code: public static <K, V> BiMap<K, V> synchronizedBiMap(BiMap<K, V> bimap) {
      return Synchronized.biMap(bimap, null);
    }
docs: Returns a synchronized (thread-safe) bimap backed by the specified bimap. In order to guarantee
  serial access, it is critical that <b>all</b> access to the backing bimap is accomplished
  through the returned bimap.
  
  <p>It is imperative that the user manually synchronize on the returned map when accessing any
  of its collection views:
  
  <pre>{@code
  BiMap<Long, String> map = Maps.synchronizedBiMap(
  HashBiMap.<Long, String>create());
  ...
  Set<Long> set = map.keySet();  // Needn't be in synchronized block
  ...
  synchronized (map) {  // Synchronizing on map, not set!
  Iterator<Long> it = set.iterator(); // Must be in synchronized block
  while (it.hasNext()) {
  foo(it.next());
  }
  }
  }</pre>
  
  <p>Failure to follow this advice may result in non-deterministic behavior.
  
  <p>The returned bimap will be serializable if the specified bimap is serializable.
  
  @param bimap the bimap to be wrapped in a synchronized view
  @return a synchronized view of the specified bimap