Async Queue – One of my favorite programming interview questions

https://davidgomes.com/async-queue-interview-ai/

by davidgomes • 1 year ago

255 310 1 year ago

Hmm… this code doesn’t work in the real world unless you only run it on a single machine. Perhaps a more interesting question is how to make a multi-node queue with max N concurrent requests.

davidgomes2• 1 year ago

The whole point of this interview is that the candidate is operating on a single-threaded environment.

ramon156• 1 year ago

These are multiple assumptions "This queue is only on one machine and on one thread", what's the real world use-case here? Not saying there's none but make it clear. I wouldn't want to work for a company that has to think of some random precise question instead of e.g. "when would you not use mysql?"

dudeinjapan2• 1 year ago

I guess I don’t want to hire candidates who assume the world is single-threaded

jonchurch_3• 1 year ago

This is handled in the framing of the question:

“… it doesn't ever have to handle more than one request at once (at least from the same client, so we can assume this is a single-server per-client type of architecture).“

For sure a multithreaded async queue would be a very interesting interview, but if you started with the send system the interview is constructed around youd run out of time quickly.

reillyse4• 1 year ago

I dunno, seems like a really confusing question. Communication is important but I can imagine that explaining this verbally on the spot to an interviewee would not be straightforward especially because the assumptions made around single threading get confusing. If it's just a Javascript question say that - because it seems it basically is. Writing this in go would be super easy so I think the question is just asking people how well they understand Javascript.

qu0b• 1 year ago

Yeah, I really don’t see how this is a sensible interview question. It does not even mention async await syntax. Expecting knowledge on callbacks seems dated.

numbsafari• 1 year ago

seems like a really confusing question

Agreed. ‘sendOnce’ implies something very specific in most async settings and, in this interview question, is being used to mean something rather different.

isbvhodnvemrwvn2• 1 year ago

That makes it even better, the candidate should ask clarifying questions. I've worked with people who, when encountering some amount of ambiguity, either throw their hands up, or make some random assumptions. Ability to communicate effectively to bridge the gaps in understanding is what I'd expect from any candidate, especially more senior ones.

mgfist• 1 year ago

Sure, but this isn't a back&forth interview - it's a blog post. The author could have included a section with clarifying questions they expect the candidate to ask, and responses to those questions.

As it stands, we still don't know why the server was broken in this way and why they created a work around in the client instead of fixing the server.

dakiol3• 1 year ago

But that doesn’t work. One could ask why server can handle only one request? Why can’t we upgrade (vertically or horizontally) the server? Why the logic needs to live in the client? And a large etc.

It’s not the ability to communicate effectively that’s at play here, it’s your ability to read your interviewer’s thoughts. Sure thing, if you work with stakeholders, you need some of that as well, but you typically can iterate with them as needed, whereas you have a single shot in the interview.

Plenty of times, at the end of the interview, I do have a better mental picture of the problem and can come up with a way better solution, but “hey, 1h has already passed so get the fuck out of here. Next!”

gopher_space• 1 year ago

The confusing part for me is why I’m dicking around with the client when the server’s broken.

MontyCarloHall• 1 year ago

Exactly. If I were asked this question during an interview, the first thing I'd say is "why should the client bother with anything more complex than jittered exponential backoff?"

mikeocool• 1 year ago

FWIW I’ve basically been given basically this exact requirement by a partner with a crappy API.

We’d get on calls with them and they’d be like “you can’t do multithreading!” we eventually parsed out that what they literally meant was that we could only make a single request to their API at a time. We’d had to integrate with them, and they weren’t going to fix it on their side.

(Our solve ended being a lot more complicated than this, as we had multiple processes across multiple machines that were potentially making concurrent requests.)

rustyminnow• 1 year ago

Because it was written in ALGOL 60, none of the mainframe devs are willing to touch that code, and the dozen other clients probably depend on the broken functionality.

Jarwain3• 1 year ago

I've had to implement this exact logic at work, because we have to talk to devices using modbus tcp, where a lot of devices only supports having one active request per connection at a time. One device we talk to only supports having 5 active connections to it.

Xss3• 1 year ago

I implemented an incredibly similar async queue logic for a CLI tool with the option to build sequences of commands

layer8• 1 year ago

Because you only control the client, but you need to integrate with that broken server of a third party. It’s a pretty common situation to find oneself in.

lazyant• 1 year ago

A server that has a spike of load and can't cope with it is pretty normal, hard to characterize as "broken".

When the client(s) can send more work than the server can handle there are three options:

  1 - Do nothing; server drops requests. 
  2 - Server notifies the clients (429 in HTTP) and client backs-off (exponential, jitter). 
  3 - Put the client requests in a queue.

Interview question/solution does 2 in a poor way (just adding a pause), it's part of the client and does 3 in the client, when usually this is done in an intermediate component (RMQ/Kafka/Redis/Db/whatever).

trhway2• 1 year ago

Absolutely. And it isn’t just about JS, it is about the JS style thinking.

ZiiS• 1 year ago

Interviews are a two way street. If you strongly imply that working around servers that only do one thing is part of your day to day work, a lot of people will want to work somewhere they can learn about more modern software.

armitron• 1 year ago

This is one of the most confusing and badly worded interview problems I've ever seen. If I had been given this problem, I'd view it as a signal that I'd be wasting my time working with the folks that thought it was good.

jonchurch_3• 1 year ago

Maybe I came into this article knowing too much about the solution, but I dont agree with commenters saying this is a poorly designed interview question. Its a blog post as well, not the format that would be presented to a candidate.

I think it has clear requirements and opportunities for nudges from the interviewer without invalidating the assessment (when someone inevitably gets tunnel vision on one particular requirement). It has plenty of ways for an interviewee to demonstrate their knowledge and solve the problem in different ways.

Ive run debounce interview questions that attempt to exercise similar competency from candidates, with layering on of requirements time allowing (leading/trailing edge, cancel, etc) and this queue form honestly feels closer to what Id expect devs to actually have built in their day to day.

aidos• 1 year ago

I feel similarly and again.

We actually have this pattern in our codebase and, while we don’t have all the features on top, it’s a succinct enough thing to understand that also gives lots of opportunity for discussion.

michaelsalim• 1 year ago

Same here. I thought that this specific problem is not that uncommon. On top of my mind: say if the endpoint you're hitting is rate-limited. It doesn't even have to be an API call. I think I've probably written something with the same pattern once or twice before.

I do agree that this is quite javascript specific though.

reillyse4• 1 year ago

If it’s rate limited it’s handling the concurrency for you. Just back off from the rate limit.

MatthiasPortzel• 1 year ago

I could write a solution to this pretty quickly, I’m very comfortable with callbacks in JavaScript and I’ve had to implement debouncing before. But this interviewer would then disqualify me for not using AI to write it for me. So I don’t understand what the interviewer is looking for.

ncann• 1 year ago

Here's a naive, faulty implementation

For this first implementation, I don't see anything ever added to the queue. Am I missing something? New task is added to the queue if the queue is not empty only, but when the queue is empty the task is executed and the queue remains empty so in the end the queue is always empty?

JohnKemeny• 1 year ago

That's how I read it too. Nothing is ever added.

Arch-TK• 1 year ago

That's correct.

63stack2• 1 year ago

Another thing is that the article emphasized that it's single threaded. That by itself guarantees that there will only ever be 1 inflight request, since calling the send() function will block until the request completes, and the callback is called.

If there is some kind of cooperative multitasking going on, then it should be noted in the pseudo code with eg. async/await or equivalent keywords. As the code is, send() never gives back control to the calling code, until it completely finishes.

_benton2• 1 year ago

JS has an event loop, it's single threaded but still lets you write asynchronous code.

let send = (payload, callback) => fetch(...).then(callback)

fetch() returns a promise synchronously, but it's not awaited.

gpderetta• 1 year ago

it is too abstract to say for sure, but send might just block until the request is handled off to the next layer (for example succesfully written to the OS network socket buffer), so unless the server carefully closes its recv window until it is done handling the request[1] , no, I wouldn't expect send to block until the server is done handling the request.

[1] i.e. backpressure, which would actually be the ideal way for the server to implement whatever rate limiting it wants, but we are assuming here that the server has a less than ideal interface.

rehevkor52• 1 year ago

Yeah that confused me at first too. They seem to be treating send() as if it has the same behavior as a setTimeout() call. If you think of it that way, it starts to make sense.

ethan_smith• 1 year ago

You're absolutely right - the naive implementation has a logical flaw where the queue would always remain empty since tasks are only added when the queue is non-empty, creating a catch-22 situation where the queue can never grow.

bluelightning2k• 1 year ago

Interestingly I think I would over-think this. The interviewer is assuming a single server, running in a VPS type environment. There's also no notion of state persistence/timeout/recovery etc. I think I'd immediately have started factoring those things in.

