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// run
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Test concurrency primitives: classical inefficient concurrent prime sieve.
// Generate primes up to 100 using channels, checking the results.
// This sieve consists of a linear chain of divisibility filters,
// equivalent to trial-dividing each n by all primes p ≤ n.
package main
// Send the sequence 2, 3, 4, ... to channel 'ch'.
func Generate(ch chan<- int) {
for i := 2; ; i++ {
ch <- i // Send 'i' to channel 'ch'.
}
}
// Copy the values from channel 'in' to channel 'out',
// removing those divisible by 'prime'.
func Filter(in <-chan int, out chan<- int, prime int) {
for i := range in { // Loop over values received from 'in'.
if i%prime != 0 {
out <- i // Send 'i' to channel 'out'.
}
}
}
// The prime sieve: Daisy-chain Filter processes together.
func Sieve(primes chan<- int) {
ch := make(chan int) // Create a new channel.
go Generate(ch) // Start Generate() as a subprocess.
for {
// Note that ch is different on each iteration.
prime := <-ch
primes <- prime
ch1 := make(chan int)
go Filter(ch, ch1, prime)
ch = ch1
}
}
func main() {
primes := make(chan int)
go Sieve(primes)
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}
for i := 0; i < len(a); i++ {
if x := <-primes; x != a[i] {
println(x, " != ", a[i])
panic("fail")
}
}
}
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