events.init.add_listener runs after Users are created on worker

Describe the bug

It appears that locust.User tasks are executed before all events.init.add_listener listeners are executed on the worker.

Expected behavior

locust.User tasks should execute only after all events.init.add_listener listeners have run.

Actual behavior

It appears that locust.User tasks are executed before all events.init.add_listener listeners are done.

Steps to reproduce

# start worker
python3 -m locust -f test_locustfile.py --headless --worker --master-host=<ip>
# start master
python3 -m locust -f test_locustfile.py --headless --master --expect-workers=1

@events.init.add_listener
def on_locust_init(environment, **_kwargs):
    time.sleep(2)
    log.info('Ran init')

class CustomUser(User):
    @task
    def test(self):
        log.info('Running test')

Output from worker

Spawning 1 users at the rate 1 users/s (0 users already running)...
All users spawned: CustomUser: 1 (1 total running)
Running test
Running test
...
Running test
Ran init
Starting Locust 1.4.3
Running test
...

Environment

• OS:Linux
• Python version: 3.7
• Locust version: 1.4.3
• Locust command line that you ran: given above
• Locust file contents (anonymized if necessary): given above

[delulu]

The tricky thing is that the init event is fired after the initialization of runner, while in the initialization of WorkerRunner it will send a “client_ready” msg to the master right away for being ready to execute the tasks.

It broke the purpose of init event, and it seems there’s no good way to monitor the completion of all init tasks then execute tasks later.

Maybe we can add another method to decouple the emitting of “client_ready” from the initialization of WorkerRunner.

@cyberw please let me know if it looks good to you, I can add a fix.

https://github.com/locustio/locust/blob/94e16dda0aa7bc5735d5d2db13031bfe416a7ab1/locust/main.py#L238

https://github.com/locustio/locust/blob/94e16dda0aa7bc5735d5d2db13031bfe416a7ab1/locust/main.py#L303

https://github.com/locustio/locust/blob/94e16dda0aa7bc5735d5d2db13031bfe416a7ab1/locust/runners.py#L743

[jbarz1]

I’ll see if I can take a crack at it next week. But if someone else wants to attempt a fix, please go ahead 😄