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|
package main
import (
"context"
"fmt"
"net/url"
"sync"
)
/*
main goroutine:
- manages urls channel.
*/
func workers(startURL url.URL, maxConcurrency, maxURLs int) {
worklist := make(chan []url.URL)
// Unseen URLs.
urls := make(chan url.URL)
go func() {
worklist <- []url.URL{startURL}
}()
var wg sync.WaitGroup
ctx, cancel := context.WithCancel(context.Background())
// Create maxConcurrency worker goroutines to demultiplex from
// the urls channel (unseen links.)
for i := range maxConcurrency {
wg.Go(func() {
for u := range urls {
batch := getBatch(u)
select {
case <-ctx.Done():
fmt.Printf("exiting early %d\n", i+1)
return
default:
go func() { worklist <- batch }()
}
}
fmt.Printf("terminating %d\n", i+1)
})
}
// The main goroutine deduplicates worklist items and sends
// unseen ones to the crawlers in a fan-out fashion.
seen := make(map[url.URL]bool)
count := 1
loop:
for batch := range 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
}
urls <- u
}
}
}
close(urls)
cancel()
wg.Wait()
}
|
