docs: @Override
      public final boolean retainAll(Collection<?> c) {
          this.writeLock.lock();
          try {
              int newSize = 0;
              for (final Queue<T> queue : this.keyedQueues.values()) {
                  queue.retainAll(c);
                  newSize += queue.size();
              }
  
              // Update the queue size
              final int oldSize = this.size;
              this.size = newSize;
  
              // If the updated size and old size differ things changed
              return this.size != oldSize;
          } finally {
              this.writeLock.unlock();
          }
      }