code: public static EventLoopGroup getServerBossEventLoopGroup(ServerTransportConfig config) {
          String type = config.getProtocolType();
          EventLoopGroup bossGroup = serverBossGroups.get(type);
          if (bossGroup == null) {
              synchronized (NettyHelper.class) {
                  bossGroup = serverBossGroups.get(config.getProtocolType());
                  if (bossGroup == null) {
                      int bossThreads = config.getBossThreads();
                      bossThreads = bossThreads <= 0 ? Math.max(4, SystemInfo.getCpuCores() / 2) : bossThreads;
                      NamedThreadFactory threadName =
                              new NamedThreadFactory("SEV-BOSS-" + config.getPort(), config.isDaemon());
                      bossGroup = config.isUseEpoll() ?
                          new EpollEventLoopGroup(bossThreads, threadName) :
                          new NioEventLoopGroup(bossThreads, threadName);
                      serverBossGroups.put(type, bossGroup);
                      refCounter.putIfAbsent(bossGroup, new AtomicInteger(0));
                  }
              }
          }
          refCounter.get(bossGroup).incrementAndGet();
          return bossGroup;
      }
docs: 得到服务端Boss线程池
  
  @param config 服务端配置
  @return 服务端Boss线程池