code: func (m *lockingMap) Get(key string) (interface{}, bool) {
  	m.keyLocker.RLock(key)
  	defer m.keyLocker.RUnlock(key)
  
  	m.lock.RLock()
  	defer m.lock.RUnlock()
  
  	val, ok := m.data[key]
  	if ok && (m.checkFunc == nil || m.checkFunc(key, val)) {
  		return val, true
  	} else {
  		// No value or it failed to check
  		return nil, false
  	}
  }
docs: // Get returns the value, ok for a given key from within the map. If a ValueCheckFunc
  // was defined for the map, the value is only returned if that function returns true.