code: func (m *RWMutex) Unlock() {
  	m.mu.Unlock()
  	if !Opts.Disable {
  		postUnlock(m)
  	}
  }
docs: // Unlock unlocks the mutex for writing.  It is a run-time error if rw is
  // not locked for writing on entry to Unlock.
  //
  // As with Mutexes, a locked RWMutex is not associated with a particular
  // goroutine.  One goroutine may RLock (Lock) an RWMutex and then
  // arrange for another goroutine to RUnlock (Unlock) it.