ALSO while JavaScript is a single threaded environment, the while solution would still basically work due to the scheduler (at least if you yield, await sleep, etc.)

jnettome• 1 year ago

thanks for sharing and by reading the blogpost and the comments I think I get the whole point: it's all about how engineers understand the requests and the reasoning about how does it approach that more than the code itself. If this raw code really works or not it's almost secondary here - IMHO nobody I'll start coding a real queue out of blue like this.

comrade1234• 1 year ago

Do I have to use JavaScript? I'd write it in Java in a way that it would be trivial to ramp up the number of connections in the pool once they fix their stupid server.

4ndrewl2• 1 year ago

Definitely one of those where the interviewer wants to show how smart they are.

IdontKnowRust• 1 year ago

Oh I see what you're doing here...this is just an interview to massage the interviewer's ego.

It must be so boring working you

fastball6• 1 year ago

How does this interview question massage the interviewer's ego?

thedude14• 1 year ago

As a self promoting post I think the author did a good job. As an interview format, I would rather work somewhere less ego driven development and more real problem oriented workplace. But that is just me. Someone could prefer these kind of interviews. I also did a set of questions for java engineers in the past and I always felt there is something really icky. I also noticed the engineers with huge ego revel in these kind of candidate assessments as it makes the feel good, but the candidate performance is poorly tested. Thats what the probation period is for. Just ask the candidate whats his experience. Asking these "cleverly" designed problems is nice for the interviever importance of keeping his job, but is not really usefull. You could even miss a good engineer. Perhaps i see this too narrow and you just really want to observe what the candidate is thinking, but you could make a couple of not really complicated questions and you could see where he is at. I dont bite this head-game at all.

lubujackson• 1 year ago

I agree to a point. For me, what chaffs is the convulted prompt that goes against all my instincts for how to design something simply and clearly.

"Ok, but if you had to code something convulted and illogical..." I tend to have trouble with these sorts of black box problems not because of the challenge but because of going down the path feels wrong I would expect my day to day at the company would be surrounded by too clever solutions.

Also, recognize a minimum requirement to solve this under interview pressure is a lot of low-level futzing with Javascript async and timeout details. Not everyone comes in with that knowledge or experience, and it's fine if that is a hard requirement but it seems ancillary to the goal of "interviewing engineers". I can't imagine anyone solving this or even knowing how to prompt AI in the right ways without a fair bit of prior knowledge.

GeoAtreides2• 1 year ago

and more real problem oriented workplace

I literally had to implement this exact queue mechanism because of a 3rd party integration with an uncooperative server

it's a pretty real problem

dawnerd• 1 year ago

I’ve had to do a variation of this many times, not because the server necessarily could only handle one at a time but simply down to rate limits.

skydhash• 1 year ago

Did you have to do this within 30-60 minutes? Or was it some days long research followed by experimentation and testing (at least the first time)?

lordnacho• 1 year ago

The explanation is way too long, in an area that is pretty big and can be done in many ways. Couple this with candidates who will variously be fearful of asking to many or too few questions, and you just have confusion about who is good and who is not.

nothrabannosir• 1 year ago

for the record (and disregarding how appropriate this is as an interview question): in JS you can (ab)use the event loop and promise chains to do this for you without managing any queues or lists manually. You have a single `let job = Promise.success();` as a global var, and scheduling a new job becomes `job = job.then(f, errHandler).then(callback, errHandler)`. It's a nightmare to debug (because you can't "see" the in-process queue) but it means you don't have to muck around with manual lists, queues, loops, shift/unshift, "isProcessing" flags etc, all of which is basically you reimplementing that native functionality in user space. It completely sidesteps the bug of TFAs naive implementation.

Not advocating for this in prod but in the context of a programming puzzle it can be neat.

late edit: ironically this is also a comment on the LLM talk in TFA: messing with the event loop like this can give you a strong mental model of JS semantics. Using LLMs I would just have accepted a loop and never learned about promise chains. This is the risk in using LLMs: you plateau. If you will allow a tortured metaphor: my naive understanding of SR is that you always move at light speed, but in 4 dimensions, so the faster you move in the 3D world, the slower you move through time, and vice versa. Skill is similar: your skill vector is always a fixed size (= "talent"?). If you use LLMs, it's basically flat: complete tasks fast but learn nothing. Without them, you move diagonally upwards: always improving, but slower in the "task completion" plane. Are you ready to plateau?

odo1242• 1 year ago

Honestly that’s not even an abuse of the event loop / Promises. Making a queue like this is literally one of the intended uses of Promises.

bmacho• 1 year ago

If you don't care about the order of requests then you can just set up a flag to denote if a task is running, and keep rescheduling the other tasks. Something like

      let isProcessing = false;

      async function checkFlagAndRun(task) {
          if (isProcessing) {
              return setTimeout(() => checkFlagAndRun(task), 0);
          }

          isProcessing = true;
          await task();
          isProcessing = false;
      }

should do the trick. You can test it with

      function delayedLog(message, delay) {
          return new Promise(resolve => {
              setTimeout(() => {
                  console.log(message);
                  resolve();
              }, delay);
          });
      }

      function test(name,num) {
          for (let i = 1; i <= num; i++) {
              const delay = Math.floor(Math.random() * 1000 + 1);
              checkFlagAndRun(() => delayedLog(`${name}-${i} waited ${delay} ms`, delay));
          }
      }

      test('t1',20); test('t2',20); test('t3',20);

BTW, for 4 scheduled tasks, it basically always keeps the order, and I am not sure why. Even if the first task always runs first, the rest 3 should race each other. 5 simultaneously scheduled tasks ruins the order.

jonchurch_3• 1 year ago

Nesting at 5 deep increases the timeouts to 4ms! TIL

https://developer.mozilla.org/en-US/docs/Web/API/Window/setT...

remram• 1 year ago

I expected this to be the answer. I guess the interview is not necessarily for JavaScript programmers, but this seems like the correct solution. It brings in some facilities for dealing with errors, too.

Jarwain3• 1 year ago

I tried this at work but ran into issues where if the server had some error or issue or took longer than expected, the job queue grew too large and caused OOM issues. I had to turn it into a manual list in order to debug the problem, though.

Plus we have a case where a certain type of request should skip to the front of the queue.

Leaning on promises does cut out a lot of the user space complication though.

brettgriffin• 1 year ago

I'm not going to dive into the specifics of my thoughts on this question. I think a lot of comments here address this.

But does anyone else get embarrassed of their career choice when you read things like this?

I've loved software since I was a kid, but as I get older, and my friends' careers develop in private equity, medicine, law, {basically anything else}, I can tell a distinct difference between their field and mine. Like, there's no way a grown adult in another field evaluates another grown adult in the equivalent mechanism of what we see here. I know this as a fact.

I just saw a comment last week of a guy who proudly serves millions of webpages off a CSV-powered database, citing only reasons that were also covered by literally any other database.

It just doesn't feel like this is right.

brunooliv• 1 year ago

Agreed, this is just terrible for the field as a whole it’s like we’re regressing or something

joquarky3• 1 year ago

When I started writing code for a living 30 years ago, we were mostly left alone to solve problems.

Now it feels like I'm back in high school, including strict irrelevant rules to be followed, people constantly checking in on you, and especially all of the petty drama and popularity contests.

esafak• 1 year ago

Which part, the fact that you have to answer such questions to get a job? Those other fields are more established and have formal barriers to entry.

ThrowawayR2• 1 year ago

Lawyers have law school after a degree, a bar exam, legal liability for malpractice, and ongoing licensing requirements.

Medicine has medical school after a degree, a 5+ year residency under close supervision with significant failure rates, legal liability for malpractice, and ongoing licensing requirements.

So explain to us what it is that you "know this for a fact" regarding how they have it easier. Most of the people reading this, myself included, would never have been allowed into this industry, let alone been allowed to stay in it, if the bar were as high as law or medicine.

tkiolp4• 1 year ago

The difference is that if you fail medicine, it’s ok (it’s hard). But if you fail to get a job because of the stupid “async queue” author’s problem, well, that’s depressing.

glitchc4• 1 year ago

Perhaps the bar should be as high as law and medicine if we want people to take our industry just as seriously.

zaphirplane• 1 year ago

to put it another way there isn’t this much focus on show me you know this weird problem that I’ve been studying for 5 years as well me, your 5 min timer starts now

osigurdson3• 1 year ago

Many people in software have passed through similarly hard gates in the past. An engineering degree is harder to attain than a law degree for instance. The question isn't about these gates, it is about the interview practice once one is already through. Do law or medical interviews include questions unrelated to the work that they do in a reasonably analogous manner to leetcode? Maybe they do. Perhaps hiring is broken in all fields.

no_wizard10• 1 year ago

I know its not a popular opinion here or elsewhere, but since these interviews are so standard, why don't we have a uniform standard body where I can get a licensure, do yearly trainings etc as a software engineer? It would solve the same problem something like the CPA exam does.

bravesoul23• 1 year ago

Oh yeah. Spoke quite a bit to a doctor who wanted to get into a speciality last year. That shits hard. Intersection of mentally hard, hours demanding and high bars to entry.

