Could not load custom component

Hi, I am working on adding the “FollowPath” goal behavior to carter_sim and adding my own node to pass the required Plan2Proto to the FollowPath node. I seem to have successfully added the FollowPath node, but I am running into issues adding my own custom node. Herein it is referred to as arena_pattern_gen with the codelet name ArenaPatternGen.

From what I understand, in addition to having my cpp and hpp files in the app directory, I should register the codelet in the header(hpp) file using the line


then, add the node under navigation.graph.json (as it interacts with the navigation graph) and add the codelet as a component, under the type name registered in the header file:

      "name": "arena_pattern_gen",
      "components": [
          "name": "message_ledger",
          "type": "isaac::alice::MessageLedger"
          "name": "arena_pattern_gen",
          "type": "ArenaPatternGen"

and the edges:

      "source": "arena_pattern_gen/arena_pattern_gen/plan",
      "target": "follow_path/isaac.navigation.FollowPath/plan"

and the tick period in the navigation.config.json:

"arena_pattern_gen": {
    "arena_pattern_gen": {
      "tick_period": "250ms"

Finally, in the BUILD file, I add “isaac_cc_module” to the load() call and define the module:

    name = "arena_pattern_gen",
    srcs = ["ArenaPatternGen.cpp"],
    hdrs = ["ArenaPatternGen.hpp"],
    visibility = ["//visibility:public"],
    deps = [

and add it to the carter_sim app under “modules”:

    name = "carter_sim",
    app_json_file = "",
    data = [
    modules = [
[b]        "//apps/carter_sim:arena_pattern_gen",
[/b]        "navigation",

However, when I try to run this I get the error:

engine/alice/backend/modules.cpp@271: Could not load component 'ArenaPatternGen'

I seem to be following all guides I can find to the letter. I have tried registering and referencing the codelet name both with and without the isaac:: namespace but this does not seem to make a difference.

I would appreciate it if anyone has experience with a problem like this, or any insight in general. I am willing to provide my full code here if it will help.

Thanks for reading!

  • Travis

Hi Travis,

I had a similar issue. For some reason when modules are in subfolders in the apps directory they do not load correctly/consistantly. Try this:

Make a new folder in /packages
put your build file here containing your module declaration
put your hpp and cpp files here
reference this from your carter project

otherwise everything else looks correct. Let me know how it goes.

Hi FedoraLabs,

Thanks for your input. I was actually able to include this module in the same directory and in the same build file (though this may not be ideal for re-using this module in the future), all I really needed to add was the entry to the under modules:

"modules": [

Although this led to a new error:

ERROR   engine/alice/backend/modules.cpp@241: apps/carter_sim:arena_pattern_gen: apps/carter_sim/ undefined symbol: _ZN5isaac15ArenaPatternGen4stopEv

This was apparently due to my having declared start(); tick(); and stop(); in the header file without defining a stop() function in my c++ code. Adding a stop() function definition resolved this error.

This got all the nodes running - I’ve run into a further issue but will probably make a new post to describe that.

Thanks again for your help!