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 <javascript:>> > 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 <javascript:>. > 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. 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