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 13 package main 14 15 // Send the sequence 2, 3, 4, ... to channel 'ch'. 16 func 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'. 24 func 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. 33 func 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 46 func 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
