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How to wait until model is loaded while not blocking the other processes

asked 2020-04-20 09:12:37 -0500

kumpakri gravatar image

updated 2020-04-24 01:28:02 -0500

I have a World plugin in which I need a pointer to a particular model's link. The problem is, that this plugin gets loaded before the model, therefor accessing the model's link results in failure. I tried to wait until the model is loaded as shown below.

        physics::ModelPtr model = this->world->GetModel(model_name);
        while(model == NULL) {
            model = this->world->GetModel(model_name);

But this seems to induce a neverending loop. The model never gets loaded. I tried putting c++ usleep() and roscpp ros::Duration(0.5).sleep() in attempt to let the other processes load the world and the models in the meanwhile, but that does not help. Gazebo stucks in this loop.

Is there any way how to solve this?


Ok, so I used the solution suggested by nlamprian, just declaring the event::ConnectionPtr as a class variable. But at the moment when the event callback was called, the robot was still not fully loaded in Gazebo. So I just set a flag inside this callback function and I get the pointer to the model in the next call of the OnUpdate function (which is called on every simulation time step).

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answered 2020-04-20 11:49:57 -0500

nlamprian gravatar image

You can register to the add entity event, and do the initialization asynchronously.

event::ConnectionPtr add_entity_connection = event::Events::ConnectAddEntity(
    std::bind(&MyWorldPlugin::addEntityEventCallback, this, std::placeholders::_1));

void MyWorldPlugin::addEntityEventCallback(const std::string &name) {
    // Check entity name...
    // Trigger initialization...
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So this ConnectAddEntity event is triggered when any model is spawned/created in the world? Or how does this work?

kumpakri gravatar imagekumpakri ( 2020-04-21 00:41:20 -0500 )edit

It's triggered when a model or actor is created.

nlamprian gravatar imagenlamprian ( 2020-04-21 01:09:11 -0500 )edit

out of top of your head, is there any common mistake with using those events that could prevent my plugin to register the callback function? I tried this and it compiles without error, but the callback function is never called.

kumpakri gravatar imagekumpakri ( 2020-04-22 10:50:55 -0500 )edit

Did you maybe define event::ConnectionPtr as a local variable? In such case, the connection is destroyed immediately.

nlamprian gravatar imagenlamprian ( 2020-04-22 13:36:34 -0500 )edit

@nlamprian Yes. Yes I did. Thank you!

kumpakri gravatar imagekumpakri ( 2020-04-23 03:45:00 -0500 )edit
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Asked: 2020-04-20 09:12:37 -0500

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Last updated: Apr 24 '20