We have it cushy. Really cushy. Unless you are working for a 2025 AI startup that works and pays you like a mule and uses the word mission unironically.

chis• 1 year ago

I think a lot of fields of engineering have analogous questions actually. EEs ask to explain a circuit or draw a new one. Mech Es ask to design some piece of simple hardware with a clever catch. Interviewing is just hard, it’s impossible to cover breadth of knowledge in 45 mins so we end up with little brain teasers.

This particular question is a bit ill formed and confusing I will say. But that might serve as a nice signal to the candidate that they should work elsewhere, so not all is lost.

trhway2• 1 year ago

The higher layer of people in our industry aren’t subjected to those questions. They are evaluated and get jobs more like in law and medicine, ie based on connections and track of record.

Me and you are just not of that high layer. We’re kind of laborers given those simple aptitude tests.

When I was on track to get into the higher layer 15 years ago I got that my last job just by invitation and half an hour talk with VP. Next offer and other invitations came soon the same way, yet I got lazy and stuck at the current job simplemindedly digging the trench deeper and deeper like a laborer.

lmm7• 1 year ago

does anyone else get embarrassed of their career choice when you read things like this?

On the contrary, it makes me proud. In private equity, medicine, or law, if you have the right accent and went to a good school and have some good names on your resume, you can get a job even if you're thoroughly incompetent - and if you're a genius but don't have the right credentials you'll probably be overlooked. In programming it still mostly comes down to whether you can actually program. Long may it continue.

anon_e-moose5• 1 year ago

Leetcode has nothing to do with actually programming a project that lives long enough to deliver value.

coherentpony2• 1 year ago

It just doesn't feel like this is right.

I know the feeling.

The author says this is one of their favourite interview questions. I stop to wonder what the others are.

When I'm interviewing a candidate, I'm trying to assess really a few things: 1) the capability of the person I'm interviewing to have a technical conversation with another human being; 2) how this person thinks when they are presented with a problem they have to solve; and 3) can this person be trusted with important work?

For 1) and 2), coding interviews and the types of artificially constructed and unrealistic scenarios really aren't helpful, in my experience. I care a lot less about the person being able to solve one specific problem I hand them and I care a lot more about the person being able to handle a much more realistic scenario of being hand handed an ill-defined thing and picking it apart. Those conversations are typically much more open-ended; the goal is to hear how the person approaches the problem, what assumptions they make about the problem, and what follow-ups are needed once they realise at least one of their assumptions is wrong.

This is a really hard thing to do. For example, I imagine (but do not know) that when a medical practice hires a doctor for a certain role, there is an expectation that they already know how the human body works. For an ER doctor, you might care more about how well that person can prioritise and triage patients based on their initial symptoms. And you might also care about how that person handles an escalation when a patient presents not too awfully but is in fact seriously ill. For a GP, it's probably more important for a practice to care more about healthcare philosophy and patient care approaches rather than the prioritisation thing I mentioned above. I'm spit-balling here, but the point is these two situations are both hiring doctors. You care less about what the person knows because there is a tacit assumption that they know what they need to know; you're not giving the candidate a trial surgery or differential diagnosis (maybe... again I'm not a doctor so I don't actually know what I'm talking about here).

If I'm hiring a software engineer or performance engineer, I am trying to figure out how you approach a software design problem or a performance problem. I am not trying to figure out if you can design an async queue in a single-threaded client. This problem doesn't even generalise well to a real situation. It would be like asking a doctor to assume that a patient has no allergies.

Item number 3) is "Can this person be trusted with important work?" and this is basically impossible to determine from an interview. It's also impossible to determine from a CV. The only way to find out is to hire them and give them important work. CVs will say that a candidate was responsible for X, Y and Z. They never say what their contribution was, or whether or not that contribution was a group effort or solo. The only way to find out, is to hire. And I've hired candidates that I thought could be trusted and I was wrong. It sucks. You course-correct them and figure out how to get them to a place where they can be trusted.

Hiring is hard. It's a massive risk. Interviews only give you a partial picture. When you get a good hire it's such a blessing and reduces my anxiety. When you hire a candidate you thought would be good and turns out to be an absolute pain to manage it causes me many sleepless nights.

hobs3• 1 year ago

My favorite interviews I have taken:

* Give us a presentation about a meaningful amount of work you did at a company (no NDA violations of course) and spend at least an hour talking about what you did, how you did it, what went well and what did not, and then be prepared for questions.

* Actual software development issues that the team sees every day (not hard mode, just normal) submitted as a PR - review it thoroughly.

* Given a running code environment, fix a bug (you have a debugger, full ide, and an hour to look at it) - not so much about the end result as seeing how you work and your process.

000ooo000• 1 year ago

It's because our profession seems to attract a number of intellectually insecure people who thrive on these little puzzles and the associated minutiae as a means of feeling a sense of superiority. They all think they've figured it out: the best way to tell if someone is a Good Dev or a Shit Dev. Of course, administering the test, there's no way they could possibly be anything but the Good Dev. It is embarrassing. Don't believe me? Why can't they help but blog about it?

throwaway20377• 1 year ago

The real problem: How you accurately evaluate a candidate without these questions? I dislike them as much as the next person, but I don't know a better way. Literally, all the best tech firms and ibanks do it. They pay the most and are most profitable. They must be doing something right. The real trick is finding a "fractically complex" question with many levels. The one in this blog is pretty good! No candidate can solve it perfectly in the allotted time, but you can have a good discussion about the "edges" of the problem -- where good candidates shine.

renegade-otter• 1 year ago

We have FAANG to thank for this. They pioneer counterproductive interview questions (remember puzzles?), and the industry just copies these trends, like zombies.

Then what happens is these Leetcode heroes, never having built anything from scratch in their lives, create a hazing ritual for new candidates.

What is the point of, say, a system design interview asking to design a planet-scale system when most people never came close to one or, again, never built one because they are just out of school?

And, yes, I know - "how would you interview a recent student?".

Fine, I was a student in 2004, so why are we having the same goddamned test?

throwaway20377• 1 year ago

I heard that private equity does the equivalent. They show you balance sheet of a potential takeover candidate then ask for feedback. I assume that good candidates will need to do some Excel to answer their questions. Also, interviewing for trader roles at ibanks is similar. Show a trading scenario, ask what they would do and why. I guess law must be similar as well.

no_wizard10• 1 year ago

The difference to me is this: they're real analyst questions that you will have likely dealt with before in some detail, and not an obscure algorithm I maybe haven't seen since college or a leetcode not particularly real world presented or relevant brain teaser.

They're things you actually do, and I imagine most people applying to these roles have done, either in exercise (say in college) or in previous jobs. Its still a practical assessment.

Where software interviewing is different is the assessments aren't grounded in being all that practical

anon12512• 1 year ago

Don't know how many experience you get but other fields have a lot of these. Accountance have certificates, finance / quant have to solve headmaths type of problems.

saagarjha8• 1 year ago

I had lunch with a friend who was trying to get a job at a law firm and they told me that their interview was just vibes and if they asked him actual law questions it would be refreshing. So maybe things aren't necessarily greener on the other side?

weego• 1 year ago

They build teams in their own broken image of what a good programmer should be, and then get to manager and director and mould entire companies the same way.

They become hotbeds of intellectually rich but functionally and productively inept individuals who value spending resources indulging in esoteric side quests instead of driving businesses forwards in ways that are 'just sustainable enough'.

I've always been on the periphery of FAANG 'level' situations trying to focus on the surface where tech and humans meet and as the 3 decades of my career have gone on, software engineering has become more and more ludicrous and bubble like to the point where it, and the developers working on it, are now just the annoyance between me and my goals.

higeorge133• 1 year ago

Of course it's not right. Let's be honest, our profession is in the era where software engineer = factory worker, and the worst part is that we have been playing music chairs right for the last couple years. So yeah all these professions have some steady status/wealth/qol progression and upgrade while people gain years of experience, while in software development it doesn't matter how many years of experience we have, which companies we worked on, their sector, whether your company is using the saas we were working on, etc.; we are going to get judged by trivia questions and leetcode.

rockostrich• 1 year ago

Other fields definitely involve similar lines of questioning in interviews. Medicine and law are special cases because they have their own set of standards that must be passed before you can even get an interview, but private equity interviews definitely include case studies/technical questions in a similar vein to the one shared in this post.

