code: public boolean addHandler(PacketHandler handler) {
          synchronized (this.handlers){
              if (!handlers.contains(handler)) {
                  handlers.add(handler);
                  this.count.incrementAndGet();
                  Collections.sort(this.handlers, REVERSE_COMPARATOR);
                  return true;
              }
              return false;
          }
      }
docs: Registers a new packet handler in the pipeline.<br>
  Cannot register same handler twice.
  
  @param handler The handler to be registered.
  @return Whether the handler was successfully registered or not.