guava/src/com/google/common/collect/Multimaps.java
public static <K, V> SetMultimap<K, V> synchronizedSetMultimap(SetMultimap<K, V> multimap) {
    return Synchronized.setMultimap(multimap, null);
  }
public static <K, V> SetMultimap<K, V> synchronizedSetMultimap(SetMultimap<K, V> multimap) {
    return Synchronized.setMultimap(multimap, null);
  }
public static < K , V > SetMultimap < K , V > synchronizedSetMultimap ( SetMultimap < K , V > multimap ) { return Synchronized . setMultimap ( multimap , null ) ; }
Returns a synchronized (thread-safe) {@code SetMultimap} backed by the specified multimap.

<p>You must follow the warnings described in {@link #synchronizedMultimap}.

<p>The returned multimap will be serializable if the specified multimap is serializable.

@param multimap the multimap to be wrapped
@return a synchronized view of the specified multimap
Returns a synchronized ( thread - safe ) { @code SetMultimap } backed by the specified multimap .