关于gorouitne

按照a tour of Go 中 Crawl 例程提示，改写了 Crawl 函数，但是只能找出一条 url，想不出原因，请教大家，谢谢。 ``` package main import ( "fmt" "sync" ) type Fetcher interface { // Fetch returns the body of URL and // a slice of URLs found on that page. Fetch(url string) (body string, urls []string, err error) } // Crawl uses fetcher to recursively crawl // pages starting with url, to a maximum of depth. func Crawl(url string, depth int, fetcher Fetcher) { // TODO: Fetch URLs in parallel. // TODO: Don't fetch the same URL twice. // This implementation doesn't do either: if depth <= 0 { fmt.Printf("depth <= 0 return") return } body, urls, err := fetcher.Fetch(url) if err != nil { fmt.Println(err) return } fmt.Printf("found: %s %q\n", url, body) crawled.mux.Lock() crawled.c[url]++ crawled.mux.Unlock() for _, u := range urls { //crawled.mux.Lock() if cnt, ok := crawled.c[u]; ok { cnt++ } else { fmt.Println("go ...", u) go Crawl(u, depth-1, fetcher) } //crawled.mux.Unlock() //Crawl(u, depth-1, fetcher) } return } func main() { Crawl("http://golang.org/", 4, fetcher) } // fakeFetcher is Fetcher that returns canned results. type fakeFetcher map[string]*fakeResult type fakeResult struct { body string urls []string } func (f fakeFetcher) Fetch(url string) (string, []string, error) { if res, ok := f[url]; ok { return res.body, res.urls, nil } return "", nil, fmt.Errorf("not found: %s", url) } // fetcher is a populated fakeFetcher. var fetcher = fakeFetcher{ "http://golang.org/": &fakeResult{ "The Go Programming Language", []string{ "http://golang.org/pkg/", "http://golang.org/cmd/", }, }, "http://golang.org/pkg/": &fakeResult{ "Packages", []string{ "http://golang.org/", "http://golang.org/cmd/", "http://golang.org/pkg/fmt/", "http://golang.org/pkg/os/", }, }, "http://golang.org/pkg/fmt/": &fakeResult{ "Package fmt", []string{ "http://golang.org/", "http://golang.org/pkg/", }, }, "http://golang.org/pkg/os/": &fakeResult{ "Package os", []string{ "http://golang.org/", "http://golang.org/pkg/", }, }, } type crawledUrl struct { c map[string]int mux sync.Mutex } var crawled = crawledUrl{c: make(map[string]int)} ```