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Source file test/chan/sieve1.go

Documentation: test/chan

  // 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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