On Friday, August 30, 2019 at 1:40:33 PM UTC-4, Robert Engels wrote: > > You changed the Read() method incorrectly - it should be using the Read > lock, not the Write lock. > > Still, as I pointed out when I posted it, Play has a problem where it > aborts if all routines are sleeping (not just blocked), so you need to run > it locally. >
My fault. But it doesn't matter, for the Read method is never called (I commented it off). It also crash locally for all goroutines are blocked. > -----Original Message----- > From: T L > Sent: Aug 30, 2019 12:05 PM > To: golang-nuts > Subject: Re: [go-nuts] An old problem: lack of priority select cases > > > > On Friday, August 30, 2019 at 12:39:41 PM UTC-4, Robert Engels wrote: >> >> >> Makes no difference in the code I posted.... as long as they all use the >> same MultiWriterChannel. In fact, others can be late started, as they will >> fail fast if the channel is already closed. >> > > https://play.golang.org/p/pcwIu2w8ZRb > > All go routines are blocked in the modified version. > > >> -----Original Message----- >> From: T L >> Sent: Aug 30, 2019 11:13 AM >> To: golang-nuts >> Subject: Re: [go-nuts] An old problem: lack of priority select cases >> >> >> >> On Friday, August 30, 2019 at 10:35:29 AM UTC-4, Robert Engels wrote: >>> >>> I don't think so. Why do you think that is the case? The RWLock is >>> "fair" in the sense that once the 'closer' attempts to get the lock, it is >>> guaranteed to get it (as the code is structured) - the subsequent readers >>> will queue behind the "writer = closer". >>> >> >> How about unknown/random number of senders and readers? >> >> >>> >>> -----Original Message----- >>> From: T L >>> Sent: Aug 30, 2019 8:50 AM >>> To: golang-nuts >>> Subject: Re: [go-nuts] An old problem: lack of priority select cases >>> >>> @Robert >>> I think there is a difference between the code of @Leo and you. >>> In you code, the Wirte/Read/Close are all possible to block for ever. >>> >>> On Thursday, August 29, 2019 at 8:59:10 PM UTC-4, Robert Engels wrote: >>>> >>>> >>>> Oops. You are right. The original used two different methods Closed() >>>> and Read() and when I refactored I forgot to add the Read lock to the >>>> Read(). That's why you always have code reviews... >>>> >>>> -----Original Message----- >>>> From: T L >>>> Sent: Aug 29, 2019 6:25 PM >>>> To: golang-nuts >>>> Subject: Re: [go-nuts] An old problem: lack of priority select cases >>>> >>>> >>>> >>>> On Wednesday, August 28, 2019 at 10:05:06 PM UTC-4, robert engels wrote: >>>>> >>>>> Here is a version using RWLock https://play.golang.org/p/YOwuYFiqtlf >>>>> >>>> >>>> Doesn't the Read method need to be guarded by the reader lock? >>>> >>>> >>>> >>>>> >>>>> It won’t run correctly in the playground because it terminates when >>>>> all routines are asleep - which happens during the test (not sure why it >>>>> does this, as sleeping is different than a deadlock). >>>>> >>>>> It is probably less efficient, and less orderly than the other example >>>>> using WaitGroup but you get the idea I hope. It forcibly terminates the >>>>> writers before they complete by design. >>>>> >>>>> On Aug 28, 2019, at 4:09 PM, Michel Levieux <m.le...@capitaldata.fr> >>>>> wrote: >>>>> >>>>> One should also be careful regarding the conceptual demands he or she >>>>> is making. >>>>> Having a shared resource (that is complex enough that it cannot be >>>>> atomically accessed or modified) means essentially that "having multiple >>>>> writers being transparent to the readers", fundamentally, is not possible. >>>>> >>>>> From the moment itself when such a resource is shared, there must be >>>>> some sort of mecanism (that one using resources atomically usable) that >>>>> ensures the integrity of it. >>>>> Maybe what you're talking about is having it transparent in terms of >>>>> code, in which case we both agree, but if you're looking for something >>>>> transparent in essence, as in performance, logical construction and all >>>>> the >>>>> rest, I think there is a misunderstanding here: even if it was added in >>>>> the >>>>> language, there would be many many things going on under the hood, as it >>>>> is >>>>> already (and cannot really be otherwise) for channel use alone. >>>>> >>>>> As for the priority using selects, I think it's more of something to >>>>> be dealt with on the "user-side". There are many kinds of priority in >>>>> general, and trying to implement something in the language itself would >>>>> IMO >>>>> either be too specific compared to the nessecary time to do so or it >>>>> would >>>>> probably have a huge overhead on the "classical' use case of the select >>>>> construct. >>>>> + the fact that it is apparently already possible using RWMutexes. >>>>> >>>>> Le mer. 28 août 2019 à 22:37, Marcin Romaszewicz <mar...