Sleep pauses entire execution including websocket intervals

[nicodn]

Brief summary

Using sleep() with durations longer than 30 seconds cause our websocket sessions to get disconnected by the server because ping is not firing despite it being in an interval

k6 version

k6 v0.42.0

OS

macOS

Docker version and image (if applicable)

No response

Steps to reproduce the problem

I'm using the experimental support for Websockets & in an setInterval calling socket.ping()

If I add sleep(45) after connecting the websocket, when the sleep ends the server has already disconnected the socket due to lack of pings.

Expected behaviour

Ideally intervals & timers & timeouts should continue despite calls to sleep(), or perhaps a different type of sleep might need to be supported?

Actual behaviour

The ping calls don't get attempted until after sleep() ends. Not sure what the legacy socket behaviour is...

[na--]

The old k6 sleep() function is incompatible with JS event loops, it blocks the whole event loop... :disappointed: It was fine when k6 didn't have an event loop in every VU and everything was synchronous, but now it can be a big problem, as you have seen. This is why other JS runtimes don't have a blocking sleep() function, they have setTimeout() or something like that.

I will move this issue to the docs repository, since we probably need to adjust the documentation and discourage users from using sleep(), given that we have more and more async functions in the k6 JS APIs... cc @mstoykov

perhaps a different type of sleep might need to be supported?

It is, k6 also has setTimeout() and setInterval(), see https://k6.io/docs/javascript-api/k6-experimental/timers/

[mstoykov]

I do wonder though ... what to do?

I do think it is too early to outright be "don't use any syncrhnouns calls - use only async ones". There are both IMO too many sharp corners and not enough support.

Even http.asyncRequest is not enough for http request as anyone wanting to use any of the "html" methods to start request suddenly goes into synchrous http requests calls :(. Fixing that is likely not going to be easy.

I also don't really want to go to every API and be "This is syncrhouns call - do not use with asynchrnous calls if possible." and the reverse :(.

Having a general explanation around synchrouns and asyncrhouns calls and the event loop, seems like the best call - but the again it needs to be linked from everywhere.

So I would prefer if we first figure out what the plan is before somebody spends days writing and editing a ton of pages.

[nicodn]

Thanks for the awesomely rapid feedback guys! Reading your comments helped me grasp the change I had to make and now I'm using either a sleep call to simulate users closing the app and timers to pause user actions while the wss continues in the background

[MattDodsonEnglish]

Do I understand that we should now advise against all sleep calls in favor of some async method? @mstoykov @na--

That's a pretty big change docs-wise. Will require changing a lot of scripts