Question

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Checking for null before event dispatching… thread safe?
Raise event thread safely – best practice

protected void NotificationEvent(Object sender, EventArgs e)
{
    // Copy to a temporary variable to be thread-safe
    EventHandler<EventArgs> tmp = mNotification;
    if (tmp!= null)
    {
        tmp(this, null);
    }
}

How does copying mNotification makes it thread-safe. Can someone explain?

Answer 1

If it were

if (mNotification!=null)
{
    mNotification(this, null);
}

mNotification could be set to null by another thread between if (mNotification!=null) and mNotification(this, null);