Twirrim2• 1 year ago

I used to give a code review task, of some particularly egregious python code. I'd provide all help with the syntax, and emphasise strongly upfront I don't expect them to know python or its syntax. It has proven to be a low stress task for candidates. They're not trying to solve a brain teaser, they're just doing something that's going to be part of the job. Reading code, understanding what it is doing, and providing feedback to make it more maintainable.

When all around me in this FAANG type role are engineers giving leet code esque questions, I was trying to be a breath of fresh air for them.

Sadly, I need to rethink this now, because you can throw it in an LLM and it'll give you a nearly complete answer. I've already had one candidate clearly do that.

actinium226• 1 year ago

The most "refreshing" interview I had was one where the guy had a list of like 100 questions about C++, and he would just go through and ask "do you know what SIMD is?" or "are you familiar with smart pointers?" or "tell me about templates" (most were less open ended than the template one). If I responded yes, he'd follow up, and it was more of a discussion. If I said no he'd just move on to the next one (sometimes I'd ask what it was and he'd explain).

At one company I lobbied hard against standardizing our interview on a question designed to test the candidate's multi-threaded knowledge. I insisted that if we needed multithreading, we could just ask the candidate, and ask them to elaborate. Fortunately I won that little battle.

Sometimes in interviews you get tunnel vision and you can't see the forest through the trees, and you don't realize that the interviewer is asking you about multithreading because they're being coy. That's the kind of shitty interview we need to avoid, because it leads to the false conclusion that the candidate doesn't know about multithreading when actually you just don't know how to ask.

quietbritishjim2• 1 year ago

But does anyone else get embarrassed of their career choice when you read things like this?

What specifically is embarrassing about it? None of these questions seem especially hard, and they're exactly the sort of problem that I face on a daily basis in my work. They're also fairly discussion based rather than having one silly trick answer (like the XOR trick that came up recently here). The whole point of an interview is to check that the candidate can do their job. What would you propose instead? We don't bother to interview and just cross our fingers and blindly hope they'll know what they're doing?

I can only assume that the real reason for your objection is that your job actually doesn't involve solving problems like these ones. Well, that's fair enough, and then I'd expect the interview for your position to look different. But why would you assume that there are no jobs that really need these skills?

Your comment about using a CSV file for a database seems unrelated. Maybe I missed the real point of your comment?

anon_e-moose5• 1 year ago

None of these questions seem especially hard, and they're exactly the sort of problem that I face on a daily basis in my work.

Really? Do you invert linked lists all day? When the last time you had to traverse a binary tree? Genuine questions. I'm sure there has to be a mismatch between what we define as "those questions".

They're also fairly discussion based

They're also performed wildly differently with no standards at all. I've had good coding interviews with the coding as a starting point for a conversation. But I've also had it super strict on rails, interviewer silent and just expecting you to one-shot the optimal path. The latter is particularly great at hiring professional interviewers rather than actual professionals at the job.

morsecodist• 1 year ago

Not really. These other industries are evaluating people somehow. Whether it's vibes, connections, resume, or some sort of technical evaluation you'll have a grown adult evaluating you. Hiring will always feel a bit lame and arbitrary, you have limited time and information to pick someone. You're not going to be able to understand candidates fully and you'll probably pick wrong a fair bit. So we come up with criteria that's a bit arbitrary but you need at least some effort and smarts to meet them so it's at least a bit correlated with a good hire. I don't think the non technical methods are any more or less dignified.

mdavid626• 1 year ago

SW engineering is rather young, compared to others, like construction, medicine, law, etc. It doesn’t have good established patterns, which is followed by everyone.

DavidWoof• 1 year ago

I think the "sendOnce" question is fine. Software development is just different than other professions, and you get a lot of candidates who talk a good show but can't actually program at all. For a decent dev, this isn't programming, it's typing.

But all the "ok, now add this feature..." stuff is just a sign that the interviewer is an insecure asshole. And you get insecure asshole interviewers in other professions as well, asking about obscure laws or diagnoses.

Software is still a bit of a craft, and it's perfectly reasonable to ask a job seeker on a construction site to go hammer a nail. But nobody is going to follow that up with a bunch of "OK, now do an L-joint" just to show off their own knowledge.

prats226• 1 year ago

Isn't it because there is a difference in your field and other fields?

1) Scope - Other fields like law, medicine atleast are impacting one unit at a time, vs software which is impacting large number of users through your work. I am sure research interviews will go through similar process?

2) Feedback - Just basis past work, you would get a good sense of their aptitude. Very hard to do it in programming without you spending a lot of time going through their work?

3) Subjectivity - Wrt coding, very good way to get objective output in interview by getting other person to write code, can't do that in medicine for example?

bravesoul23• 1 year ago

I had a favourite interview question when I was 3 years in. My boss tempered my enthusiasm by letting me ask it but made it not a requirement to be hired so more of a bonus "extension question". Glad they did that. I was being rediculous. I assumed "anyone who used this framework must have come across this problem" but was just an assumption.

MichaelRo2• 1 year ago

Well, that's because in law, you can't attend a 4 week bootcamp, call yourself a lawyer and inflate the ranks of desperate looking for a job. Now, also remote.

And as a doctor, you can't attend a 4 week bootcamp, call yourself a doctor and inflate the ranks of desperate looking for a job. And at least you gotta be in person, no remote.

Much of the problems of software engineering stem from the highly inflationary nature of it's people. There's a trillion of us already and more keep coming. That's what you get when there's a dozen for everything: a dime's worth.

cdaringe• 1 year ago

But does anyone else get embarrassed

No.

there's no way a grown adult in another field evaluates another grown adult …

There is. Demonstrating competency over a common and interesting problem is the baseline.

Are queues commonly needed? Yes. Is task processing commonly async? Yes.

Fantastic, then what precisely is the problem?

What is most puzzling to me is that people are confounded when even low standards are set for each other. This isn’t a high bar.

red-iron-pine• 1 year ago

there are formal regulatory boards for most of this. Lawyers gotta pass the bar, medical folks have their own board exams, finance has things like CPA or CFP certifications, etc.

Most Mechanical / Electrical / Civil Engineers have formal accreditation processes, too.

IT is something of a clusterfuck but even there we have things like CCIE or RHEL or Windows Certs that can prove a minimum level of competency.

The lack of regulation makes it easy for anyone to be a dev but also means there is no formal minimum standard.

rubyn00bie• 1 year ago

I’m really confused why this is an “async queue.” Seems pretty synchronous to me since requests are completed in order, one at a time. I literally wrote something to do this in the past few months. This was to work around JavaScript’s asynchronous IO making a shit show of updates from library being used in the client. I had to queue requests in JavaScript, have them execute in order (FIFO), and explicitly described it “synchronous.”

Is it only “async” because it’s doing it in JavaScript and the underlying network request API is asynchronous? Seems like, IMHO, a really bad way to describe the desired result since all IO in JavaScript is going to be async by default.

8note3• 1 year ago

the async part isnt very exciting, but its the callback after the entry has been through the queue and worked on.

its certainly serialized, but nothing fancy otherwise.

it would be synchronous if you blocked the requester until the request go through the queue and then completed. you wouldnt need to introduce an async/await.

you can see examples in JS on the node FS functions. the defualt ones are async, but they have some magic wrappers that make it actually sychronous and block the event loop from running until the file is loaded

dakiol3• 1 year ago

I don’t know anything about the author, so just speculating here: assuming that the interview lasts 1h, it’s not realistic (nor fair) to judge the candidate’s answer if the interviewer has spent more than 1h to think about the problem and potential solution(s).

Interviewers have thought about the problem they propose countless of times (at least once per interview they have hold) each time refines their understanding of the problem, and so they become god of their tiny realm. Candidates have less than one hour, add to that stress and a single shot to get it more or less right. You’re not assessing candidate’s ability to code nor their ability to handle new requirements as they come.

fastball6• 1 year ago

So do you want to give candidates infinite time (which they won't have on-the-job) or not attempt to assess their coding ability or what?

saagarjha8• 1 year ago

I spend more time than my interviewees on the question to try to solve the problem every way that it is possible to solve it. If a candidate picks any of the solutions they pass. If they pick a solution I didn't know of they also pass (with flying colors) but I fail.

dakiol3• 1 year ago

Here’s an idea for fair interviews:

Interviewer and candidate meet at time X for 1h session of “live coding”. A saas throws at them both one problem at random. Let the game begin. The company can decide if they want interviewer and candidate to collaborate together to solve the problem (the saas is the judge) or perhaps they both need to play against each other and see who gets the optimal solution.

