code: func (e *ErrorsTotalMap) retrievePointerFor(err HTTPError) *uint64 {
  	serr := simplifyHTTPError(err)
  	e.lock.RLock()
  	ptr, ok := e.counter[serr]
  	e.lock.RUnlock()
  	if ok {
  		return ptr
  	}
  
  	// For pointer creation, a write-lock is required
  	e.lock.Lock()
  	// We ensure that the pointer wasn't created in the meantime
  	if ptr, ok = e.counter[serr]; !ok {
  		ptr = new(uint64)
  		e.counter[serr] = ptr
  	}
  	e.lock.Unlock()
  
  	return ptr
  }
docs: // retrievePointerFor returns (after creating it if necessary) the pointer to
  // the counter for the error.