Your deadlock comes from the channel never being closed so the for loop in your main go routine never ends. You need to add some logic to figure out when to close the channel, or break out of the loop (and then close the channel).
- Will On Fri, Apr 17, 2020 at 2:47 PM Vaibhav <vnzong...@gmail.com> wrote: > Hi, > I didn't want to create a new thread with same topic so though of making a > reply here. > I made a solution for the same problem > https://play.golang.org/p/GP8qVB9FPfx without the use of lock and somehow > it is working, but ends up going in the deadlock! What is going wrong here? > > func Crawl(root string, r_depth int, fetcher Fetcher) { > ch := make(chan struct { > string > int > }) > var wg sync.WaitGroup > crawl := func(url string, depth int) { > defer wg.Done() > if depth <= 0 { > return > } > body, urls, err := fetcher.Fetch(url) > if err != nil { > fmt.Println(err) > return > } > fmt.Printf("found: %s %q\n", url, body) > for _, u := range urls { > ch <- struct { > string > int > }{u, depth - 1} > } > } > urlMap := map[string]bool{root: true} > wg.Add(1) > go crawl(root, r_depth) > for url := range ch { > if _, ok := urlMap[url.string]; !ok { > wg.Add(1) > go crawl(url.string, url.int) > urlMap[url.string] = true > } > } > wg.Wait() > } > > Regards, > Vaibhav > > On Tuesday, August 28, 2012 at 3:07:37 AM UTC+5:30, Kyle Lemons wrote: >> >> Looks pretty good. >> >> On Mon, Aug 27, 2012 at 2:57 AM, Thomas Gawehns <thomas...@gmail.com> >> wrote: >> >>> Hi folks, >>> I'm new to go and must admit i like it. But somehow my solution to the >>> web crawler exercise looks to simple: >>> >>> func Crawl(url string, depth int, fetcher Fetcher) { >>> >>> visitedUrls := make(map[string]bool, 100) >>> >> This is accessed concurrently without a lock. With GOMAXPROCS=1, this >> probably won't blow up, but it's technically a data race and thus not >> "correct." >> >> >>> var InnerCrawl func(url string, depth int, >>> fetcher Fetcher, finish chan bool) >>> InnerCrawl = func (url string, depth int, >>> fetcher Fetcher, finish chan bool) { >>> defer func() { finish<- true } () >>> done := make(chan bool) >>> if depth <= 0 || visitedUrls[url] { >>> return >>> } >>> visitedUrls[url] = true >>> body, urls, err := fetcher.Fetch(url) >>> if err != nil { >>> fmt.Println(err) >>> return >>> } >>> fmt.Printf("found: %s %q\n", url, body) >>> for _, u := range urls { >>> go InnerCrawl(u, depth-1, fetcher, done) >>> } >>> for _ = range urls { >>> <-done >>> } >>> } >>> done := make(chan bool) >>> go InnerCrawl(url, depth, fetcher, done) >>> <-done >>> return >>> } >>> >>> Is there some flaw in it??? >>> rgds Thomas >>> >> >> -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/golang-nuts/a0aebb00-cb03-4bdb-a409-c24f723868d5%40googlegroups.com > <https://groups.google.com/d/msgid/golang-nuts/a0aebb00-cb03-4bdb-a409-c24f723868d5%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAOweqVmdgSzNNQ8ZhEAYd%2BsTLWVsG%3DKuoAzKLtzdvJLEP%2BTPFg%40mail.gmail.com.
