarios. In VS 2002 and VS 2003, you'll need to do what the C# folks do and handle the race condition yourself:

Event Moved(ByVal x As Integer, ByVal y As Integer)

Sub Move(ByVal x As Integer, ByVal y As Integer)
  Dim temp As MovedEventHandler = Me.MovedEvent

  If Not temp Is Nothing Then
    temp(x, y)
  End If
End Sub

(The names "xEventHandler" and "xEvent" are automagically generated names - the first is the delegate type of the event and the second is the hidden field generated to hold the event delegate.)

In Whidbey, however, we've changed the code generation for RaiseEvent so that this will be done automatically for you. We work hard so you don't have to!

Feedback

# re: Events and race conditions

Is there any way to implement as the follow C# codes in Visual Basic 2005? public event EventHandler MyEvent { add { _MyEvent += value; } remove { _MyEvent -= value; } } I think it is an important feature. 3/20/2004 3:13 AM | Ninputer

# re: Events and race conditions

Not today, but we are planning the feature for Whidbey! 3/20/2004 11:46 AM | Paul Vick

# re: Events and race conditions

Just a note on something that caused me some confusion: if the event implements an event on an interface, the event handler is defined on the interface as well, not on the implementing class:
Public Interface IFoo
Event DidFoo()
End Interface

Public Class Foo
Implements IFoo

Event DidFoo Implements IFoo.DidFoo
Public Sub DoFoo()
Dim temp As IFoo.DidFooEventHandler = Me.DidFooEvent
If Not temp Is Nothing Then
temp()
End If
End Sub
End Class 3/31/2004 1:52 PM | Eric

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