@gmail.com> a >>>>> écrit : >>>>> >>>>>> Think of a channel as existing for the lifetime of a particular data >>>>>> stream, and not have it be associated with either producer or consumer. >>>>>> Here's an example: >>>>>> >>>>>> https://play.golang.org/p/aEAXXtz2X1g >>>>>> >>>>>> The channel here is closed after all producers have exited, and all >>>>>> consumers continue to run until the channel is drained of data. >>>>>> >>>>>> The producers are managed by something somewhere in your code - and >>>>>> that is the scope at which it makes sense to create channel ownership. >>>>>> I've >>>>>> used a waitgroup to ensure that the channel is closed after all >>>>>> producers >>>>>> exit, but you can use whatever barrier construct you want. >>>>>> >>>>>> Even if you must have a channel per producer, you can safely close >>>>>> the producer side, without notifying the downstream about this. The >>>>>> example >>>>>> early in the thread uses multiple channels, with one channel being used >>>>>> to >>>>>> signal that the producers should exit. Channels aren't really the right >>>>>> model for this, you want a thread safe flag of some sort. For example: >>>>>> >>>>>> var exitFlag uint64 >>>>>> func producer(chan data int, wg *sync.WaitGroup) { >>>>>> defer wg.Done() >>>>>> for { >>>>>> shouldExit := atomic.LoadUint64(&exitFlag) >>>>>> if shouldExit == 1 { >>>>>> return >>>>>> } >>>>>> chan <- rand.Intn(100) >>>>>> } >>>>>> } >>>>>> >>>>>> Here's 10 producers and 3 consumers sharing a channel and closing it >>>>>> safely upon receiving an exit flag: >>>>>> https://play.golang.org/p/RiKi1PGVSvF >>>>>> >>>>>> -- Marcin >>>>>> >>>>>> On Wed, Aug 28, 2019 at 11:29 AM Leo Lara <l...@leopoldolara.com> >>>>>> wrote: >>>>>> >>>>>>> I do not think priority select is *necessary*, it could be a nice >>>>>>> addition if the performance does not change. >>>>>>> >>>>>>> On Wednesday, August 28, 2019 at 8:27:36 PM UTC+2, Leo Lara wrote: >>>>>>>> >>>>>>>> Hi Robert, >>>>>>>> >>>>>>>> From the article: """To bound more the problem, in my case, you >>>>>>>> control the writers but not the readers""" >>>>>>>> >>>>>>>> So what I was trying to do was to be able to close, with mutiple >>>>>>>> writers, while being transparent for the readers. The readers only >>>>>>>> need to >>>>>>>> read as usual form the channel. >>>>>>>> >>>>>>>> For example, if you want to write a library where the user just >>>>>>>> reads from a channel, this is an approach I found where the user of >>>>>>>> the >>>>>>>> lirbary deos nto have to do anything special. Of course, there might >>>>>>>> be >>>>>>>> another solution, but if you need to modify the reader we are talking >>>>>>>> about >>>>>>>> a different problem. >>>>>>>> >>>>>>>> Cheers!! >>>>>>>> >>>>>>>> On Wednesday, August 28, 2019 at 7:17:24 PM UTC+2, Robert Engels >>>>>>>> wrote: >>>>>>>>> >>>>>>>>> A better solution is to wrap the writes using a RWLock, grab the >>>>>>>>> read lock for writing, and the Write lock for closing. Pretty simple. >>>>>>>>> >>>>>>>>> Just encapsulate it all in a MultiWriterChannel struct - generics >>>>>>>>> would help here :) >>>>>>>>> >>>>>>>>> -----Original Message----- >>>>>>>>> From: Leo Lara >>>>>>>>> Sent: Aug 28, 2019 11:24 AM >>>>>>>>> To: golang-nuts >>>>>>>>> Subject: [go-nuts] Re: An old problem: lack of priority select >>>>>>>>> cases >>>>>>>>> >>>>>>>>> This is connected with my article: >>>>>>>>> https://dev.to/leolara/closing-a-go-channel-written-by-several-goroutines-52j2 >>>>>>>>> >>>>>>>>> I think there I show it is possible to workaround that limitation >>>>>>>>> using standard Go tools. Of course, the code would be simple with >>>>>>>>> priority >>>>>>>>> select, but also perhaps select would become less efficient. >>>>>>>>> >>>>>>>>> On Wednesday, August 28, 2019 at 6:06:33 PM UTC+2, T L wrote: >>>>>>>>>> >>>>>>>>>> The old thread: >>>>>>>>>> https://groups.google.com/forum/#!topic/golang-nuts/ZrVIhHCrR9o >>>>>>>>>> >>>>>>>>>> Go channels are flexible, but in practice, I often encountered >>>>>>>>>> some situations in which channel are hard to use. >>>>>>>>>> Given an example: >>>>>>>>>> >>>>>>>>>> import "math/rand" >>>>>>>>>> >>>>>>>>>> type Producer struct { >>>>>>>>>> data chan int >>>>>>>>>> closed chan struct{} >>>>>>>>>> } >>>>>>>>>> >>>>>>>>>> func NewProducer() *Producer { >>>>>>>>>> p := &Producer { >>>>>>>>>> data: make(chan int), >>>>>>>>>> closed: make(chan struct{}), >>>>>>>>>> } >>>>>>>>>> >>>>>>>>>> go p.run() >>>>>>>>>> >>>>>>>>>> return p >>>>>>>>>> } >>>>>>>>>> >>>>>>>>>> func (p *Produce) Stream() chan int { >>>>>>>>>> return p.data >>>>>>>>>> } >>>>>>>>>> >>>>>>>>>> func (p *Producer) run() { >>>>>>>>>> for { >>>>>>>>>> // If non-blocking cases are selected by their appearance >>>>>>>>>> order, >>>>>>>>>> // then the following slect block is a perfect use. >>>>>>>>>> select { >>>>>>>>>> case(0) <-p.closed: return >>>>>>>>>> case p.data <- rand.Int(): >>>>>>>>>> } >>>>>>>>>> } >>>>>>>>>> } >>>>>>>>>> >>>>>>>>>> func (p *Produce) Clsoe() { >>>>>>>>>> close(p.closed) >>>>>>>>>> close(p.data) >>>>>>>>>> } >>>>>>>>>> >>>>>>>>>> func main() { >>>>>>>>>> p := NewProducer() >>>>>>>>>> for n := p.Stream() { >>>>>>>>>> // use n ... >>>>>>>>>> } >>>>>>>>>> } >>>>>>>>>> >>>>>>>>>> >>>>>>>>>> If the first case in the select block in the above example has a >>>>>>>>>> higher priority than the second one, >>>>>>>>>> then coding will be much happier for the use cases like the above >>>>>>>>>> one. >>>>>>>>>> >>>>>>>>>> In short, the above use case requires: >>>>>>>>>> * for receivers, data streaming end is notified by the close of a >>>>>>>>>> channel. >>>>>>>>>> * for senders, data will never be sent to closed channel. >>>>>>>>>> >>>>>>>>>> But, as Go 1 doesn't support priority select cases, it is much >>>>>>>>>> tedious to implement the code >>>>>>>>>> satisfying the above listed requirements. The final >>>>>>>>>> implementation is often very ugly and inefficient. >>>>>>>>>> >>>>>>>>>> Does anyone else also experience the pain? >>>>>>>>>> >>>>>>>>> >>>>>>>>> -- >>>>>>>>> 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/b284f880-034a-4721-8686-ef48d3e2c14c%40googlegroups.com >>>>>>>>> >>>>>>>>> <https://groups.google.com/d/msgid/golang-nuts/b284f880-034a-4721-8686-ef48d3e2c14c%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/aeb38a0a-8268-42d7-a8eb-ce5ef01c5380%40googlegroups.com >>>>>>> >>>>>>> <https://groups.google.com/d/msgid/golang-nuts/aeb38a0a-8268-42d7-a8eb-ce5ef01c5380%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/CA%2Bv29LvcUhUvrZb_8AKYWj0A%2Bqd5LKBPmbz-RVBb%3DJn_gNZE6w%40mail.gmail.com >>>>>> >>>>>> <https://groups.google.com/d/msgid/golang-nuts/CA%2Bv29LvcUhUvrZb_8AKYWj0A%2Bqd5LKBPmbz-RVBb%3DJn_gNZE6w%40mail.gmail.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/CANgi337s1Low95QvqJUAOTsqcVji7uMQ_jr%3DFftpt2uMz5_XSQ%40mail.gmail.com >>>>> >>>>> <https://groups.google.com/d/msgid/golang-nuts/CANgi337s1Low95QvqJUAOTsqcVji7uMQ_jr%3DFftpt2uMz5_XSQ%40mail.gmail.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/a5cff3f8-cc1c-4719-9f2f-7b9c31086f6a%40googlegroups.com >>>> >>>> <https://groups.google.com/d/msgid/golang-nuts/a5cff3f8-cc1c-4719-9f2f-7b9c31086f6a%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/4bf95bb2-33ed-46ed-9436-48df1072914f%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/golang-nuts/4bf95bb2-33ed-46ed-9436-48df1072914f%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/d155dcf6-7c01-4f7e-b408-eef9903cd837%40googlegroups.com >> >> <https://groups.google.com/d/msgid/golang-nuts/d155dcf6-7c01-4f7e-b408-eef9903cd837%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/74653e49-f374-4ac8-998e-fd874cdf6bd4%40googlegroups.com > > <https://groups.google.com/d/msgid/golang-nuts/74653e49-f374-4ac8-998e-fd874cdf6bd4%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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