VB.NET RaiseEvent, threadsafe?

Question

Is RaiseEvent thread safe?

In C# you write

if (event != null)
{
    event.invoke();
}

and the C# code is not thread safe....

Answer 1

In C# you rather write:

EventHandler h= myEvent;
if (h!=null)
   h(...);

This avoids the obvious problem (i.e. the unsubscribing between the test and the call), but this isn't thread-safe either.

Calling an event implies the listener is ready to process this event. This heavily depends on your specific situation, and is usually achieved through the use of synchronization mechanisms.

What exactly do you mean by "Thread safe" ?

Answer 2

If I need to do thread safe events, I write this:

Class Test

    Public Event Click(ByVal sender As Object, ByVal e As EventArgs)
    Public Event MouseIn(ByVal sender As Object, ByVal e As EventArgs)

    Private Delegate Sub EventArgsDelegate(ByVal e As EventArgs)
    Private ReadOnly _parent As Control

    Public Sub New(ByVal parent As Control)
        _parent = parent
    End Sub

    Private Sub OnClick(ByVal e As EventArgs)

        If _parent.InvokeRequired Then
            _parent.Invoke(New EventArgsDelegate(AddressOf OnClick), e)
        Else
            RaiseEvent Click(Me, e)
        End If

    End Sub

    Private Sub OnMouseIn(ByVal e As EventArgs)

        If _parent.InvokeRequired Then
            _parent.Invoke(New EventArgsDelegate(AddressOf OnMouseIn), e)
        Else
            RaiseEvent MouseIn(Me, e)
        End If

    End Sub

End Class

Then whenever I need to raise the event I just use the OnClick(new eventargs(...)), etc. If you use Reflector you can observe that most thread safe controls use a similar system.