Locust distributed mode: "Unknown message type '_distributor_request' from worker.." warning halts users

I am using Locus in distributed mode with 1 master and n workers to run a load test.

I am also using the locust-plugins library to utilize its Distributor utility. My goal is to preallocate one unique resource per user (from a list of “items”) and ensure each virtual user gets a unique item during the test. Here's a simplified outline of my setup:

Master node: Generates a list of items (one for each user) at test start. It then broadcasts this list to all workers using a custom message. Workers: Upon receiving the items message, each worker stores the list and prepares to use it for its users. I use a Distributor instance on each worker to serve the models to the user tasks.

Master sending the resource list (at test start):

@events.test_start.add_listener

def on_test_start(environment, **kwargs):
    if environment.runner is not None and environment.runner.master:
        # Master generates the list of resources for all users
        models = generate_items(total_user_count)
        # Send the list to all workers
        environment.runner.send_message("items_models", {"items_models": models})

Worker receiving and storing the list:

items_models_dist = None
        
def set_items_models(env, msg, **kwargs):
    global items_models_dist
    received_list = msg.data["items_models"]
    env.logger.info(f"Worker received {len(received_list)} items models. Proceeding...")
    items_models_dist = Distributor(env, iter(received_list))
            
    

@events.init.add_listener
    def on_worker_init(environment, **kwargs):
        if isinstance(environment.runner, runners.WorkerRunner):
            environment.runner.register_message("items_models", set_items_models)

User task using the Distributor:

class MyUser(HttpUser):
    @task
    def use_model(self):
        model = next(items_models_dist)

When I hit model = next(items_models_dist), I am getting: "Unknown message type received from worker worker.some.id (index 0): _distributor_request" and the user halts.

I did not explicitly call or register any handler for "_distributor_request" in my code. I assumed the plugin would take care of it. The warning and lack of user spawn suggests something is fundamentally wrong with how I’m using the plugin in distributed mode. Help?

Locust version: 2.32.3 Python version: 3.12.3 locust-plugins version: 4.5.3

I am running in distribution mode on one machine with command line: locust -f test.py --processes -1

You're supposed to initialize the Distributor object on both master and worker instances, like in the example here: https://github.com/SvenskaSpel/locust-plugins/blob/602d68e7d4bd77d3a0d2c20afa05b71f7557b547/examples/distributor_ex.py#L22 (just leave the iterator argument set to None on the workers)

There is no need to "manually" register any custom message handlers or call send_message if you're using Distributor.