I agree. It seems to me that the problem in example 2 is deep in the architecture of the program, not just a detail of the `select` statements. The `connect` function essentially functions as a single-worker “worker pool”, storing the data in a goroutine (specifically, in the closure of the `srv` function). The need for the channels at all seems unmotivated, and so the use of the channels seems inappropriate — I suspect that that is why you aren't finding a satisfactory solution.
Stepping up a level: Egon, you say that you “want to show what not to do.” That is pretty much the premise of my GopherCon 2018 talk, Rethinking Classical Concurrency Patterns (https://www.youtube.com/watch?v=5zXAHh5tJqQ ). I would suggest going back to a more concrete problem and re-examining it with the advice of that talk in mind. (If you would like more detail on how to apply that advice, I'd be happy to take a look at concrete examples — but I agree with Robert that the code posted earlier is too abstract to elicit useful feedback.) On Sunday, December 8, 2019 at 1:57:09 AM UTC-5, Robert Engels wrote: > > I’m sorry, but it’s very hard to understand when you start with solutions. > I think maybe clearly restating the problem will allow more people to offer > up ideas. To be honest at this point I’m not really certain what you’re > trying to demonstrate or why. > > On Dec 8, 2019, at 12:44 AM, Egon Kocjan <eko...@gmail.com <javascript:>> > wrote: > > I meant lock-free as in "without explicit locks". > > The original challenge still stands if someone has a better solution than > me: > "The deadlocks in 2_1.go and 2_2.go are caused by the simplistic and wrong > implementation of bidi-comm, which is what I'll be illustrating. I have > three working solutions - 1_1.go, 2_3.go, 2_4.go. So the question is, can > we remove the extra goroutine from 1_1.go and make the code nicer to read > than 2_3.go and 2_4.go. The extra goroutine that I'd like to be removed is > started here: > https://github.com/egonk/chandemo/blob/master/1_1.go#L14 (line 14)" > > On Sunday, December 8, 2019 at 7:18:16 AM UTC+1, Robert Engels wrote: >> >> I understand what you are saying but I’ll still suggest that your >> premise/design is not correct. There are plenty of useful lock free >> structures in Go (see github.com/robaho/go-concurrency-test) but that is >> not what you are attempting here... you are using async processing - these >> are completely different things. Using async in Go is an anti-pattern IMO. >> >> On Dec 8, 2019, at 12:11 AM, Egon Kocjan <eko...@gmail.com> wrote: >> >> >> I'll cite myself: >> "I'm preparing a short talk about Go channels and select. More >> specifically, I want to show what not to do." >> and >> "it would be tempting to just combine two goroutines into one and handle >> caching in a single loop without using locks (I see developers avoid >> atomics and locks if they don't have a lot of previous experience with >> traditional MT primitives)" >> >> Before I say one can't do something in Go, I wanted to ask here to make >> sure I'm not missing something obvious. Basically, I intend to show how >> difficult lock-free programming can be so don't force it - just use >> goroutines and locks. >> >> On Saturday, December 7, 2019 at 3:46:43 PM UTC+1, Robert Engels wrote: >>> >>> Probably not. Go is designed for 1:1 and there is no reason to do it >>> differently. You could probably try to write an async event driven layer >>> (which it looks like you’ve tried) but why??? >>> >>> It’s like saying I’d really like my plane to float - you can do that >>> -but most likely you want a boat instead of a plane. >>> >>> On Dec 7, 2019, at 2:38 AM, Egon Kocjan <eko...