8 ms·

What Color is Your Function? (2015)

109 points by thinkloop 9y ago

hyperion2010 9y ago
Just the other day I was looking over my notes from (horror of horrors) 3 years ago on core problems to avoid when designing a language, and this article came up. Still just as good a read as I remembered, made all the more pertinent by the intervening time in which I have repeatedly cursed python's implementation for the massive friction burns it has caused me. Probably needs a (2015) on it for context, but I consider it timeless!
- deleted 9y ago
  [deleted]
throwaway13337 9y ago
Async web servers are more complex than thread per connection ones. I think that's the big thing the author is communicating. It's true. And most types of development don't need async io. It's worth talking about. The author makes the mistake of calling this a language problem and not a web server problem. With python, Java, c#, and hell, even js, you can have a thread per connection web server if you choose to. This will avoid many async woes. It's just not trendy.
- hliyan 9y ago
  This seems like a good faith comment. I'm not really sure why it's getting downvoted. Someone care to shed some light?
  - TomMarius 9y ago
    Nowadays people downvote because they disagree. It's sad because it pointlessly frustrates the poster and kills discussions.
    - steveklabnik 9y ago
      It's not just 'nowadays'. pg a decade ago: https://news.ycombinator.com/item?id=117171 https://news.ycombinator.com/item?id=117171 > I think it's ok to use the up and down arrows to express agreement.
      - TomMarius 9y ago
        From my personal point of view, it's happening more in the last year than it did before.
- eecc 9y ago
  Except I remember my times as sysadmin, putting out fires on Tomcats brought to their knees by 1 poorly performing query and a few impatient users hitting F5. Yes, async is indeed more complex but it is a measurable improvement over previous - thread based - designs, and it is trivial to hit scenarios where it will make a difference. Just like anything though, it must be applied sensibly: not every single call must be decomposed into a choreography of async collaborators (yes, listen that, it’s “architecture talk”, it’s like that dark language used in Mordor that even Gandalf is scared to pronounce. Ever worked on a DDD/CQRS/ES project? ;)
- xtrapolate 9y ago
  > "It's just not trendy." The "thread-per-connection" model doesn't scale. It's simply not resource-efficient in any way.
  - vosper 9y ago
    I suspect it scales plenty for what most people are actually trying to do. Especially if the cost of throwing a few more web servers at the problem is less than the extra developer time that it costs to live in the async world. You can have quite a lot of threads on a fairly cheap machine these days.
    - adventured 9y ago
      99%+ of all use cases will never need the kind of scaling that async is more ideal for. A small fraction of 1% of all sites/services will ever push more than 10k or 20k uniques per day. With today's infrastructure you can trivially run a large number of the Quantcast US top 5,000 sites on boring old PHP 7.x (which is very fast) with MySQL or Postgres and a cost effective VPS cluster from Digital Ocean. All of these use cases that talk about even a thousand simultaneous connections, are elite 1/10th of 1/10th of 1% of all use case scenarios. Async is comical overkill for nearly everyone, unless you've got a very resource hungry service or a vast number of users. Exceptionally few developers ever run into that scenario. Optimizing that 5% or 10% resource savings when you're pushing 15% of the resources of a single machine, is a waste of time that should be focused on product instead. The first site I ever got into that bracket of traffic, into the Quancast top 3k, it cost me $550 per month for two machines, using Nehalem 5500 processors and 24gb of ram. That was 2011-2012, and 1.x million uniques per month. That was using PHP 5.x and MySQL. And it was overkill by about 50%, while serving up entirely dynamic pages with zero caching and no CDN. US traffic & usage hasn't increased much since 2012, unless you're one of the few hyper scale services. Mostly the audience growth has been stagnant, while the hardware has kept getting better. Today you can run what I was back then for $80 on two VPS machines. Do some use cases need async? Absolutely. Do most? Not even remotely close.
