code: public void register(Client client) {
          Exceptions.checkNotClosed(this.closed.get(), this);
          Preconditions.checkNotNull(client, "client");
          synchronized (this.clients) {
              if (!this.clients.contains(client)) {
                  this.clients.add(client);
                  client.updateGenerations(this.currentGeneration.get(), this.oldestGeneration.get());
              }
          }
  
          log.info("{} Registered {}.", TRACE_OBJECT_ID, client);
      }
docs: Registers the given client to this CacheManager.
  
  @param client The client to register.