This is is an example of prime number sieve
package main
func Generate(ch chan<- int) {
for i := 2; ; i++ {
ch <- i
}
}
func Filter(in <-chan int, out chan<- int, prime int) {
for {
i := <-in
if i%prime != 0 {
out <- i
}
}
}
func main() {
ch := make(chan int)
go Generate(ch)
for i := 0; i < 10; i++ {
prime := <-ch
print(prime, "
")
ch1 := make(chan int)
go Filter(ch, ch1, prime)
ch = ch1
}
}
What I understand is this line of code
prime := <-ch
the channel is waiting for an input and assigns to prime. So, why all the numbers are not printed when the next statement is called
print(prime, "
")
If I remove these last 3 lines
ch1 := make(chan int)
go Filter(ch, ch1, prime)
ch = ch1
then all numbers are printed from 2 to 11. What does this line do ch = ch1?
Thanks
Your code's output is :
2
3
5
7
11
13
17
19
23
29
So the procedure is like this :
i=0,
after prime := <-ch , prime=2, ch = {3};
after go Filter(ch, ch1, prime) , mark as Filter0,in function Filter0 channel in will be 3,4,5,6 ... and channel out will be 3,5,7 ...;
After ch = ch1, So ch = {3}, which will be 3,5,7.
i=1,
after prime := <-ch ,prime= 3, ch ={5},why is there 5 in ch?'Cause now ch is the ch1 in last loop ;
after go Filter(ch, ch1, prime) , mark as Filter1,in function Filter1 channel in will be 5,7,9,11 ... and channel out will be 5,7,11 ...;
After ch = ch1, So ch = {3}, which will be 5,7,11.
i=2, the same .
That how it output.
The reason not all numbers are printed is because it's not the same channel in each iteration of the loop. It creates a new channel ch1 and filters values from ch into ch1 and then it assigns ch to ch1 so that the next iteration ch is the new channel from the previous iteration (there known as ch1) and the values there have been filtered by the Filter goroutine.
Here is another way to write it that may make more sense to you:
for i := 0; i < 10; i++ {
prime := <-ch
print(prime, "
")
oldch := ch //here oldch references the old channel
ch = make(chan int) //and here ch is replaced with a new channel
go Filter(oldch, ch, prime) //and here a filter is applied to values from oldch to ch
}