      - kthejoker2 9y ago
- 2sk21 9y ago
  Everytimee I have to wade into Node, I feel like they are reinventing the early days of programming with cooperative multi-tasking.
- pjc50 9y ago
  Ultimately the problem is "the system needs to retain enough state per connection to resume executing the 'next' step of the communication". This state is currently split into different pieces and spread around the system. The operating system maintains the TCP state, for example. If you use threads to partition connections, the operating system looks after the instruction pointer to resume a non-running thread at. The program (whatever language) will usually have some kind of stream state and maybe buffers. It's all a question of where you want to put the abstraction boundaries. Heavy threads? Light threads? Async? Continuations? Or go the other way and have process-per-core with userland drivers and TCP state, where each process is just listening for interrupts and handles everything from there?
  - zbentley 9y ago
    > Or go the other way and have process-per-core with userland drivers and TCP state, where each process is just listening for interrupts and handles everything from there? A kernel. You are describing a kernel, minus workers, plus a web server.
    - pjc50 9y ago
      I was thinking of things like https://shader.kaist.edu/mtcp/ https://shader.kaist.edu/mtcp/ , or https://github.com/snabbco/snabb https://github.com/snabbco/snabb or these kind of things: https://jvns.ca/blog/2016/06/30/why-do-we-use-the-linux-kernels-tcp-stack/ https://jvns.ca/blog/2016/06/30/why-do-we-use-the-linux-kern...
- bennofs 9y ago
  With green threads, I think you can have async io but with threads. When your current thread is making an async call, suspend the green thread (cheap) and yield back to the event loop. Threads are woken up when their async call finishes. This avoids the overhead of real OS threads per connection.
littlestymaar 9y ago
This article has already been posted 3 times on HN, and have been extensively discussed the first time here: https://news.ycombinator.com/item?id=8984648 https://news.ycombinator.com/item?id=8984648
skrebbel 9y ago
I agree with the article but not with the editorialization in the title. In the last 2 years I've mostly used Elixir and JavaScript. In Elixir, generally all functions are synchronous. In JavaScript, there's the typical two-color functions that the author describes: synchronous and asynchronous. Elixir is nicer by far for a lot of parallel programming. Our backend can handle large loads on a single VM simply because of this. However, the world is asynchronous. It's very nice that Elixir abstracts it away, but sometimes that's not what you want and then Elixir makes things significantly harder than JavaScript. For example, imagine that my backend gets many parallel requests for mildly different resources. Each resource needs to query some other system (some 3rd party API, a DB, whatever), but it turns out that many of them will do exactly the same request to that other system even though the user requests they're handling are all pretty much unique. A simple solution is to cache the requests every second/minute/whatever and combine them all. This is nontrivial because I want to cache the running requests, not the responses. If there's one request running, I don't want to launch an identical request. In Elixir, I have to carefully design a GenServer