updating Dictonary code with ConcurrentDictonary : I'm trying to update the following code to use a ConcurrentDictionary. I appreciate any help.

<pre><code>

    private Dictionary (string, SymbolOrderBook) books = new Dictionary(string, SymbolOrderBook)();

    SymbolOrderBook book;

    lock (books)
    {
        if (!books.TryGetValue(symbol, out book))
        {
            book = new SymbolOrderBook(symbol);
            books.Add(symbol, book);
        }
    }



</code></pre>


Thank you!

