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 <javascript:>. > 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. 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