title: Sqlite WAL blocks despite doc sais it doesn't
body: <p>sqlite3_step() frequently returns SQLITE_LOCKED, despite doc saying:</p>
  
  <blockquote>
    <p>WAL provides more concurrency as readers do not block writers and a
    writer does not block readers. Reading and writing can proceed
    concurrently.</p>
  </blockquote>
  
  <p>I have two threads, each has one connection. WAL is turned on, shared cache is turned on. Multithreading mode is chosen (SQLITE_OPEN_NOMUTEX passed when opening). When this problem occurs, the locked thread is only reading (other thread is writing).
    Did I miss something?</p>
  
  <p>Thank You!</p>