title: About logback's AsyncAppender
body: <p>When I check the doc of AsyncAppender in logback, I didn't find something like thread pool setting which support AsyncAppender.</p>
  
  <p>Does that mean there's only 1 thread to consume log events from the blocking queue? (while the log events could be produced by multiple threads, say 20-40)</p>
  
  <p>Thanks</p>
  
  <p>Leon</p>