1// build
2
3// Copyright 2009 The Go Authors. All rights reserved.
4// Use of this source code is governed by a BSD-style
5// license that can be found in the LICENSE file.
6
7// Test basic concurrency: the classic prime sieve.
8// Do not run - loops forever.
9
10package main
11
12// Send the sequence 2, 3, 4, ... to channel 'ch'.
13func Generate(ch chan<- int) {
14	for i := 2; ; i++ {
15		ch <- i // Send 'i' to channel 'ch'.
16	}
17}
18
19// Copy the values from channel 'in' to channel 'out',
20// removing those divisible by 'prime'.
21func Filter(in <-chan int, out chan<- int, prime int) {
22	for {
23		i := <-in // Receive value of new variable 'i' from 'in'.
24		if i%prime != 0 {
25			out <- i // Send 'i' to channel 'out'.
26		}
27	}
28}
29
30// The prime sieve: Daisy-chain Filter processes together.
31func Sieve() {
32	ch := make(chan int) // Create a new channel.
33	go Generate(ch)      // Start Generate() as a subprocess.
34	for {
35		prime := <-ch
36		print(prime, "\n")
37		ch1 := make(chan int)
38		go Filter(ch, ch1, prime)
39		ch = ch1
40	}
41}
42
43func main() {
44	Sieve()
45}
46