You can add a twist (faangs most likely): if the candidate submits a “better” answer than the interviewer’s , candidate takes over their job.

An LLM could be very well behind the saas.

Oh boy, I wouldn’t feel that nervous anymore in any interview. Fairness is the trick. One feels so underpowered when you know that the interviewer knows every detail about the proposed problem. But when both have no idea about the problem? That’s levelling the field!

billforsternz• 1 year ago

if the candidate submits a “better” answer than the interviewer’s , candidate takes over their job

Corporate life meets the squid games (I quite like it:)

glitchc4• 1 year ago

Why would anyone agree to participate in interviews then? Do we then force developers to conduct interviews? If so, which ones? The superstars or the ones on PIP? You can see where this is going..

tengbretson• 1 year ago

I guess think of it as a promotion/relegation league system, except you get relegated to the "unemployeed" league.

yoz-y• 1 year ago

Might be a whoosh, but really don’t understand the idea of seeing the interviewer as an adversary. Stress in interviews comes from many places but honestly one of the roles of the interviewer is to bring it down.

ameliaquining2• 1 year ago

I think maybe the problem being alluded to is that a lot of interviewers aren't that good at this and instead give off vibes that play up the "I'm judging you from a default presumption that I'm more competent than you" angle.

(Really, it shouldn't be surprising that most technical interviewers aren't that competent, since they usually aren't selected for it.)

koakuma-chan• 1 year ago

In another thread I asked if leetcode style questions are still common, and the answer I got was yes, so where would I encounter this kind of question? I only ever got leetcode style questions or something like "what is the difference between var and let"

relativeadv• 1 year ago

"This is a good way to test how "AI-native" the candidate is."

yuck

sbstp• 1 year ago

yuck.

ykonstant2• 1 year ago

In a world of AI-natives, be an AI-drunken-British-football-fan-tourist.

ww5202• 1 year ago

If I were asked this question, the first thing I said would be this is a poorly designed architecture. Client is the poor place to do throttling by itself. It has no information on the aggregated load of the system. It makes assumption that leads to complicate code in the sample code. There're more robust and better ways to do flow control and throttling.

8note3• 1 year ago

the intro isnt throttling, its request serialization. there isnt some limit to keep your requests to, just that its one at a time. it could go as fast or as slow as the individual requests finish.

its still not a great architecture, but its different from throttling

ww5202• 1 year ago

But that server is faulty!! If it has to handle multiple requests at once, it starts to break down. So, we decide to make our server's life easier by trying to ensure, from the client, that it doesn't ever have to handle more than one request at once

wonnage• 1 year ago

The minDelay extension feels contrived and also the solution sucks. None of the pending requests are actually added to the queue until the timeout is finished, meaning you have no knowledge of all these delayed requests until the timeout passes and they all enqueue themselves

evil-olive• 1 year ago

echoing the other comments about this being a rather terrible interview question...

this interview can be given in JavaScript or any other language

it's a language-agnostic question...but it revolves around the assumption of making a callback on request completion. which is common in JS, but if you were solving this in some other language, that's usually not idiomatic at all.

followed by:

For candidates without JavaScript experience or doing this interview in pseudo-code, you have to tell them that there's another function available to them now with the following signature:
declare function setTimeout(callback: () => void, delayMs: number): number;

so you add in this curveball of delaying requests (it's unclear why?), and it's trivial to solve...using a function from the JS stdlib. and if the candidate is not using JS, you need to tell them "oh there's a function from JS that you can assume is available"

After sendOnce is implemented, it's time to make the interview a lot more interesting. This is where you can start to distinguish less skilled software engineers from more skilled software engineers. You can do this by adding a bunch of new requirements to the problem

as you originally specified it, this code is a workaround for a buggy server. and for Contrived Interview Reasons we can't modify the server at all, only the client.

in that scenario, "extend it into a generic queue with a bunch of bells and whistles" is maybe the worst design decision you could pursue? this thing, if it existed in the real world, should be named something like SingleRequestQueueForWorkingAroundHopelesslyBuggyServer with comments explaining the backstory for why it needs to exist. working around the hopelessly buggy server should be roped off into one small corner of the codebase, and not allowed to infect other code that makes normal requests to non-buggy servers.

resonious2• 1 year ago

I dunno about you, but I spend a good amount of time writing my way around buggy servers that I can't change. It seems pretty realistic to me.

rustystump• 1 year ago

I think we all have but that doesn't change that this is almost exclusively a js specific interview question with a very js'y solution to the point of hammering in a imagined "js land" api.

I am not against testing deeper language understanding for a job that requires it but the layers of contrivances to make it "not only js" rightfully rubs non-js devs the wrong way. This comes from someone who loves them some js.

The AI ick at the end makes what would have been mildly interesting, incoherent and uninteresting.

didip• 1 year ago

The use-case described is ill suited to be addressed by the client.

Which make the whole coding exercise moot.

What if there are 1 million users opening the browser at the same time?

The queue question is fun but doing it in the client is not right.

resonious2• 1 year ago

This might be a server interacting with another server.

fastball6• 1 year ago

This is addressed in the article.

So, we decide to make our server's life easier by trying to ensure, from the client, that it doesn't ever have to handle more than one request at once (at least from the same client, so we can assume this is a single-server per-client type of architecture).

cdrini• 1 year ago

Yeah I think the premise is a bit poorly designed, I would just wave it away and focus on the queue. The coding problem itself is pretty well defined. And I think the premise is intentionally presented kind of poorly defined, which makes me think it's meant to not really be part of the problem.

neallindsay2• 1 year ago

Promises in JS make this stuff much easier (at least to my mind):

const lockify = f => {

  let lock = Promise.resolve()

  return (...args) => {

    const result = lock.then(() => f(...args))

    lock = result.catch(() => {})

    return result.then(v => v)

  }

}

fastball6• 1 year ago

Easier to write. But there is a case to be made that code which can be understood without understanding somewhat esoteric language internals is superior.

yeasku• 1 year ago

Is code wrote for a broken server.

It makes no sense even with common js idiom.

neallindsay2• 1 year ago

I guess "esoteric" is in the eye of the beholder, but Promises seem a lot easier than the old callback style we used to use for asynchronous operations.

jtchang• 1 year ago

Is the send function considered non-blocking?

isbvhodnvemrwvn2• 1 year ago

Why would it have a completion callback if it wasn't?

_benton2• 1 year ago

You can also schedule code to run each "tick" of the event loop, which is a non-blocking version of a while loop.

Or you could promisify the send function and use normal async/await.

   let q = Promise.resolve(),
     sendAsync = (p) => new Promise(r => send(p, r)),
     sendOnce = (p, c, ms) => setTimeout(_ => q.then(_ => sendAsync(p)).then(c), ms)

Or you could actually spin up a new worker thread and get multithreading :P

charleslmunger3• 1 year ago

I've implemented multiple production versions of this problem (but not in JavaScript)[1], so maybe my view of this problem is miscalibrated...

This feels both too easy and too hard for an interview? I would expect almost any new grad to be able to implement this in the language of their choice. Adding delays makes it less trivial, except that the answer is... Just use the function provided by the language. That's the right answer for real code, but what are you really assessing by asking it?

[1] https://github.com/google/guava/blob/master/guava/src/com/go...

fastball6• 1 year ago

You explained how it is too easy, so how is it also too hard?

charleslmunger3• 1 year ago

It's too hard because the variations you could add to it (multi threading) that add enough depth to make it hard make it too hard, in my opinion. If you look at the implementation I linked in my previous comment, it's fully lock-free, which is pretty unreasonable to expect from anyone who isn't already familiar with lock free concurrency. On the other hand the version with a lock is basically identical to the single thread version. Asking for the two-lock queue is also a bad interview question because it's not something you'd reasonably expect someone to derive in an interview.

The other examples given for fleshing it out are all pretty similar; if a candidate can do one, chances are they can do the others too. If you want to get a decent signal if candidate skill, you have to ask a question easy enough that any candidate you'd accept can answer it, then incrementally add difficulty until you've given the candidate a chance to show off the limit of their abilities (at least as applied to your question).

Otherwise you ask a too-easy question which everyone nails, then make it way too hard and everyone fails. Or you ask a too-easy question and follow it up with additional enhancements that don't actually add much difficulty, and again all the candidates look similar. That's just my experience; the author seems pleased with the question so maybe they're getting good signal out of it.

kazinator• 1 year ago

I did this in the firmware of a VoIP base station.

