System plugins keep executing after their model is removed.

[jrutgeer]

Environment

• OS Version: Ubuntu 22.04
• Harmonic, source built

Description

Many system plugins need to be attached to a model (e.g. to access that model's links, collisions, etc).
However, when that model is removed, the plugin keeps running.
Given typically a model plugin needs to access entities of the model (that no longer exist), this leads to crashes.

Expected behavior

When a model is removed, all of its plugins are removed as well, or at the least their pre/update/post methods are no longer called.

Steps to reproduce

• Create a trivial system plugin, e.g.

void TrivialPlugin::PreUpdate(const gz::sim::UpdateInfo &_info,
                         gz::sim::EntityComponentManager &_ecm)
{
  if (_info.paused) return;

  static int counter = 0;
  counter++;
  if (1000 == counter)
  {
    counter = 0;
    std::cout << "TrivialPlugin::PreUpdate" << std::endl;
  }
}

• Add this plugin to a model.

• Start the simulation

• Select the model in the Entity Tree, right click + 'remove'

• The model is removed, but the cout message is still being output to the terminal.

[jrutgeer]

I implemented a simple workaround like this:

void WasteBin::PostUpdate(const UpdateInfo & _info, const EntityComponentManager & _ecm)
{
  if (_info.paused) return;
  if (!this->dataPtr->configured) return;

  if (!this->dataPtr->model.Valid(_ecm))
  {
    gzwarn << "Model <" << this->dataPtr->modelName << "> no longer valid. "
           << "Disabling WasteBin plugin." << std::endl;
    this->dataPtr->configured = false;
    return;
  }

  [...]

}

While this works well, it has following drawbacks:

• It is yet some additional code to implement in each model or sensor plugin; prone to be forgotten etc.
• I assume the call to model.Valid(_ecm) has a non-negligable computational cost, which would be avoided if a proper solution was implemented.

So I still feel that model and sensor plugins should be disabled (or removed) automatically upon removal of the corresponding model or sensor.

[jrutgeer]

Another example:

• Add a model with some joints having a JointPositionController plugin,
• Remove that model

Result:

Flood of error messages:

[Err] [EntityComponentManager.cc:1083] Trying to create a component of type [8319580315957903596] attached to entity [47], but this entity does not exist. This create component request will be ignored.

I 'fixed' this in my local tree with a similar workaround as above, but meh...

void JointPositionController::PreUpdate(
    const UpdateInfo &_info,
    EntityComponentManager &_ecm)
{
  GZ_PROFILE("JointPositionController::PreUpdate");

  if (kNullEntity == this->dataPtr->model.Entity())
  {
    return;
  }

  if (!this->dataPtr->model.Valid(_ecm))
  {
    gzwarn << "JointPositionController model no longer valid. "
           << "Disabling plugin." << std::endl;
    this->dataPtr->model = Model(kNullEntity);
    return;
  }

  [...]

}

[arjo129]

Yes currently the SystemManager does not support removal of plugins. This seems to be something that can be fixed, but will take some amount of effort.

[frede791]

Latching on to this: I get an entity does not exist error after removing a model that was spawned using the resource spawner. I think this is probably related to this issue. (Using gazebo garden)

[arjo129]

Yeah. That is expected I'm currently working on a fix for it here: #2232

[arjo129]

Fixed by #2232