title: Serial queus and sync operations
body: <p>im studying multithreading and what i want is some clarification on subject matter.</p>
  
  <p>As far as i know, <strong>SERIAL</strong> queue execute tasks serially, are always executing one task at a time.</p>
  
  <p>Now, <strong>SYNCHRONOUS</strong> function is a function, that returns only after all tasks complete.</p>
  
  <p>Now, i'm a bit confused. What difference between those two? </p>
  
  <p>if i understand correct, both of them will <strong>block</strong> current thread (if they are not "covered" in global concurrent queue), and both of them execute tasks exactly in FIFO order.</p>
  
  <p>So, what exactly a difference between them? Yes, i understand that serial is a property of a queue, and sync is a function (or operation). But their functionality is like to be similiar.</p>