I was informed by the radio firmware guys that a certain kind of request from the host could not be handled concurrently by the radio module due to an unchecked conflict over some global piece of memory or whatever.

I create a wait-free circular buffer for serializing the requests of that type, where the replies from the previous request would kick down the next one.

No mutexes, only atomic compare-swap.

charleslmunger3• 1 year ago

How did you make it wait free with only compare and swap?

IgorPartola2• 1 year ago

It’s funny because I have had ti implement “serialized fetch()” a few times recently, with delays and random jitter too.

I think this question is a bit confusing in its wording even though the concept is actually quite useful in practice. First, async queues have nothing to do with network coms. You can have a async queues for local tasks.

Also while it is obvious to most that you shouldn’t do this, you can also satisfy the requirements to this task by polling the queue and flag using setTimeout() or setInterval(): on invocation, check if there is anything in the queue and if so, if we aren’t waiting on a response fire off the next send().

Retry logic with this system is always a problem. Do you block the queue forever by retrying a request that will never complete (which lets the queue grow infinite in size), or do you give up after some number of retired? If you give up, does that invalidate all queued requests? Some? None? This becomes application-specific. For this kind of thing I have implemented it using multiple parallel queues. That is, you request a send() but using a specifically named queue so that if one queue’s serialized requests break, other queues aren’t affected.

If you do something like `sendOnce(payloadA, callbackA, 5000); sendOnce(payloadB, callbackB, 1);` should payloadB be sent in 1ms or 5000 + RTT + 1ms?

You could solve this in the JavaScript environment by using something like WebSockets or WebTransport much more trivially than by using send() which is I assume a thinly veiled fetch(). This probably fails OP’s interview but in reality leverages the lower level queueing/buffering.

A more fun and likely more illuminating question would be to do something like provide a version of send() that uses a callback for the response and ask to convert it to a promise. This is a really fun one that I had to deal with when using WebCodecs: a video decoder uses callbacks to give you frames but for example Safari has a bug where it will return frames that are encoded as delta frames out of presentation order. So the much better API is to feed a bunch of demuxed encoded chunks to a wrapper around VideoDecoder, and then wait for the resolution (or rejection) of a promise where the result is all the decoded frames at once. This problem really gets at the concept of callbacks vs promises which I think is the right level of abstraction for evaluating how someone thinks of single threaded concurrency. You also can get a really good feel for a person’s attitude here if they refuse to use callbacks or promises (or the async/await sugar around promises).

bvrmn• 1 year ago

I don't understand what's tricky about converting callback-style to promise-style. Even writing a decorator is trivial.

IgorPartola2• 1 year ago

It’s not tricky if you understand how both work. If you don’t it will be a challenge, especially if you add all the correct error handling and cancelation. Bonus points if you make it work with only up to N tasks running at a time.

None of these interview questions are hard. They are just either domain specific (like callbacks/promises/async/await) or designed to trip you up on details.

nmca• 1 year ago

Why is the method called sendOnce? It’s send with a capacity limiter / semaphore right, so what about it is Once?

saagarjha8• 1 year ago

I think it really ought to be called "sendOneAtATime" but I assume the author just picked a bad name for it.

mgradowski• 1 year ago

I'm really confused because I had to scroll half the comment section for the word `semaphore`.

This seems to be an interview question about JS esoterica, not concurrent programming.

ayaros• 1 year ago

I made use of this in my LisaGUI project; I referenced an absolutely fantastic example on this on SO: https://stackoverflow.com/a/63208885

joquarky3• 1 year ago

I'd just have them play Factorio and watch how they reason.

ykonstant2• 1 year ago

Uh oh, I am horrible at Factorio ＼(〇_ｏ)／ But I am a mathematician, I wonder if that makes things better or worse... (•ิ_•ิ)?

SAI_Peregrinus• 1 year ago

I've seen somewhat similar things in embedded development, e.g. ADCs with a triggered conversion mode that start a new conversion on receipt of a new trigger, abandoning a previous conversion if one was in progress. They fire an interrupt when the conversion completes. Not in any way buggy or unexpected, ICs generally either can block or can immediately respond but can't queue multiple requests.

Of course on the embedded side you're likely using C, quite likely an RTOS and thus threads, but if you're just using a superloop then you've got a single-threaded system (though with the complication of interrupt handlers) a bit like the interview asks about. I'd probably use a state machine for this with a superloop design, just about everything "async" in embedded boils down to writing a state machine & polling it. Actually writing a fully general-purpose async queue for embedded systems is rather more work, because you'll have to consider how it can be used from within the interrupt context. You really shouldn't block in an interrupt context, so all the queue operations need to be non-blocking. That turns it into something far too complex for an interview question.

robertlagrant• 1 year ago

(a lot of people resort to some type of blocking sleep style function call to solve the delay part of this problem)

In many async languages you can do an async sleep (e.g. Python's asyncio.sleep()) which is a sleep that uses the event loop. Really, that's all Javascript's setTimeout() is doing anyway; it's just named differently.

andrewstuart2• 1 year ago

“Can you work out the tricks that require this previous experience? If you can then you’re smart if not then you’re worthless.”

Just say no thanks and walk out if this is their core way to assess your capabilities.

xg15• 1 year ago

The bug in this implementation is that if sendOnce is called consecutively and the previous request hasn't finished yet, then we violate the "one request at a time" requirement.

Maybe I haven't had enough coffee yet, but the "naive" implementation looks like it wouldn't use the queue at all, regardless how quickly or slowly you fire off the requests.

The code is literally

  if (requestQueue.length === 0) {
    ...
  }
  else {
    requestQueue.push(...)
  }

with no other push() anywhere else. So how would the queue ever get nonempty in the first place?

pavlov• 1 year ago

This interview starts off with the interviewer saying it's going to be in JavaScript, and then introducing a piece of code that's clearly not JavaScript:

  declare function send<P>(
    payload: P,
    callback: () => void
  ): void;

Doesn't inspire confidence in the interviewer's level of preparation.

ipnon• 1 year ago

As long as the candidate feels confused and the interviewer feels brilliant then all is well in the world.

diesal112• 1 year ago

Eh, the implementation is all Javascript and can be approached in any language. They're just providing function signatures with types so the candidate knows what they're working with.

Also the signatures are Typescript, which really isn't that far off in the context of an interview. Even in a pure JS codebase it's not uncommon for IDEs to pull the TS definitions of packages to provide basic type checking. But even pure JS libraries will normally provide typed signatures in their documentation.

If anything I'd say this shows that the interviewer is prepared, by ensuring the candidate has what they need to complete the question.

saagarjha8• 1 year ago

or any other language (even just pseudo-code)

jwmoz• 1 year ago

This is a complete nonsense. OP has invented a tricky technical test for themselves which they have spent long amounts of time thinking about.

In an interview a candidate is not in that mindset, at least I am not. Under stress and anxiety it is very difficult to fully understand things and build good cognitive structures in the mind.

vrighter• 1 year ago

Talk about javascript, present code in typescript. This would put me (the interviewee) off

bborud4• 1 year ago

If I were interviewed by someone presenting me with this task, I would spend a bit of time helping the interviewer clean up the problem and try to get to where they can explain what they want with just words. Clearly.

I’m not sure we’d necessarily get to the part where any kind of solution is proposed, but it would give me a lot of information about what kind of developer culture to expect at this company.

Just by how the problem is presented, I probably wouldn’t want to work for this company. Imagine having to work on real problems with people who demonstrate such poor problem formulation skills.

saagarjha8• 1 year ago

He gave you a function, its signature, and its context in the codebase. I don't really know what you are looking for to make it clearer.

bborud4• 1 year ago

I've conducted a fair number of interviews. At least one of the problems I pose to candidates are to test if they will ask questions that clarifies what I am asking for. Because being able to articulate both what you want to accomplish and what the non-negotiable constraints are, is a key skill. The more senior you are, the higher this part of the interview gets weighted.

This is also how a candidate can get to know the interviewer and possibly the company he is interviewing at. What does the interviewer say when you start picking apart what they are actually asking about.

The way this problem is posed has two main issues. The first is that it is unclear what the interviewer actually wants. The second is that the problem to be solved isn't well defined. This is later confirmed when we read the blog posting and it is revealed that rather than designing a solution to a problem, the interviewer expects the candidate to hack their way to a solution. Not to recognize what you are trying to accomplish and reason about how to solve such problems, but just peck at the problem. Mess with the code.

To make matters worse, it would appear that the interviewer is approaching the problem in a dubious manner -- solving a server problem by depending on the clients to cooperate. That should make you suspicious.

