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