Would you please elaborate on that?
As I understand it there is no concurrent use of len happening here. It's a
for loop and all calling to len is happening sequentially. Unless the
channels make the code inside cases of one select statement concurrent -
which will be super confusing for me.
On Sunday, August 28, 2016 at 8:03:10 PM UTC+4:30, Jan Mercl wrote:
>
> Using len(ch) like this in a concurrency scenario is a big no because then
> the value you get carries 0 bits of useful information. It's not a data
> race, it's worse, the race is semantic and not fixable without removing the
> use of len(ch).
>
> On Sun, Aug 28, 2016, 17:26 dc0d <kaveh.sh...@gmail.com <javascript:>>
> wrote:
>
>> TL;DR
>>
>> Does assigning a (buffered) channel, already in a variable, to a second
>> variable, affects the result of len function?
>>
>> Long version:
>> What is happening here? - Code at the end; Go 1.7.
>>
>> *Output 1*:
>>
>> Nine times:
>> [ info ] 2016/08/28 19:51:28 LEN_BEFORE=0
>>
>> [ info ] 2016/08/28 19:51:28 LEN=7
>>
>> [ info ] 2016/08/28 19:51:28 S00=7
>>
>> But if the second case gets commented like this:
>>
>> case <-limiter.C:
>> // if len(actualBuffer) > 0 {
>> // buffer = actualBuffer
>> // } else {
>> // buffer = nil
>> // }
>>
>> It works as expected; *Output2*:
>>
>> [ info ] 2016/08/28 19:54:28 LEN_BEFORE=0
>>
>> [ info ] 2016/08/28 19:54:28 LEN=7
>>
>> [ info ] 2016/08/28 19:54:28 S00=7
>>
>> [ info ] 2016/08/28 19:54:29 LEN_BEFORE=7
>>
>> [ info ] 2016/08/28 19:54:30 LEN_BEFORE=7
>>
>> [ info ] 2016/08/28 19:54:31 LEN_BEFORE=7
>>
>> [ info ] 2016/08/28 19:54:32 LEN_BEFORE=7
>>
>> [ info ] 2016/08/28 19:54:33 LEN_BEFORE=7
>>
>> [ info ] 2016/08/28 19:54:34 LEN_BEFORE=7
>>
>> [ info ] 2016/08/28 19:54:35 LEN_BEFORE=7
>>
>> [ info ] 2016/08/28 19:54:36 LEN_BEFORE=7
>> ...
>>
>> Code:
>>
>> package main
>>
>>
>> import (
>> "log"
>> "time"
>>
>>
>> "github.com/comail/colog"
>> )
>>
>>
>> func status00Channeler() {
>> <-start
>>
>>
>> limiter := time.NewTicker(time.Second / maxMsgPerSec)
>> fetchLimiter := time.NewTicker(time.Second)
>>
>>
>> var buffer chan *Data
>> actualBuffer := make(chan *Data, maxMsgPerSec)
>> db, err := newDB()
>> if err != nil {
>> log.Panic(err)
>> }
>>
>>
>> FIRST:
>> for {
>> select {
>> case <-interrupted:
>> break FIRST
>> case <-limiter.C:
>> // if len(actualBuffer) > 0 {
>> // buffer = actualBuffer
>> // } else {
>> // buffer = nil
>> // }
>> case i := <-buffer:
>> select {
>> case status00 <- i: // will block here
>> case <-interrupted:
>> break FIRST
>> }
>> case <-fetchLimiter.C:
>> log.Printf("LEN_BEFORE=%d", len(actualBuffer))
>> if len(actualBuffer) > 0 {
>> continue
>> }
>>
>>
>> s00, err := db.GetIncomings()
>> if err != nil {
>> log.Println(`error:`, err)
>> time.Sleep(time.Second)
>> continue
>> }
>> if s00 == nil || len(s00) == 0 {
>> continue
>> }
>>
>>
>> FILL_BUFFER:
>> for _, v := range s00 {
>> select {
>> case actualBuffer <- v:
>> default:
>> break FILL_BUFFER
>> }
>> }
>>
>>
>> log.Printf("LEN=%d", len(actualBuffer))
>> log.Printf("S00=%d", len(s00))
>> }
>> }
>> }
>>
>>
>> func main() {
>> go status00Channeler()
>> close(start)
>>
>>
>> <-time.After(time.Second * 30)
>> }
>>
>>
>> var (
>> status00 = make(chan *Data, maxMsgPerSec)
>> )
>>
>>
>> type Data struct{}
>>
>>
>> const (
>> maxMsgPerSec = 60
>> )
>>
>>
>> func newDB() (*DB, error) {
>> res := new(DB)
>> return res, nil
>> }
>>
>>
>> func (db *DB) GetIncomings() ([]*Data, error) {
>> var res []*Data
>> res = append(res, &Data{})
>> res = append(res, &Data{})
>> res = append(res, &Data{})
>> res = append(res, &Data{})
>> res = append(res, &Data{})
>> res = append(res, &Data{})
>> res = append(res, &Data{})
>>
>>
>> return res, nil
>> }
>>
>>
>> type DB struct{}
>>
>>
>> func init() {
>> colog.Register()
>> }
>>
>>
>> var (
>> start = make(chan struct{})
>> interrupted = make(chan struct{}) // comes from sys interrupts SIGINT,
>> SIGTERM, etc
>> )
>>
>>
>> --
>> You received this message because you are subscribed to the Google Groups
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>> To unsubscribe from this group and stop receiving emails from it, send an
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>>
> --
>
> -j
>
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