package main
import (
"fmt"
"io"
"log"
"net/http"
"sync"
"time"
)
type result struct {
value interface{}
err error
}
type Memo struct {
requests chan request
}
type request struct {
key string
response chan<- result
}
type entry struct {
res result
ready chan struct{}
}
func httpGetBody(url string) (interface{}, error) {
resp, err := http.Get(url)
if err != nil {
return nil, err
}
defer resp.Body.Close()
return io.ReadAll(resp.Body)
}
type Func func(key string) (interface{}, error)
func New(f Func) *Memo {
memo := &Memo{requests: make(chan request)}
go memo.server(f)
return memo
}
func (memo *Memo) Get(key string) (value interface{}, err error) {
response := make(chan result)
memo.requests <- request{key, response}
res := <-response
return res.value, res.err
}
func (memo *Memo) server(f Func) {
cache := make(map[string]*entry)
for req := range memo.requests {
e := cache[req.key]
if e == nil {
e = &entry{ready: make(chan struct{})}
cache[req.key] = e
go e.call(f, req.key)
}
go e.deliver(req.response)
}
}
func (e *entry) call(f Func, key string) {
e.res.value, e.res.err = f(key)
close(e.ready)
}
func (e *entry) deliver(response chan<- result) {
<-e.ready
response <- e.res
}
func incomingURLs() <-chan string {
ch := make(chan string)
go func() {
for _, url := range []string{
"https://golang.org", "https://godoc.org",
"https://play.golang.org", "http://gopl.io",
"https://golang.org", "https://godoc.org",
"https://play.golang.org", "http://gopl.io",
} {
ch <- url
}
close(ch)
}()
return ch
}
func main() {
m := New(httpGetBody)
var n sync.WaitGroup
for url := range incomingURLs() {
n.Add(1)
go func(url string) {
start := time.Now()
_, err := m.Get(url)
if err != nil {
log.Print(err)
}
fmt.Printf("%s, %s \n",
url, time.Since(start))
n.Done()
}(url)
}
n.Wait()
}
package main
import (
"fmt"
"io"
"log"
"net/http"
"sync"
"time"
)
type entry struct {
res result
ready chan struct{}
}
func httpGetBody(url string) (interface{}, error) {
resp, err := http.Get(url)
if err != nil {
return nil, err
}
defer resp.Body.Close()
return io.ReadAll(resp.Body)
}
type Func func(key string) (interface{}, error)
type result struct {
value interface{}
err error
}
type Memo struct {
f Func
mu sync.Mutex
cache map[string]*entry
}
func New(f Func) *Memo {
return &Memo{f: f, cache: make(map[string]*entry)}
}
func (memo *Memo) Get(key string) (value interface{}, err error) {
memo.mu.Lock()
e := memo.cache[key]
if err == nil {
e = &entry{ready: make(chan struct{})}
memo.cache[key] = e
memo.mu.Unlock()
e.res.value, e.res.err = memo.f(key)
close(e.ready)
} else {
memo.mu.Unlock()
<-e.ready
}
return e.res.value, e.res.err
}
func incomingURLs() <-chan string {
ch := make(chan string)
go func() {
for _, url := range []string{
"https://golang.org", "https://godoc.org",
"https://play.golang.org", "http://gopl.io",
"https://golang.org", "https://godoc.org",
"https://play.golang.org", "http://gopl.io",
} {
ch <- url
}
close(ch)
}()
return ch
}
func main() {
m := New(httpGetBody)
var n sync.WaitGroup
for url := range incomingURLs() {
n.Add(1)
go func(url string) {
start := time.Now()
_, err := m.Get(url)
if err != nil {
log.Print(err)
}
fmt.Printf("%s, %s \n",
url, time.Since(start))
n.Done()
}(url)
}
n.Wait()
}
