code: public static Object runAsServer() {
          LinkedHashMap<ThreadIdentityService, Object> token = null;
  
          if (!checkForRecursionAndSet()) {
              try {
                  for (int i = 0, size = threadIdentityServices.size(); i < size; ++i) {
                      ThreadIdentityService tis = threadIdentityServices.get(i);
                      if (tis.isAppThreadIdentityEnabled()) {
                          if (token == null) {
                              token = new LinkedHashMap<ThreadIdentityService, Object>();
                          }
                          token.put(tis, tis.runAsServer());
                      }
                  }
              } finally {
                  resetRecursionCheck();
              }
          }
          return token == null ? Collections.EMPTY_MAP : token;
      }
docs: Set the server's identity as the thread identity.
  
  @return A token representing the identity previously on the thread.
  This token must be passed to the subsequent reset call.