title: Asynchronous wait for an condition to be met
body: <p>In my code I have three variables whose value depend on an external function call, they can be set to true in any moment and in any order, so, they are more like flags.</p>
  
  <p>I need a function to be only once these three variables are set to true.</p>
  
  <p>How can I perform a wait for these three variables to be true, without blocking my server, in an asynchronous way?</p>
  
  <p>(I do not want to be refered to external libraries)</p>