1// run
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 concurrency primitives: classical inefficient concurrent prime sieve.
8
9// Generate primes up to 100 using channels, checking the results.
10// This sieve consists of a linear chain of divisibility filters,
11// equivalent to trial-dividing each n by all primes p ��� n.
12
13package main
14
15// Send the sequence 2, 3, 4, ... to channel 'ch'.
16func Generate(ch chan<- int) {
17	for i := 2; ; i++ {
18		ch <- i // Send 'i' to channel 'ch'.
19	}
20}
21
22// Copy the values from channel 'in' to channel 'out',
23// removing those divisible by 'prime'.
24func Filter(in <-chan int, out chan<- int, prime int) {
25	for i := range in { // Loop over values received from 'in'.
26		if i%prime != 0 {
27			out <- i // Send 'i' to channel 'out'.
28		}
29	}
30}
31
32// The prime sieve: Daisy-chain Filter processes together.
33func Sieve(primes chan<- int) {
34	ch := make(chan int) // Create a new channel.
35	go Generate(ch)      // Start Generate() as a subprocess.
36	for {
37		// Note that ch is different on each iteration.
38		prime := <-ch
39		primes <- prime
40		ch1 := make(chan int)
41		go Filter(ch, ch1, prime)
42		ch = ch1
43	}
44}
45
46func main() {
47	primes := make(chan int)
48	go Sieve(primes)
49	a := []int{2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97}
50	for i := 0; i < len(a); i++ {
51		if x := <-primes; x != a[i] {
52			println(x, " != ", a[i])
53			panic("fail")
54		}
55	}
56}
57