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package main
import (
"context"
"fmt"
"log"
"net/url"
"sync"
)
func classic(startURL url.URL, maxConcurrency, maxURLs, maxDepth int) {
worklist := make(chan []packet)
var numPendingSends int
numPendingSends++
go func() {
startPacket := packet{startURL, 0}
worklist <- []packet{startPacket}
}()
// Crawl the web concurrently. Map URLs to their depth (i.e
// how many links we have to work through to find the URL.)
seen := make(map[url.URL]int)
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 _, p := range batch {
if _, ok := seen[p.url]; !ok {
fmt.Printf("%d. %s\n", count, &p)
count++
seen[p.url] = p.depth
if len(seen) == maxURLs {
break loop
}
// Track maxDepth here. A maxDepth
// greater than zero means a finite
// maxDepth value. If the packets
// we're seeing reach that depth,
// don't use their URLs to spawn new
// fetches.
if maxDepth > 0 && p.depth == maxDepth {
continue
}
numPendingSends++
wg.Go(func() {
sema <- struct{}{}
defer func() { <-sema }()
batch := getBatch(p.url)
ps := convertToPackets(batch, p.depth+1)
select {
case <-ctx.Done():
return
case worklist <- ps:
}
})
}
}
}
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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