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package main
import (
"context"
"fmt"
"log"
"net/url"
"sync"
)
func classic(startURL url.URL, maxConcurrency, maxURLs int) {
worklist := make(chan []url.URL)
var numPendingSends int
numPendingSends++
go func() {
worklist <- []url.URL{startURL}
}()
// Crawl the web concurrently.
seen := make(map[url.URL]bool)
count := 1
ctx, cancel := context.WithCancel(context.Background())
var wg sync.WaitGroup
sema := make(chan struct{}, maxConcurrency)
loop:
for ; numPendingSends > 0; numPendingSends-- {
batch := <-worklist
for _, u := range batch {
if !seen[u] {
fmt.Printf("%d. %s\n", count, &u)
count++
seen[u] = true
if len(seen) == maxURLs {
break loop
}
numPendingSends++
wg.Go(func() {
select {
case <-ctx.Done():
return
case sema <- struct{}{}:
defer func() { <-sema }()
worklist <- getBatch(u)
}
})
}
}
}
cancel()
wg.Wait()
}
func getBatch(u url.URL) []url.URL {
doc, err := fetch(u)
if err != nil {
log.Print(err)
}
batch := findURLs(u, doc)
return batch
}
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