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+// build
+
+// 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 basic concurrency: the classic prime sieve.
+// Do not run - loops forever.
+
+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 := <-in // Receive value of new variable 'i' from 'in'.
+ if i%prime != 0 {
+ out <- i // Send 'i' to channel 'out'.
+ }
+ }
+}
+
+// The prime sieve: Daisy-chain Filter processes together.
+func Sieve() {
+ ch := make(chan int) // Create a new channel.
+ go Generate(ch) // Start Generate() as a subprocess.
+ for {
+ prime := <-ch
+ print(prime, "\n")
+ ch1 := make(chan int)
+ go Filter(ch, ch1, prime)
+ ch = ch1
+ }
+}
+
+func main() {
+ Sieve()
+}