问题
I use goroutines achieve http.Get timeout, and then I found that the number has been rising steadily goroutines, and when it reaches 1000 or so, the program will exit
Code:
package main
import (
"errors"
"io/ioutil"
"log"
"net"
"net/http"
"runtime"
"time"
)
// timeout dialler
func timeoutDialler(timeout time.Duration) func(network, addr string) (net.Conn, error) {
return func(network, addr string) (net.Conn, error) {
return net.DialTimeout(network, addr, timeout)
}
}
func timeoutHttpGet(url string) ([]byte, error) {
// change dialler add timeout support && disable keep-alive
tr := &http.Transport{
Dial: timeoutDialler(3 * time.Second),
DisableKeepAlives: true,
}
client := &http.Client{Transport: tr}
type Response struct {
resp []byte
err error
}
ch := make(chan Response, 0)
defer func() {
close(ch)
ch = nil
}()
go func() {
resp, err := client.Get(url)
if err != nil {
ch <- Response{[]byte{}, err}
return
}
defer resp.Body.Close()
body, err := ioutil.ReadAll(resp.Body)
if err != nil {
ch <- Response{[]byte{}, err}
return
}
tr.CloseIdleConnections()
ch <- Response{body, err}
}()
select {
case <-time.After(5 * time.Second):
return []byte{}, errors.New("timeout")
case response := <-ch:
return response.resp, response.err
}
}
func handler(w http.ResponseWriter, r *http.Request) {
_, err := timeoutHttpGet("http://google.com")
if err != nil {
log.Println(err)
return
}
}
func main() {
go func() {
for {
log.Println(runtime.NumGoroutine())
time.Sleep(500 * time.Millisecond)
}
}()
s := &http.Server{
Addr: ":8888",
ReadTimeout: 15 * time.Second,
WriteTimeout: 15 * time.Second,
}
http.HandleFunc("/", handler)
log.Fatal(s.ListenAndServe())
}
http://play.golang.org/p/SzGTMMmZkI
回答1:
Init your chan with 1 instead of 0:
ch := make(chan Response, 1)
And remove the defer block that closes and nils ch.
See: http://blog.golang.org/go-concurrency-patterns-timing-out-and
Here is what I think is happening:
- after the 5s timeout, timeoutHttpGet returns
- the defer statement runs, closing ch and then setting it to nil
- the go routine it started to do the actual fetch finishes and attempts to send its data to ch
- but ch is nil, and so won't receive anything, preventing that statement from finishing, and thus preventing the go routine from finishing
I assume you are setting ch = nil
because before you had that, you would get run-time panics because that's what happens when you attempt to write to a closed channel, as described by the spec.
Giving ch a buffer of 1 means that the fetch go routine can send to it without needing a receiver. If the handler has returned due to timeout, everything will just get garbage collected later on.
来源:https://stackoverflow.com/questions/20990332/golang-http-timeout-and-goroutines-accumulation