public boolean isDeadServer(ServerName sn) {
    if (sn.getStartcode() <= 0) {
      return false;
    }

    for (ServerName dead : deadServers) {
      if (
        dead.getStartcode() >= sn.getStartcode() && dead.getPort() == sn.getPort()
          && dead.getHostname().equals(sn.getHostname())
      ) {
        return true;
      }
    }

    return false;
  }
Check if we know if a server is dead.
@param sn the server name to check.
@return true if we know for sure that the server is dead, false otherwise.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/ClusterStatusListener.java