code: protected synchronized void initialize() {
          String invocationServiceName = this.invocationServiceName;
          invocationService = (InvocationService)
                  CacheFactory.getService(invocationServiceName);
          if (invocationService == null) {
              throw new IllegalArgumentException("Invocation service ["
                                                 + invocationServiceName
                                                 + "] is not defined.");
          }
  
          invocationService.addMemberListener(this);
          serviceMembers = invocationService.getInfo().getServiceMembers();
          memberIterator = serviceMembers.iterator();
      }
docs: Initialize this executor service.