How to create Singleton with async method?
<p>I want to have an singleton, say <code>Printer</code>, with one method, say <code>bool addToPrintQueue(Document document)</code>. <code>addToPrintQueue</code> should be async (should return immediately), return <code>true</code> if added to queue and <code>false</code> if document already in <code>queue</code>. How to write such method and what should I use for <code>queue</code> processing? (should it be separate thread?)</p>