to make this work properly. Or maybe use a library such as the fantastic `memoize`[0] which is great for this, and can even do it without spawning any additional processes at all. But in any way, I have to add complexity - either complexity that I write or complexity that I import. `memoize`'s core caching code is amazing, but not trivial[1]. In JavaScript, I can just cache a bunch of promises in a Map or an object. If the promise exists and hasn't expired, don't do a new request. Else, do the request and cache the promise. Then, in either case, await the promise and use the result. It's 10 lines of boring code. I still like Elixir better for backends and I'm happy that our backend isn't Node. But I'm writing this to underline that explicit support for asynchronicity can be a feature too. [0] https://github.com/melpon/memoize https://github.com/melpon/memoize [1] https://github.com/melpon/memoize/blob/master/lib/memoize/cache.ex#L94 https://github.com/melpon/memoize/blob/master/lib/memoize/ca...
- mercer 9y ago
  I'm very much a beginner at this, so apologies if I'm missing something obvious, but I find this an interesting scenario to think about (so even just to learn how you would do it in Elixir would be nice). Why not track the fetching processes in another managing process (or ETS)? Whenever a new request comes in, you check if it there's a process already busy fetching that particular resource. If there is, ask it to send the results back to this request process too, or use whatever storage that keeps this data to satisfy both requests. In practice I'd probably be using some kind of managing process anyways, to deal with queuing multiple requests to 3rd party provider (because rate limiting and whatnot), and I'd perhaps also have some storage and 'inform requesting party of result' logic/process in place too, so I'd not be adding too much extra complexity. Is this a valid approach to begin with? Or does this expose me as very much an Elixir/OTP beginner :)? And if the approach works, what complexity am I missing compared to keeping track of promises in a map? Or am I overestimating how much complexity you're talking about? I had my first taste of doing some 'real' stuff exactly with caching responses and dealing with rate limiting and whatnot, and I found that to be quite nice to do in Elixir, but this particular 'problem' strikes me as one I'll probably run into fairly soon.
kabes 9y ago
Fibers (coroutines) solves most of the criticism for JS. Although not part of the language and you need to extend v8, it's a viable option for webservers. I believe that's how the Meteor framework has been doing it years before async/await or even promises was a thing.
miracle2k 9y ago
See also this reply: The Function Colour Myth (https://lukasa.co.uk/2016/07/The_Function_Colour_Myth/ https://lukasa.co.uk/2016/07/The_Function_Colour_Myth/).
- Shoothe 9y ago
  I don't see how this reply addresses the core point, it just argues that async await is useful (that's fine but not novel by itself). It is possible to work around the "color" by using generators [0], that way one algorithm can be used in synchronous and asynchronous way. Async await tightly bind to underlying Promises. [0]: https://curiosity-driven.org/promises-and-generators#decoupling https://curiosity-driven.org/promises-and-generators#decoupl...
deleted 9y ago
[deleted]
wokwokwok 9y ago
Please add a 2015 tag, this is old and has previously been extensively discussed.
egnehots 9y ago
And a great sage would say that it all boils down to category theory.
mcv 9y ago
> Wanna know one that doesn’t? Java. Unless you use Vert.x of course. A year ago I helped a friend on a big project in Java for which he was using Vert.x. Suddenly I find myself doing Javascript-style programming in Java. Convenient for calls to other services (a payment provider, for example), but indeed a bit cumbersome if you're used to Java being synchronous.

