title: How to create a thread safe singleton in vala?
body: <p>I want to create a thread-safe singleton instance for my vala class.</p>
  
  <p>As you know, singletons may lead to <a href="https://softwareengineering.stackexchange.com/questions/164929/is-the-singleton-pattern-prone-to-thread-safety-problems">threading issues</a> if not properly implemented.</p>