On Saturday, August 31, 2019 at 8:24:31 AM UTC-4, Robert Engels wrote: > > If you comment out the read method then all threads will block. That is > the the behavior of an unbuffered channel - a writer blocks until a reader > is ready. Which is why you always need a valid reader running. Unless the > channel is closed and then the writer will panic. > > The code I provided is valid. >
In fact, if I comment out the write instead read part, the code will also crash on all goroutines are blocked. > > On Aug 31, 2019, at 2:40 AM, T L <tapi...@gmail.com <javascript:>> wrote: > > > > 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 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