It gets further confused by adding poorly motivated extensions to the problem while misusing nomenclature. It appears he is asking for how to solve a difficult problem in messaging systems, but he isn't. He is asking for convenient ways to implement something much simpler. Which even makes me question if he would have recognized someone smarter than him misunderstanding and solving a harder problem -- someone who is capable of solving the kind of problems his use of nomenclature hints at, but apparently wasn't after.

Now, think about your reaction to this problem formulation from my perspective. From the perspective of someone who wants to hire senior developers. When I hire people I need people who can solve problems. Lacking that, I need someone I can train to solve problems. I have no need for people who dig themselves out of holes brute force. This is why some portion of my interview questions will only work if the candidate asks questions. Some of these interview questions are really easy to solve from a technical/algorithmic point of view, but only if you can identify the underlying problem.

If I had presented the problem as stated to a candidate and they did what the interviewer seemed to want, I'd probably have added them to the reject pile for lack of ability to take a step back and point out that this is a bit silly.

andrewstuart2• 1 year ago

> If I were interviewed by someone presenting me with this task, I would spend a bit of time helping the interviewer clean up the problem and try to get to where they can explain what they want with just words. Clearly

The interviewer would fail you because this interviewer wants to feel superior and more powerful. Your attempt to help them do better would enrage their sense that this interview must be putting them above you.

Their conclusion would be you are arrogant and hard to work with and you did not understand the simple problem that they explained and they would fail you.

All if that is clearly explained in the blog post, indirectly.

bborud4• 1 year ago

The interviewer would fail you because this interviewer wants to feel superior and more powerful

Not necessarily. The interviewer may only be insecure, inexperienced or not terribly good at conducting interviews. Of course, to the candidate this doesn't make much of a difference.

I'm not so sure this interviewer actually feels superior. I think he feels insecure. And with good reason.

saagarjha8• 1 year ago

Posting interview questions on Hacker News is so funny. Regardless of what the question is half the people will tell you that it's an interviewer ego trip that has no relevance to the real world while the other half will explain how interviews are actually a total waste of time and how carpenters do it right (obviously, without actually consulting how carpenters do their interviews). If the question has anything in it that's not an array then it's called "Leetcode" and clearly FAANG-engineer biased. If it has any other form then it's too confusing and too contrived. Of course, the end result of this discussion is that the author is a horrible employee at a horrible workplace and nobody should ever want to work with them. Thank god that 'randomuser123 was able to figure out that they were telling on themselves and explaining that if they were in this interview they'd stand up and tell the interviewer how their entire architecture was wrong and they should be ashamed for even asking the question instead of changing the world around them. And then everyone claps.

davidgomes2• 1 year ago

Phenomenal comment, thank you for writing it, made my day :)

gloosx5• 1 year ago

The proper implementation looks kinda bulky to me. Are you not allowed to use promises? Feels more like a naive solution for anyone who has few months of experience with javascript or is it cheating?

  const PromiseQueue = {
    queue: Promise.resolve(true),
    sendOnce(request) {
      return new Promise((resolve, reject) => {
        this.queue = this.queue
          .then(request)
          .then(resolve)
          .catch(reject)
      })
    }
  }

mohsen1• 1 year ago

Neat! and minimum delay can be done with Promise.race

mind-blight• 1 year ago

I actually tried to use this pattern to make an audio controller interface much nicer. If you get a long enough queue, you'll start to run into errors (I'm forgetting the exact message, but it was similar to a maximum recursion depth)

gloosx5• 1 year ago

This most likely happened because you had a queue operation which started another queue operation so a recursion was created which consumed every bit of memory it had available.

damidekronik• 1 year ago

And then once The Anyone gets few more years of experience they revert back to the bulky one.

gloosx5• 1 year ago

Dunno, every queue in every major library/project I saw is implemented like this. This is quite readable if you're familiar with js promises.

MrDarcy• 1 year ago

I believe you that this works, but I can’t easily read or comprehend it without considerable effort, so I’d grade it below a solution I could.

gloosx5• 1 year ago

If this is given in Javascript, I'd rate the promise solution higher since a Javascript job involves a ton of promisified async code like this. If this is given in C or pseudo-code, then for sure a good ol stack+flag+loop is looking good enough.

craftkiller2• 1 year ago

without considerable effort

Are you sure? I'm not a javascript programmer and it took less than 2 minutes to comprehend. If you think this takes considerable effort to comprehend then I don't think you actually tried.

dbetteridge• 1 year ago

Readability over brevity for maintainable code (I know an interview doesn't require this, but I look for it)

While this works, it's not exactly intuitive.

gloosx5• 1 year ago

In context of JS this kind of promisified async code is intuitive and this pattern is quite common in various projects and libraries, but the solution in C-like pseudocode of course looks more readable for general programming public.

a-priori• 1 year ago

You'll need to flatten the promise periodically if you use this approach, otherwise your performance will degrade a bit each time you enqueue something.

octo888• 1 year ago

As a general comment, I wish hiring managers found some other outlets for their enormous ego and insecurities than the process of hiring of software engineers.

I understand their argument that they have 1,000,000,000 applicants for every job so it's absolutely totally super required to be like. But companies still paying 2019 wages and are CRUD shops really need to bring it down a notch. You're getting a billion applicants because people are desperate and there are tons of CS grads, not because you're the greatest company on earth

ctvo• 1 year ago

You're getting a billion applicants because people are desperate and there are tons of CS grads, not because you're the greatest company on earth

How does this change the point? They would still like the best candidate out of that pool, not any warm body, since they have limited positions.

What is your approach to hiring and evaluating talent knowing the large number of applicants and how easy it is to _talk about software development_ vs. _actually developing software_, and how expensive and difficult it is to deal with a bad hire, even in America.

stevepotter3• 1 year ago

When I interview a candidate, I focus primarily on what they've done. Ideally they'd have a body of work online that I can view beforehand. Then I go through a high level system design and have a collaborative conversation. Last, I give a pretty straightforward coding question, whose purpose is only to make sure they aren't full of shit, which often they are.

The mistake I see interviewers make is that they are looking for the candidate to solve some kind of puzzle, and the focus is kept on whether they had that "ah-ha" moment vs a clean implementation. Maybe this would be a good approach for a job that required defusing a bomb, but this is relaxed desk work haha.

I once had someone bomb the coding, then email me a few hours after with a clean answer. One of the best hires I ever had.

kinow8• 1 year ago

I follow the dame process. I explain beforehand what kind of questions will be asked, and emphasize there are no tricky questions, that we are just curious about their experience, area of interest, preferences for designing ode, how they tackle ode quality and user support, etc.

Haven't had any major issues hiring this way, but I did reject people that appeared to be full-of as your said, or didn't have anything public on github/company gitlab/dockerhub/researchgate/etc.. With exceptions for entry level positions and a few that worked in research or govt where work couldn't be made public (they still normally have some participation in research publications, conferences, technotes, etc.)

quibono2• 1 year ago

didn't have anything public on github/company gitlab/dockerhub/researchgate/

What if the company GitLab/DockerHub instance is restricted and you can't get code samples (I think this is very common)? Or a different example: I have a few public repositories on GitHub but most of them are private - it seems like that's something you'd perceive negatively?

nobleach• 1 year ago

I did this once! I was given a "create Battleship" take-home assignment. Normally, I'd say, "yeah, I don't have time for this". But I happen to really like that game and had never thought of how to model it in code. So I took up the challenge. I spent time whiteboarding classes, interfaces, writing tests... in the end, I had a solid solution. I submitted my code and as I was doing so, I thought, "you know, this really could be handled by a couple of Set data structures. After hitting send, I did a quick follow-up with, "you know, this has a very simple solution" and typed some example code right in the body of the email. I love it when I can't just leave a problem alone. The hiring manager appreciated it too!

dekhn4• 1 year ago

Isn't it fun when you can take a game you play and write an implementation (both the game and the solver), thinking through all the details, and at the end, the solution is simple, elegant, and enlightening?

For many years I played Peg Solitaire, and after reading Norvig's AI:AMA, realized that Peg Solitaire was a fairly easy game to write a solver for. It wasn't that hard to write, but it turns out that I've only ever implemented recursion using function calls to implement a stack, rather than the iterative equivalent (using a python list as a stack, and a Set to save previously visited boards). Having the confidence of the working recursive version, and then reading up on iterative implementations, i was finally able to get a working iterative version (for some reason it's really unnatural-feeling to me) working.

jasonjmcghee• 1 year ago

I think it's a great idea to ask what someone might have done differently if they'd built one of those bodies of work professionally.

Priorities are often different with experiments and side projects.

I also think why someone built something can be more meaningful than how.

pak9rabid• 1 year ago

Coding is like sex, both are susceptible to performance anxiety when made to be done in front of others.