@gmail.com> wrote: >>> >>> >>> I'll try to clarify as best as I can, thanks again to anyone looking at >>> this. >>> >>> The simple server implementation of "output <- input+1" is here and it >>> is not "under our control" - it's what we have to work with: >>> https://github.com/egonk/chandemo/blob/master/server.go >>> >>> The test runner or client is here: >>> https://github.com/egonk/chandemo/blob/master/demo.go (it just pushes >>> in ints and gets server replies back through a connection layer) >>> >>> The deadlocks in 2_1.go and 2_2.go are caused by the simplistic and >>> wrong implementation of bidi-comm, which is what I'll be illustrating. I >>> have three working solutions - 1_1.go, 2_3.go, 2_4.go. So the question is, >>> can we remove the extra goroutine from 1_1.go and make the code nicer to >>> read than 2_3.go and 2_4.go. The extra goroutine that I'd like to be >>> removed is started here: >>> https://github.com/egonk/chandemo/blob/master/1_1.go#L14 (line 14) >>> >>> What I mean by removed - no go statement, replaced presumably by some >>> kind of for/select combination. >>> >>> On Saturday, December 7, 2019 at 7:02:50 AM UTC+1, robert engels wrote: >>>> >>>> I’m sorry but your design is not comprehendible by me, and I’ve done >>>> lots of TCP based services. >>>> >>>> i think you only need to emulate classic TCP processing - a reader >>>> thread (Go routine) on each side of the connection using range to read >>>> until closed. The connection is represented by 2 channels - one for each >>>> direction. >>>> >>>> I think you might be encountering a deadlock because the producer on >>>> one end is not also reading the incoming - so either restructure, or use 2 >>>> more threads for the producers. >>>> >>>> >>>> >>>> On Dec 6, 2019, at 10:38 PM, Egon Kocjan <eko...@gmail.com> wrote: >>>> >>>> Agreed, I see goroutines in general as a big win. But what I intend to >>>> talk about in the presentation: >>>> - we have two unidirectional flows of data resembling something like a >>>> TCP socket, easy to do with two goroutines with a for loop >>>> - let's add caching, so some requests do not go to the server >>>> - it would be tempting to just combine two goroutines into one and >>>> handle caching in a single loop without using locks (I see developers >>>> avoid >>>> atomics and locks if they don't have a lot of previous experience with >>>> traditional MT primitives) >>>> - this is surprisingly difficult to do properly with Go channels, see >>>> my attempts: https://github.com/egonk/chandemo/blob/master/2_3.go and >>>> https://github.com/egonk/chandemo/blob/master/2_4.go >>>> <https://github.com/egonk/chandemo/blob/master/2_3.go> >>>> - it is easy to do in actor systems, just move the code for both actors >>>> into a single actor! >>>> >>>> The lesson here is that select is not a nice and safe compose statement >>>> even if it appears so at the first glance, do not be afraid to use locks. >>>> >>>> Of course, if somebody comes up with a better implementation than >>>> 2_3.go and 2_4.go, I would be very happy to include it in the talk. >>>> >>>> On Saturday, December 7, 2019 at 4:17:04 AM UTC+1, robert engels wrote: >>>>> >>>>> To clarify, with Go’s very lightweight threads it is “doing the >>>>> multiplexing for you” - often only a single CPU is consumed if the >>>>> producer >>>>> and consumer work cannot be parallelized, otherwise you get this >>>>> concurrency “for free”. >>>>> >>>>> You are trying to manually perform the multiplexing - you need async >>>>> structures to do this well - Go doesn’t really support async by design - >>>>> and it’s a much simpler programming model as a result. >>>>> >>>>> On Dec 6, 2019, at 12:02 PM, Robert Engels <ren...@ix.netcom.com> >>>>> wrote: >>>>> >>>>> A channel is much closer to a pipe. There are producers and consumers >>>>> and these are typically different threads of execution unless you have an >>>>> event based (async) system - that is not Go. >>>>> >>>>> On Dec 6, 2019, at 9:30 AM, Egon Kocjan <eko...@gmail.com> wrote: >>>>> >>>>> >>>>> There are goroutines in the examples of course, just a single >>>>> goroutine per bidi channel seems hard. By contrast, I've worked with >>>>> actor >>>>> systems before and they are perfectly fine with a single fiber. >>>>> >>>>> On Friday, December 6, 2019 at 3:38:20 PM UTC+1, Robert Engels wrote: >>>>>> >>>>>> Channels are designed to be used with multiple go routines - if >>>>>> you’re not you are doing something wrong. >>>>>> >>>>>> On Dec 6, 2019, at 8:32 AM, Egon Kocjan <eko...