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// URLs implements a breadth-first search webcrawler based on the
// example given in section 8.6 of The Go Programming Language.
package main
import (
"flag"
"fmt"
"log"
"net/url"
"runtime/pprof"
"strings"
"sync"
"time"
)
func main() {
maxConcurrency := flag.Int("c", 0, "Maximum number of concurrent queue pushes")
startRawURL := flag.String("url", "", "Entry-point URL")
maxURLs := flag.Int("max", 0, "Maximum number of URLs to collect (omitted or 0 means no limit)")
flag.Parse()
if *maxConcurrency == 0 {
log.Fatal("Missing -c argument")
}
if *maxConcurrency < 1 {
log.Fatalf("Invalid -c argument: %d", *maxConcurrency)
}
if *startRawURL == "" {
log.Fatal("Missing -url argument")
}
if *maxURLs < 0 {
log.Fatalf("Invalid -max argument: %d", *maxURLs)
}
startURL, err := url.Parse(*startRawURL)
if err != nil {
log.Fatal(err)
}
getLeakProfile(func() {
pool(*startURL, *maxConcurrency, *maxURLs)
})
}
func pool(startURL url.URL, maxConcurrency, maxURLs int) {
var wg sync.WaitGroup
urls := make(chan *url.URL)
outlets := make([]<-chan *[]url.URL, maxConcurrency)
for i := range maxConcurrency {
outlets[i] = worker(&wg, i+1, urls)
}
batches := fanIn(outlets...)
dedup := deduplicate(batches)
urls <- &startURL
for u := range dedup {
fmt.Printf("%s\n", u)
urls <- u
}
fmt.Println("waiting")
wg.Wait()
fmt.Println("done")
}
func deduplicate(batches <-chan *[]url.URL) <-chan *url.URL {
out := make(chan *url.URL)
go func() {
defer close(out)
seen := make(map[url.URL]bool)
for batch := range batches {
for _, u := range *batch {
fmt.Println("(deduplicate) got url")
if !seen[u] {
seen[u] = true
out <- &u
fmt.Println("(deduplicate) finished url")
}
}
}
}()
return out
}
func worker(wg *sync.WaitGroup, id int, urls <-chan *url.URL) <-chan *[]url.URL {
out := make(chan *[]url.URL)
wg.Go(func() {
defer close(out)
for u := range urls {
fmt.Printf("(%d) got url\n", id)
doc, err := fetch(*u)
if err != nil {
log.Print(err)
}
batch := findURLs(*u, doc)
out <- &batch
fmt.Printf("(%d) finished url\n", id)
}
})
return out
}
func fanIn(chans ...<-chan *[]url.URL) <-chan *[]url.URL {
out := make(chan *[]url.URL)
var wg sync.WaitGroup
for i, ch := range chans {
wg.Go(func() {
for batch := range ch {
fmt.Printf("(outlet %d) got batch\n", i)
out <- batch
fmt.Printf("(outlet %d) finished batch\n", i)
}
})
}
go func() {
wg.Wait()
close(out)
}()
return out
}
// getLeakProfile runs a leaky program snippet, extracts the goroutine leak profile,
// and writes it to stdout.
func getLeakProfile(leakySnippet func()) {
prof := pprof.Lookup("goroutineleak")
defer func() {
time.Sleep(2 * time.Second)
var content strings.Builder
prof.WriteTo(&content, 2)
// Ignore non leaked goroutines
leaks := strings.SplitSeq(content.String(), "\n\n")
for leak := range leaks {
if strings.Contains(leak, "(leaked)") {
fmt.Println(leak + "\n")
}
}
}()
leakySnippet()
}
|
