...

Source file test/chan/sieve1.go

Documentation: test/chan

```     1  // run
2
4  // Use of this source code is governed by a BSD-style
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
```

View as plain text