Roughly, select proceeds in two passes[0]: 1. Figure out what select-cases have events that can fire. 2. Pick fairly among the eligible events. Fairly means pseudo-random.
What likely happens in your case is that your consumer is able to empty out one of the channels which then means the other channel is then selected only. This creates an erratic pattern in which part of your measurement is determined by the internal schedule of goroutines and physical machine characteristics. To verify this, produce 300000 messages into each channel before starting, so it is only the consume loop you are measuring. [0] of course, the whole truth is here: https://golang.org/ref/spec#Select_statements On Thu, Jan 26, 2017 at 1:06 PM T L <tapir....@gmail.com> wrote: > > package main > > import "fmt" > > func main() { > c0, c1 := make(chan int, 10), make(chan int, 10) > > go func() { > for { > c0 <- 0 > } > }() > > go func() { > for { > c1 <- 1 > } > }() > > var n0, n1 int > > f0 := func() { > n0++ > } > > f1 := func() { > n1++ > } > > // pass one > > n0, n1 = 0, 0 > for range [300000]struct{}{} { > select { > case <- c0: f0() > case <- c1: f1() > } > } > > fmt.Printf("pass one: %d/%d=%.2f \n", n0, n1, float64(n0) / > float64(n1)) > > // pass two > > n0, n1 = 0, 0 > for range [300000]struct{}{} { > select { > case <- c0: f0() > case <- c1: f1() > case <- c1: f1() > } > } > > fmt.Printf("pass two: %d/%d=%.2f \n", n0, n1, float64(n0) / > float64(n1)) > > // pass three > > n0, n1 = 0, 0 > for range [300000]struct{}{} { > select { > case <- c0: f0() > case <- c0: f0() > case <- c1: f1() > } > } > > fmt.Printf("pass three: %d/%d=%.2f \n", n0, n1, float64(n0) / > float64(n1)) > } > > The output: > > pass one: 154970/145030=1.07 > pass two: 177853/122147=1.46 > pass three: 127768/172232=0.74 > > -- > 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.