MathMonkeyMan• 1 year ago

It gets easier with practice.

heresie-dabord• 1 year ago

When I interview a candidate, I focus primarily on what they've done.

I like to hear candidates explain how they understood and met the customer's requirements. The code is only part of the success.

stevepotter3• 1 year ago

Agree, although this is often an undeveloped skill in newer folks. There are many other things I like to discuss in an interview: past mistakes, things they are especially proud of, times they trimmed scope to meet a deadline, working with difficult people, etc.

My goal for interviewing is to either hire the person, or not hire the person but have them walk away feeling like they got something out of our time together. Often I can quickly tell that the person isn't right for the role, in which case I will politely explain that to them and offer whatever advice I can.

donatj• 1 year ago

One of the best interview questions I ever received, I was asked to explain how something I liked worked in detail. Could be literally anything, just break it down step by step. I was told I could use the whiteboard but didn't have to.

I broke down a project I was particularly proud of drawing charts explaining internals.

It was clearly both a test of communication and reasoning skills, but it was frankly kind of fun to answer and put me at ease.

kinow8• 1 year ago

After some years applying for different positions, I started asking receuiters about their hiring process and straight out dropping out when there were technical tests like this.

Even when you nail the test, it is no guarantee you won't be just wasting your time.

I explain to the recruiter why I am turning down that opportunity and thank them.

Best jobs I had were mainly via my network of friends, or reaching out to engineers directly asking about their companies and open positions, then sharing CV and GitHub, then chatting about technologies used, bugs in production, and other past experiences.

MichaelRo2• 1 year ago

Well, I had an interview recently where I passed with flying honors the technical interview but they failed me at "cultural fit", which was strangely, the last one in the series.

Now I must say that I got the vibe from the start they weren't interested in hiring me as much as extracting proprietary quant / trading information from me, but I played along since I was also interested in their culture.

So at the final interview, I get a series of questions that basically The Senate asked Cosa Nostra in https://en.wikipedia.org/wiki/United_States_Senate_Special_C...

And foolish me, maybe, instead of taking the 5th Amendment "I respectfully decline to answer on the grounds that my answer may tend to incriminate me", I foolishly (did I say that again), gave a straight answer. From that on it was only downfall. Watch this movie, it's insightful: https://www.youtube.com/watch?v=TXdC293horg

When you interview, remember, HR and hiring manager are fucking pigs. Anything you say can and will be used against you. So when they ask you of a situation of what you didn't like about your colleagues, you invoke Amendment 5: "I never had a situation where I didn't like my colleagues". When they ask you about how you handled a missed deadline you answer: "I never missed a deadline". And so on. They won't hire you probably any way. No point giving them pigs material to use against you.

time0ut• 1 year ago

This is not the worst interview question I have seen, but it sure could use some improvement.

The naming of things is pretty confusing. Async queue, send once, and send many all threw me off and aren't good descriptions for what we are trying to do. I hope this isn't reflective of the company's actual code base. A bit of a red flag.

It also is framed as not a JS question but then the interviewer wants an answer that only makes sense in JS. It also isn't even modern JS. A couple more red flags there.

I dislike questions like this in general, but I've done interviews where they facilitated a decent conversation. It really depends.

It is also just a blog post so hard to infer a lot about the author's actual interview style. Maybe it is great and collaborative. It does remind me of some of the worst engineers I have ever worked with and their interview style though...

jwrallie• 1 year ago

I think also trying to work around a faulty server with client code is a bit weird, I could see it happening in practice but my first instinct given this interview would be to insist the server should receive some attention first, or if it is impossible at least this queue should be implemented by another process or machine near the server side.

I agree this could work if framed as a coworker rubber ducking his problems to you and asking for ideas to get to a solution, because it could clear up the naming issues and focus on the candidate solving problem skills without the pressure about giving the one right answer to the problem.

tekkk2• 1 year ago

Heh heh. I dont understand what the fuss is about, AsyncQueue is kinda cool in JS. I use it, from time to time, to implement async generators that can be iterated over with for await.

Although my implementation doesnt have any sequencing as never had need for it but, more importantly, it has retrying and timeouts. Well retrying I might have implemented on level higher.

Maybe I'm just one of the rare few who actually would have enjoyed this type of question as a chance to brag about my version. Kinda neat as I've never been interested in programming challenges to, for once, know exactly the solution.

tekkk2• 1 year ago

While I'm at it, here's my version, if people want to see and give feedback:

  export interface AsyncQueueOptions {
    timeoutSeconds?: number
  }

  export class AsyncQueue<T> {
    private readonly queue: Promise<T | undefined>[] = []
    readonly timeoutSeconds: number
    private timeout: ReturnType<typeof setTimeout> | undefined
    private reject = () => {}
    private resolve = (value: T | PromiseLike<T>) => {}

    /**
     * @param timeoutSeconds @default 25
     */
    constructor({ timeoutSeconds = 25 }: AsyncQueueOptions = {}) {
      this.timeoutSeconds = timeoutSeconds
      if (timeoutSeconds > 100) {
        console.warn(`You are initializing AsyncQueue with over 100s timeout: ${timeoutSeconds}`)
      }
      this.queue.push(
        new Promise<T | undefined>((resolve, reject) => {
          this.resolve = resolve
          this.reject = reject
          this.timeout = setTimeout(() => resolve(undefined), timeoutSeconds * 1000)
        })
      )
    }

    next(): Promise<T | undefined> | undefined {
      return this.queue.shift()
    }

    push(msg: T) {
      this.resolve(msg)
      this.queue.push(
        new Promise<T | undefined>((resolve, reject) => {
          this.resolve = resolve
          this.reject = reject
          clearTimeout(this.timeout)
          this.timeout = setTimeout(() => resolve(undefined), this.timeoutSeconds * 1000)
        })
      )
    }

    close(msg?: T) {
      if (msg) {
        this.resolve(msg)
      }
      clearTimeout(this.timeout)
    }
  }

delegate• 1 year ago

"But that server is faulty!! If it has to handle multiple requests at once, it starts to break down."

Ok. I know this is all hypothetical. But I don't buy this premise.

Why is the server faulty ? In what way does it fail ? How do you know it's because it's processing more than one request at a time ? What if there are multiple clients each doing one request only ? Do you have control over the server code ? If so, fix it there!

---

The point is, this solution is fixing the wrong problem and introducing a new one down the line.

If the bug on the server gets fixed, you've now implemented an artificial performance bottleneck on the client.

Devs who know about it are going to leave the org, others are going to try to 'optimize' the code around it with other hacks, since by allowing these kinds of fixes you're building to the wrong kind of culture. Always fix the root issue.

Or change the premise of the problem.

dekhn4• 1 year ago

In the interview, am I allowed to fix the server (which apparently "breaks down handling concurrent requests") instead of working on this silly programming exercise?

What about proxy solutions? IE, proxies that take concurrent requests and serialize them?

The question mainly seems to be working around framework limitations and broken externalities, and the interviewing is providing a signal ("you do not want to work here")

12_throw_away• 1 year ago

I would respectfully suggest that this entire approach creates a pathological distributed system, where the client is trying to internally keep track of the state of a server, but without any of the supervision tools would need to do so reliably. (And, as a bonus, it's doing this with a callback hell) What happens if either one restarts/crashes? What happens if you accidentally launch 2 clients?

rehevkor52• 1 year ago

Their "proper implementation" lacks sufficient error/exception handling around the callback() call. It'll become permanently broken if it throws anything.

tk90• 1 year ago

Can they read code and debug it in their head?
Strong engineers, however, can break out the two problems and solve them at the same time.

Disagree so much with this. A "good" engineer breaks a problem down, solves them one by one, and avoids mentally juggling multiple things at once if possible.

bravesoul23• 1 year ago

It's a great question if you want a Node.js developer. But what if they come from a Go or Java background.

You shouldn't have a favourite question. You need interview questions that create good information signals efficiently. You want the candidate to show off. If they are not strong on async then give them a threading question or something else.

shallmn• 1 year ago

I have worked in software development for over 35 years. In that time I have found that the most proficient teams are based on having smart people working in teams that get along well. We’d probably call that emotional safety today, but previously, we just said that everyone worked well together. I don’t know what jobs require interviewing for such a specific response, maybe I’ve never needed that skill set on my team. Intelligent, small ego, team players have been the best teams I have worked with, and I’ll continue to hire based on my gut for those individuals.

ozgrakkurt• 1 year ago

This is not really correct, what happens if the server receives a request and starts processing it but couldn’t send ack response?

In this sense what use is the “proper” implementation in the blog?

In general interview programming questions really feel useless, especially if you consider candidates will be optimising for solving interview questions instead of being good at doing their job

Async Queue – One of my favorite programming interview questions

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