golang: strange issue with coroutines and channels - go

Question

I wrote a test code, but do not understand why I get this result.
My sub() should update or return counter, based on the channel value
send 1 = counter++
send 0 = return counter
I start 10 go routines con().
They should simply send many 1 to channel (this increase counter)
I wait 1 sec and send 0 to channel. What value should I get?
I think first, I get a "random" value,
but i get 100000 (ok 10x 10000 is faster than 1 sec)
Now I change
for i:=0; i < 10; i++ {
to
for i:=0; i < 10000; i++ {
and now my returned value is 1
Why!?
Now uncomment fmt.Println(counter) in main().
As you see counter works and has this "random" number
package main
import (
"fmt"
"time"
)
var ch chan int = make(chan int)
var counter int
func main() {
go sub()
for i:=0; i < 10; i++ { //change to 10000
go con()
}
time.Sleep(1000 * time.Millisecond)
ch <- 0
fmt.Println(<- ch)
//fmt.Println(counter) //uncomment this
}
func sub() {
for c := range ch {
if c == 0 { ch <- counter }
if c == 1 { counter++ }
}
}
func con() {
for i := 0; i < 10000; i++ {
ch <- 1
}
}

Answer 1

with 2 channels, this work:
package main
import (
"fmt"
"time"
)
var ch chan int = make(chan int)
var ch2 chan int = make(chan int)
var counter int
func main() {
go sub()
for i:=0; i < 10000; i++ { //change to 10000
go con()
}
time.Sleep(1000 * time.Millisecond)
ch2 <- 0
fmt.Println(<- ch2)
//fmt.Println(counter) //uncomment this
}
func sub() {
for ;; {
select {
case <- ch:
counter++
case <- ch2:
ch2 <- counter
}
}
}
func con() {
for i := 0; i < 10000; i++ {
ch <- 1
}
}