I was looking up knowledge on how to perform a lot of HTTP requests efficiently, and I came across this answer: https://stackoverflow.com/a/23319730/749851 with this code:
package main
import (
"flag"
"fmt"
"log"
"net/http"
"runtime"
"time"
)
var (
reqs int
max int
)
func init() {
flag.IntVar(&reqs, "reqs", 1000000, "Total requests")
flag.IntVar(&max, "concurrent", 200, "Maximum concurrent requests")
}
type Response struct {
*http.Response
err error
}
// Dispatcher
func dispatcher(reqChan chan *http.Request) {
defer close(reqChan)
for i := 0; i < reqs; i++ {
req, err := http.NewRequest("GET", "http://localhost/", nil)
if err != nil {
log.Println(err)
}
reqChan <- req
}
}
// Worker Pool
func workerPool(reqChan chan *http.Request, respChan chan Response) {
t := &http.Transport{}
for i := 0; i < max; i++ {
go worker(t, reqChan, respChan)
}
}
// Worker
func worker(t *http.Transport, reqChan chan *http.Request, respChan chan Response) {
for req := range reqChan {
resp, err := t.RoundTrip(req)
r := Response{resp, err}
respChan <- r
}
}
// Consumer
func consumer(respChan chan Response) (int64, int64) {
var (
conns int64
size int64
)
for conns < int64(reqs) {
select {
case r, ok := <-respChan:
if ok {
if r.err != nil {
log.Println(r.err)
} else {
size += r.ContentLength
if err := r.Body.Close(); err != nil {
log.Println(r.err)
}
}
conns++
}
}
}
return conns, size
}
func main() {
flag.Parse()
runtime.GOMAXPROCS(runtime.NumCPU())
reqChan := make(chan *http.Request)
respChan := make(chan Response)
start := time.Now()
go dispatcher(reqChan)
go workerPool(reqChan, respChan)
conns, size := consumer(respChan)
took := time.Since(start)
ns := took.Nanoseconds()
av := ns / conns
average, err := time.ParseDuration(fmt.Sprintf("%d", av) + "ns")
if err != nil {
log.Println(err)
}
fmt.Printf("Connections:\t%d
Concurrent:\t%d
Total size:\t%d bytes
Total time:\t%s
Average time:\t%s
", conns, max, size, took, average)
}
I'm coming from node so I don't really understand this "go" code.
What part of it is limiting it to 500 HTTP actions at a time? And is it operating in chunks of 500, waiting until that chunk of 500 is finished then starting a new 500, OR is it just always chugging along adding 1 more once it hits 499, etc.
I see that the "workerPool" func goes over a loop only as many times as the maximum amount of concurrent requests, calling "worker" 500 times, but how does it do the next 500 or even the whole 1 million eventually?
