|
| 1 | +package main |
| 2 | + |
| 3 | +// From https://tour.golang.org/concurrency/10 |
| 4 | + |
| 5 | +import ( |
| 6 | + "fmt" |
| 7 | + "sync" |
| 8 | +) |
| 9 | + |
| 10 | +type Fetcher interface { |
| 11 | + // Fetch returns the body of URL and |
| 12 | + // a slice of URLs found on that page. |
| 13 | + Fetch(url string) (body string, urls []string, err error) |
| 14 | +} |
| 15 | + |
| 16 | +// Crawl uses fetcher to recursively crawl |
| 17 | +// pages starting with url, to a maximum of depth. |
| 18 | +func Crawl(url string, depth int, fetcher Fetcher) { |
| 19 | + // TODO: Fetch URLs in parallel. |
| 20 | + // TODO: Don't fetch the same URL twice. |
| 21 | + // This implementation doesn't do either: |
| 22 | + if depth <= 0 { |
| 23 | + return |
| 24 | + } |
| 25 | + body, urls, err := fetcher.Fetch(url) |
| 26 | + if err != nil { |
| 27 | + fmt.Println(err) |
| 28 | + return |
| 29 | + } |
| 30 | + fmt.Printf("found: %s %q\n", url, body) |
| 31 | + for _, u := range urls { |
| 32 | + Crawl(u, depth-1, fetcher) |
| 33 | + } |
| 34 | + return |
| 35 | +} |
| 36 | + |
| 37 | +// SafeMap includes a mutex for locking the map before reading or writing |
| 38 | +type SafeMap struct { |
| 39 | + mu sync.Mutex |
| 40 | + fetched map[string]bool |
| 41 | +} |
| 42 | + |
| 43 | +// ConcurrentMutexCrawler does parallel crawl and uses a mutex for locking |
| 44 | +func ConcurrentMutexCrawler(url string, mp *SafeMap, fetcher Fetcher) { |
| 45 | + // Check whether url is already fetched or someone is doing it |
| 46 | + mp.mu.Lock() |
| 47 | + urlDone := mp.fetched[url] |
| 48 | + mp.fetched[url] = true // Mark that I'm doing it |
| 49 | + mp.mu.Unlock() |
| 50 | + |
| 51 | + if urlDone { |
| 52 | + return |
| 53 | + } |
| 54 | + |
| 55 | + body, urls, err := fetcher.Fetch(url) |
| 56 | + if err != nil { |
| 57 | + fmt.Println(err) |
| 58 | + return |
| 59 | + } |
| 60 | + |
| 61 | + fmt.Printf("Found: %s %q\n", url, body) |
| 62 | + |
| 63 | + var done sync.WaitGroup |
| 64 | + for _, u := range urls { |
| 65 | + // fmt.Printf("Urls: %s\n", u) |
| 66 | + done.Add(1) |
| 67 | + // Pass as arg otherwise it'll use a different value of u |
| 68 | + // Arg will be a private copy of the goroutine |
| 69 | + go func(url string) { |
| 70 | + ConcurrentMutexCrawler(url, mp, fetcher) |
| 71 | + done.Done() |
| 72 | + }(u) |
| 73 | + } |
| 74 | + |
| 75 | + done.Wait() |
| 76 | +} |
| 77 | + |
| 78 | +func main() { |
| 79 | + // Crawl("https://golang.org/", 4, fetcher) |
| 80 | + |
| 81 | + mp := SafeMap{fetched: make(map[string]bool)} |
| 82 | + ConcurrentMutexCrawler("https://golang.org/", &mp, fetcher) |
| 83 | +} |
| 84 | + |
| 85 | +// fakeFetcher is Fetcher that returns canned results. |
| 86 | +type fakeFetcher map[string]*fakeResult |
| 87 | + |
| 88 | +type fakeResult struct { |
| 89 | + body string |
| 90 | + urls []string |
| 91 | +} |
| 92 | + |
| 93 | +func (f fakeFetcher) Fetch(url string) (string, []string, error) { |
| 94 | + if res, ok := f[url]; ok { |
| 95 | + return res.body, res.urls, nil |
| 96 | + } |
| 97 | + return "", nil, fmt.Errorf("not found: %s", url) |
| 98 | +} |
| 99 | + |
| 100 | +// fetcher is a populated fakeFetcher. |
| 101 | +var fetcher = fakeFetcher{ |
| 102 | + "https://golang.org/": &fakeResult{ |
| 103 | + "The Go Programming Language", |
| 104 | + []string{ |
| 105 | + "https://golang.org/pkg/", |
| 106 | + "https://golang.org/cmd/", |
| 107 | + }, |
| 108 | + }, |
| 109 | + "https://golang.org/pkg/": &fakeResult{ |
| 110 | + "Packages", |
| 111 | + []string{ |
| 112 | + "https://golang.org/", |
| 113 | + "https://golang.org/cmd/", |
| 114 | + "https://golang.org/pkg/fmt/", |
| 115 | + "https://golang.org/pkg/os/", |
| 116 | + }, |
| 117 | + }, |
| 118 | + "https://golang.org/pkg/fmt/": &fakeResult{ |
| 119 | + "Package fmt", |
| 120 | + []string{ |
| 121 | + "https://golang.org/", |
| 122 | + "https://golang.org/pkg/", |
| 123 | + }, |
| 124 | + }, |
| 125 | + "https://golang.org/pkg/os/": &fakeResult{ |
| 126 | + "Package os", |
| 127 | + []string{ |
| 128 | + "https://golang.org/", |
| 129 | + "https://golang.org/pkg/", |
| 130 | + }, |
| 131 | + }, |
| 132 | +} |
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