Interfacing Simulink and Gazebo

I'd like to encapsulate a gazebo simulation as an S-function in Simulink. I've written an S-function that should configure itself and publish a gazebo topic message. When this code is compiled as "regular" C+ and run from the command line, it works. But when I copy it into an S-function, compile it with mex, and try to use it in Simulink, it doesn't - for some reason, it sees a small subset of all of the gazebo topics the master knows about.

The pertinent code is:

static void mdlStart(SimStruct *S)
{
    std::string   _master_host;
    unsigned int  _master_port;
    std::list<std::string> topics_list;
    
    gazebo::client::setup();
    gazebo::transport::init("127.0.0.1", 11345);
    gazebo::transport::run();
    gazebo::transport::NodePtr node(new gazebo::transport::Node());
    node->Init("default");

          // This topic will let us issue gazebo single-step commands
    step_cmd = node->Advertise<gazebo::msgs::WorldControl>("/gazebo/default/world_control");

          //std::cout << "Waiting for connection\n";
    //anglepub->WaitForConnection();
    //std::cout << "Got connection\n";
    gazebo::transport::get_master_uri(_master_host, _master_port);
    std::cout << "Host: " << _master_host << " port: " << _master_port << "\n";
      
  topics_list = gazebo::transport::getAdvertisedTopics("");
  for(std::list<std::string>::iterator topic=topics_list.begin(); topic!=topics_list.end(); topic++) {
    std::cout << (*topic) << "\n";
  }
  }

Oddly, it does see some of the topics from the master, just not all of them (and not the ones I need). Also, if I uncomment the "WaitForConnection" line, Simulink hangs at that line.

Yes, I know I could buy the Robotics Toolbox and do this through ROS, but for my particular use case I need finer-grained control over gazebo than the ROS interface provides, so I need to be able to talk directly to a gazebo plugin that I'm writing.

My suspicion is that the environment S-functions run in is in some way nonstandard, but I can't find any documentation about it.