如果运行像go run 71_hang.go ok
,则可以正常运行。
但是,如果使用go run 71_hang.go nogood
,它将永远运行。
唯一的区别是额外fmt.Print("")
的default
的select
语句。
我不确定,但是我怀疑某种无限循环和竞争条件吗?这是我的解决方案。
注意:这不是死锁,因为Go没死 throw: all goroutines are asleep - deadlock!
package main
import (
"fmt"
"os"
)
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)
}
func crawl(todo Todo, fetcher Fetcher,
todoList chan Todo, done chan bool) {
body, urls, err := fetcher.Fetch(todo.url)
if err != nil {
fmt.Println(err)
} else {
fmt.Printf("found: %s %q\n", todo.url, body)
for _, u := range urls {
todoList <- Todo{u, todo.depth - 1}
}
}
done <- true
return
}
type Todo struct {
url string
depth int
}
// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher) {
visited := make(map[string]bool)
doneCrawling := make(chan bool, 100)
toDoList := make(chan Todo, 100)
toDoList <- Todo{url, depth}
crawling := 0
for {
select {
case todo := <-toDoList:
if todo.depth > 0 && !visited[todo.url] {
crawling++
visited[todo.url] = true
go crawl(todo, fetcher, toDoList, doneCrawling)
}
case <-doneCrawling:
crawling--
default:
if os.Args[1]=="ok" { // *
fmt.Print("")
}
if crawling == 0 {
goto END
}
}
}
END:
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
}
30秒到达战场
ibeautiful
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