What does multi_step in world_control.proto do?

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I am trying to execute several steps of Gazebo7 simulation by sending a msgs::WorldControl message to Gazebo where simulation is paused. In effect, I aim to advance the simulation by a varying amount of time. However, regardless of what number I pass using msg.set_multi_step(m_stepCount), I cannot seem to advance by more than 1 iteration.

Did I misunderstand what multi_step does?

Relevant code excerpt from one of my experiments:

    void OnUpdate() 
    {
        // Throttle Publication
        gazebo::common::Time::MSleep(1000);

        m_step_count = m_step_count == 1 ? 700 : 1;

        msgs::WorldControl msg;
        msg.set_multi_step(m_step_count);
        this->pub->Publish(msg);

        // msgs::WorldControl stepMsg;
        // stepMsg.set_step(1);
        // this->pub->Publish(stepMsg);

        std::cout << "Publishing OnUpdate. Steps: " << m_step_count << std::endl;
    }

The result is that every second:

• Iteration increases by 1
• Sim Time increases by 00 00:00:00.001
• Real Time is increased by 00 00:00:01.000
• 700 or 1 are printed in the output string, alternating on every tick