109 points by thinkloop 9y ago

hyperion2010 9y ago

Just the other day I was looking over my notes from (horror of horrors) 3 years ago on core problems to avoid when designing a language, and this article came up. Still just as good a read as I remembered, made all the more pertinent by the intervening time in which I have repeatedly cursed python's implementation for the massive friction burns it has caused me. Probably needs a (2015) on it for context, but I consider it timeless!

deleted 9y ago
[deleted]

throwaway13337 9y ago

Async web servers are more complex than thread per connection ones. I think that's the big thing the author is communicating. It's true. And most types of development don't need async io. It's worth talking about. The author makes the mistake of calling this a language problem and not a web server problem. With python, Java, c#, and hell, even js, you can have a thread per connection web server if you choose to. This will avoid many async woes. It's just not trendy.

hliyan 9y ago
This seems like a good faith comment. I'm not really sure why it's getting downvoted. Someone care to shed some light?
- TomMarius 9y ago
  Nowadays people downvote because they disagree. It's sad because it pointlessly frustrates the poster and kills discussions.
  - steveklabnik 9y ago
    It's not just 'nowadays'. pg a decade ago: https://news.ycombinator.com/item?id=117171 https://news.ycombinator.com/item?id=117171 > I think it's ok to use the up and down arrows to express agreement.
    - TomMarius 9y ago
      From my personal point of view, it's happening more in the last year than it did before.
eecc 9y ago
Except I remember my times as sysadmin, putting out fires on Tomcats brought to their knees by 1 poorly performing query and a few impatient users hitting F5. Yes, async is indeed more complex but it is a measurable improvement over previous - thread based - designs, and it is trivial to hit scenarios where it will make a difference. Just like anything though, it must be applied sensibly: not every single call must be decomposed into a choreography of async collaborators (yes, listen that, it’s “architecture talk”, it’s like that dark language used in Mordor that even Gandalf is scared to pronounce. Ever worked on a DDD/CQRS/ES project? ;)
xtrapolate 9y ago
> "It's just not trendy." The "thread-per-connection" model doesn't scale. It's simply not resource-efficient in any way.
- vosper 9y ago
  I suspect it scales plenty for what most people are actually trying to do. Especially if the cost of throwing a few more web servers at the problem is less than the extra developer time that it costs to live in the async world. You can have quite a lot of threads on a fairly cheap machine these days.
  - adventured 9y ago
    99%+ of all use cases will never need the kind of scaling that async is more ideal for. A small fraction of 1% of all sites/services will ever push more than 10k or 20k uniques per day. With today's infrastructure you can trivially run a large number of the Quantcast US top 5,000 sites on boring old PHP 7.x (which is very fast) with MySQL or Postgres and a cost effective VPS cluster from Digital Ocean. All of these use cases that talk about even a thousand simultaneous connections, are elite 1/10th of 1/10th of 1% of all use case scenarios. Async is comical overkill for nearly everyone, unless you've got a very resource hungry service or a vast number of users. Exceptionally few developers ever run into that scenario. Optimizing that 5% or 10% resource savings when you're pushing 15% of the resources of a single machine, is a waste of time that should be focused on product instead. The first site I ever got into that bracket of traffic, into the Quancast top 3k, it cost me $550 per month for two machines, using Nehalem 5500 processors and 24gb of ram. That was 2011-2012, and 1.x million uniques per month. That was using PHP 5.x and MySQL. And it was overkill by about 50%, while serving up entirely dynamic pages with zero caching and no CDN. US traffic & usage hasn't increased much since 2012, unless you're one of the few hyper scale services. Mostly the audience growth has been stagnant, while the hardware has kept getting better. Today you can run what I was back then for $80 on two VPS machines. Do some use cases need async? Absolutely. Do most? Not even remotely close.
    - kthejoker2 9y ago
2sk21 9y ago
Everytimee I have to wade into Node, I feel like they are reinventing the early days of programming with cooperative multi-tasking.
pjc50 9y ago
Ultimately the problem is "the system needs to retain enough state per connection to resume executing the 'next' step of the communication". This state is currently split into different pieces and spread around the system. The operating system maintains the TCP state, for example. If you use threads to partition connections, the operating system looks after the instruction pointer to resume a non-running thread at. The program (whatever language) will usually have some kind of stream state and maybe buffers. It's all a question of where you want to put the abstraction boundaries. Heavy threads? Light threads? Async? Continuations? Or go the other way and have process-per-core with userland drivers and TCP state, where each process is just listening for interrupts and handles everything from there?
- zbentley 9y ago
  > Or go the other way and have process-per-core with userland drivers and TCP state, where each process is just listening for interrupts and handles everything from there? A kernel. You are describing a kernel, minus workers, plus a web server.
  - pjc50 9y ago
    I was thinking of things like https://shader.kaist.edu/mtcp/ https://shader.kaist.edu/mtcp/ , or https://github.com/snabbco/snabb https://github.com/snabbco/snabb or these kind of things: https://jvns.ca/blog/2016/06/30/why-do-we-use-the-linux-kernels-tcp-stack/ https://jvns.ca/blog/2016/06/30/why-do-we-use-the-linux-kern...
bennofs 9y ago
With green threads, I think you can have async io but with threads. When your current thread is making an async call, suspend the green thread (cheap) and yield back to the event loop. Threads are woken up when their async call finishes. This avoids the overhead of real OS threads per connection.

