Yes. The random number generator employed (right above from what I linked to; the fastrand function), apparently, is unsurprisingly imperfect.
On Fri, Oct 27, 2017 at 10:47 PM, T L <tapir....@gmail.com> wrote: > It is also not uniform for powers of two. > If there a 8 cases, the sixth one will only get a 80% chance of the first > one. > > On Friday, October 27, 2017 at 4:33:47 PM UTC-4, Axel Wagner wrote: >> >> The code suggests, that select is indeed not fair: >> https://github.com/golang/go/blob/a4d03a9bf7604b727abd0a1ebf >> b118ff6366ee50/src/runtime/stubs.go#L109 >> Which seems fine to me. A fair, uniform PRNG for ranges that are not >> powers of two gets a fair bit of overhead and no program should depend on >> uniformity of select for correctness anyway. >> >> On Fri, Oct 27, 2017 at 10:28 PM, T L <tapi...@gmail.com> wrote: >> >>> It looks the distribution of the RNG results depends on the number of >>> cases. >>> The third case only gets the lowest possibility of there are 6 cases, >>> >>> >>> On Friday, October 27, 2017 at 4:21:12 PM UTC-4, T L wrote: >>>> >>>> A better example to show the inhomogeneity of the selected >>>> possibilities of each case. >>>> >>>> package main >>>> >>>> import "fmt" >>>> >>>> func main() { >>>> foo := make(chan struct{}) >>>> close(foo) >>>> var a, b, c, d, e, f, g float64 >>>> fa := func(){a++} >>>> fb := func(){b++} >>>> fc := func(){c++} >>>> fd := func(){d++} >>>> fe := func(){e++} >>>> ff := func(){f++} >>>> fg := func(){g++} >>>> for i := 0; i < 1000000; i++ { >>>> select { >>>> case <-foo: fa() >>>> case <-foo: fb() >>>> case <-foo: fc() >>>> case <-foo: fd() >>>> case <-foo: fe() >>>> case <-foo: ff() >>>> case <-foo: fg() >>>> } >>>> } >>>> fmt.Println(a/a) >>>> fmt.Println(b/a) >>>> fmt.Println(c/a) >>>> fmt.Println(d/a) >>>> fmt.Println(e/a) >>>> fmt.Println(f/a) >>>> fmt.Println(g/a) >>>> } >>>> >>>> result: >>>> >>>> 1 >>>> 0.9999052991869258 >>>> 0.9015652691532394 >>>> 0.9691884140319548 >>>> 0.966320332264567 >>>> 0.9669020658305938 >>>> 0.9604624105415533 >>>> >>>> On Friday, October 27, 2017 at 4:08:39 PM UTC-4, T L wrote: >>>>> >>>>> The following program constantly prints a value larger than 1.02 >>>>> >>>>> package main >>>>> >>>>> import "fmt" >>>>> >>>>> func main() { >>>>> foo, bar := make(chan struct{}), make(chan struct{}) >>>>> close(foo) >>>>> close(bar) >>>>> x, y := 0.0, 0.0 >>>>> f := func(){x++} >>>>> g := func(){y++} >>>>> for i := 0; i < 1000000; i++ { >>>>> select { >>>>> case <-bar: g() >>>>> case <-foo: f() >>>>> case <-bar: g() >>>>> case <-foo: f() >>>>> case <-bar: g() >>>>> case <-foo: f() >>>>> } >>>>> } >>>>> fmt.Println(x/y) >>>>> } >>>>> >>>>> if the last two cases are removed, then it becomes quit fair. >>>>> >>>> -- >>> 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 golang-nuts...@googlegroups.com. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> -- > 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 golang-nuts+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. > -- 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 golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
