Question regarding Events in John Skeet's book C# in Depth

I'm studying C# Events on this link and am a little lost on when the following code is called in the context of Main()

/// <summary>
/// Raises the SomeEvent event
/// </summary>
protected virtual OnSomeEvent(EventArgs e)
{
    SomeEventHandler handler;
    lock (someEventLock)
    {
        handler = someEvent;
    }
    if (handler != null)
    {
        handler (this, e);
    }
}

It's code that is right above the sentence

"You c开发者_开发知识库ould use a single lock for all your events"

Question:

How or when does "OnSomeEvent" get called? I'm not asking about variable locking (as-is the context of the code sample) rather, I'm asking when does the protected virtual method pasted above get called?

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The class calls OnSomeEvent when it wants to fire off the event.