littlestymaar 9y ago

This article has already been posted 3 times on HN, and have been extensively discussed the first time here: https://news.ycombinator.com/item?id=8984648 https://news.ycombinator.com/item?id=8984648

skrebbel 9y ago

I agree with the article but not with the editorialization in the title. In the last 2 years I've mostly used Elixir and JavaScript. In Elixir, generally all functions are synchronous. In JavaScript, there's the typical two-color functions that the author describes: synchronous and asynchronous. Elixir is nicer by far for a lot of parallel programming. Our backend can handle large loads on a single VM simply because of this. However, the world is asynchronous. It's very nice that Elixir abstracts it away, but sometimes that's not what you want and then Elixir makes things significantly harder than JavaScript. For example, imagine that my backend gets many parallel requests for mildly different resources. Each resource needs to query some other system (some 3rd party API, a DB, whatever), but it turns out that many of them will do exactly the same request to that other system even though the user requests they're handling are all pretty much unique. A simple solution is to cache the requests every second/minute/whatever and combine them all. This is nontrivial because I want to cache the running requests, not the responses. If there's one request running, I don't want to launch an identical request. In Elixir, I have to carefully design a GenServer to make this work properly. Or maybe use a library such as the fantastic `memoize`[0] which is great for this, and can even do it without spawning any additional processes at all. But in any way, I have to add complexity - either complexity that I write or complexity that I import. `memoize`'s core caching code is amazing, but not trivial[1]. In JavaScript, I can just cache a bunch of promises in a Map or an object. If the promise exists and hasn't expired, don't do a new request. Else, do the request and cache the promise. Then, in either case, await the promise and use the result. It's 10 lines of boring code. I still like Elixir better for backends and I'm happy that our backend isn't Node. But I'm writing this to underline that explicit support for asynchronicity can be a feature too. [0] https://github.com/melpon/memoize https://github.com/melpon/memoize [1] https://github.com/melpon/memoize/blob/master/lib/memoize/cache.ex#L94 https://github.com/melpon/memoize/blob/master/lib/memoize/ca...

mercer 9y ago
I'm very much a beginner at this, so apologies if I'm missing something obvious, but I find this an interesting scenario to think about (so even just to learn how you would do it in Elixir would be nice). Why not track the fetching processes in another managing process (or ETS)? Whenever a new request comes in, you check if it there's a process already busy fetching that particular resource. If there is, ask it to send the results back to this request process too, or use whatever storage that keeps this data to satisfy both requests. In practice I'd probably be using some kind of managing process anyways, to deal with queuing multiple requests to 3rd party provider (because rate limiting and whatnot), and I'd perhaps also have some storage and 'inform requesting party of result' logic/process in place too, so I'd not be adding too much extra complexity. Is this a valid approach to begin with? Or does this expose me as very much an Elixir/OTP beginner :)? And if the approach works, what complexity am I missing compared to keeping track of promises in a map? Or am I overestimating how much complexity you're talking about? I had my first taste of doing some 'real' stuff exactly with caching responses and dealing with rate limiting and whatnot, and I found that to be quite nice to do in Elixir, but this particular 'problem' strikes me as one I'll probably run into fairly soon.

kabes 9y ago

Fibers (coroutines) solves most of the criticism for JS. Although not part of the language and you need to extend v8, it's a viable option for webservers. I believe that's how the Meteor framework has been doing it years before async/await or even promises was a thing.

miracle2k 9y ago

See also this reply: The Function Colour Myth (https://lukasa.co.uk/2016/07/The_Function_Colour_Myth/ https://lukasa.co.uk/2016/07/The_Function_Colour_Myth/).

Shoothe 9y ago
I don't see how this reply addresses the core point, it just argues that async await is useful (that's fine but not novel by itself). It is possible to work around the "color" by using generators [0], that way one algorithm can be used in synchronous and asynchronous way. Async await tightly bind to underlying Promises. [0]: https://curiosity-driven.org/promises-and-generators#decoupling https://curiosity-driven.org/promises-and-generators#decoupl...

deleted 9y ago

[deleted]

wokwokwok 9y ago

Please add a 2015 tag, this is old and has previously been extensively discussed.

egnehots 9y ago

And a great sage would say that it all boils down to category theory.

mcv 9y ago

> Wanna know one that doesn’t? Java. Unless you use Vert.x of course. A year ago I helped a friend on a big project in Java for which he was using Vert.x. Suddenly I find myself doing Javascript-style programming in Java. Convenient for calls to other services (a payment provider, for example), but indeed a bit cumbersome if you're used to Java being synchronous.