Stuck in infinite loop when specifying iterations and VUs

[AlexGustafsson]

Environment

OS: macOS 10.13.6 (17G65)
k6: v0.22.1

What happens

I get stuck in an infinite loop giving me the following output:

running [=====================================================>----] 9429 / 10000
running [======================================================>---] 9648 / 10000
running [========================================================>-] 9927 / 10000
running [========================================================>-] 9994 / 10000
running [========================================================>-] 9994 / 10000
running [========================================================>-] 9994 / 10000
running [========================================================>-] 9994 / 10000
running [========================================================>-] 9994 / 10000
...

Note: the amount of finished iterations seem to vary in the last tens.

How to replicate

1. Download binary to working directory
2. Write the following script to script.js (adapted from the docs)

import http from "k6/http";
import { check, sleep } from "k6";

export let options = {
 stages: [
    { duration: "30s", target: 20 },
    { duration: "1m30s", target: 10  },
    { duration: "20s", target: 0 },
  ]
};

export default function() {
  let res = http.get("http://localhost:3000");
  check(res, {
    "status was 200": (r) => r.status == 200
  });
}

3. Run using ./k6 run --iterations 10000 --vus 100 script.js
4. Watch it get stuck during the last few iterations

[na--]

Ah, I this seems to be because you use both --iterations and also have stages configured in the exported options. If you wait for 2 minutes and 20 seconds (the sum of the stages' duration), the test will finish. And k6 will only make 1000 http requests, so the execution finishes when it's supposed to (whenever one of the end conditions is reached), but then k6 just waits there without exiting... And the problem seems to only happen with stages, not with duration, here's a shorter self-contained example that reproduces the issue without any CLI flags:

import http from "k6/http";

export let options = {
    vus: 10,
    iterations: 100,
    stages: [
        { duration: "60s", target: 20 },
    ],
};

export default function () {
    http.get("https://test.loadimpact.com");
}

Again, when you wait for a minute, k6 will exit successfully, so I'll remove the high prio issue tag. But

[AlexGustafsson]

@na— Thank you for the quick response and thorough explanation! Closing as this is expected behaviour.

[na--]

Wait, that's still a bug, even if it's not a major one 😄 I'll leave the issue open so we don't forget to fix it.