@gmail.com> wrote: >>>>>> >>>>>> >>>>>> Hello >>>>>> >>>>>> I'm preparing a short talk about Go channels and select. More >>>>>> specifically, I want to show what not to do. I chose a bidirectional >>>>>> communication channel implementation, because it seems to be a common >>>>>> base >>>>>> for a lot of problems but hard to implement correctly without using any >>>>>> extra goroutines. All the code is here: >>>>>> https://github.com/egonk/chandemo >>>>>> >>>>>> 1_1.go: easy with en extra goroutine (takes 1.2s for million ints) >>>>>> 2_1.go: nice but completely wrong >>>>>> 2_2.go: better but still deadlocks >>>>>> 2_3.go: correct but ugly and slow (takes more than 2s for million >>>>>> ints) >>>>>> 2_4.go: correct and a bit faster but still ugly (1.8s for million >>>>>> ints) >>>>>> >>>>>> So my question: is there a better way of doing it with just nested >>>>>> for and select and no goroutines? Basically, what would 2_5.go look like? >>>>>> >>>>>> Thank you >>>>>> Egon >>>>>> >>>>>> -- >>>>>> You received this message because you are subscribed to the Google >>>>>> Groups "golang-nuts" group. >>>>>> To unsubscribe from this group and stop receiving emails from it, >>>>>> send an email to golan...@googlegroups.com. >>>>>> To view this discussion on the web visit >>>>>> https://groups.google.com/d/msgid/golang-nuts/82830a5d-2bd8-4324-890e-9ae7f5f0fbaf%40googlegroups.com >>>>>> >>>>>> <https://groups.google.com/d/msgid/golang-nuts/82830a5d-2bd8-4324-890e-9ae7f5f0fbaf%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>>> . >>>>>> >>>>>> >>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "golang-nuts" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to golan...@googlegroups.com. >>>>> To view this discussion on the web visit >>>>> https://groups.google.com/d/msgid/golang-nuts/bdc57eb0-b26f-4364-87fb-241b0807e8ae%40googlegroups.com >>>>> >>>>> <https://groups.google.com/d/msgid/golang-nuts/bdc57eb0-b26f-4364-87fb-241b0807e8ae%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>> . >>>>> >>>>> >>>>> >>>> -- >>>> You received this message because you are subscribed to the Google >>>> Groups "golang-nuts" group. >>>> To unsubscribe from this group and stop receiving emails from it, send >>>> an email to golan...@googlegroups.com. >>>> To view this discussion on the web visit >>>> https://groups.google.com/d/msgid/golang-nuts/75d69b4e-4fb7-4f62-8011-f21e2a4c294a%40googlegroups.com >>>> >>>> <https://groups.google.com/d/msgid/golang-nuts/75d69b4e-4fb7-4f62-8011-f21e2a4c294a%40googlegroups.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>>> >>>> -- >>> You received this message because you are subscribed to the Google >>> Groups "golang-nuts" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to golan...@googlegroups.com. >>> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/golang-nuts/8b87adcc-2249-402c-b34c-20df5013860a%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/golang-nuts/8b87adcc-2249-402c-b34c-20df5013860a%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >>> -- >> You received this message because you are subscribed to the Google Groups >> "golang-nuts" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to golan...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/golang-nuts/3b9bb722-d43f-4e70-8384-dc17cdec6090%40googlegroups.com >> >> <https://groups.google.com/d/msgid/golang-nuts/3b9bb722-d43f-4e70-8384-dc17cdec6090%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> >> -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golan...@googlegroups.com <javascript:>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/4a176af0-74bb-49b5-ae4d-d8714c7bc46d%40googlegroups.com > > <https://groups.google.com/d/msgid/golang-nuts/4a176af0-74bb-49b5-ae4d-d8714c7bc46d%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. 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