The code suggests, that select is indeed not fair:
https://github.com/golang/go/blob/a4d03a9bf7604b727abd0a1ebfb118ff6366ee50/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 <tapir....@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+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.
