Go で同時 HTTP リクエストを最大化するには?

package main

import (
    "fmt"
    "net/http"
    "runtime"
    "sync"
    "time"
)

var (
    reqs       int
    concurrent int
    work       chan *http.Request
    results    chan *http.Response
)

func init() {
    reqs = 1000000
    concurrent = 200
}

func main() {
    runtime.GOMAXPROCS(runtime.NumCPU())
    work = make(chan *http.Request, concurrent)
    results = make(chan *http.Response)
    start := time.Now()

    // Create a semaphore channel to limit concurrency
    sem := make(chan struct{}, concurrent)

    // Create a dispatcher to populate the work channel
    go func() {
        for i := 0; i < reqs; i++ {
            req, _ := http.NewRequest("GET", "http://localhost/", nil)
            work <- req
        }
        close(work) // Signal to workers that no more requests are incoming
    }()

    // Create a worker pool to process requests
    for i := 0; i < concurrent; i++ {
        go func() {
            for req := range work {
                resp, err := http.DefaultClient.Do(req)
                if err != nil {
                    fmt.Println(err)
                }
                results <- resp

                // Release semaphore token to allow another worker to proceed
                <-sem
            }
        }()
    }

    // Consume responses from worker pool
    var (
        conns int64
        totalSize int64
        wg     sync.WaitGroup
    )

    wg.Add(1)
    go func() {
        defer wg.Done()
        for {
            select {
            case resp, ok := <-results:
                if ok {
                    conns++
                    totalSize += resp.ContentLength
                    resp.Body.Close()
                } else {
                    return
                }
            }
        }
    }()

    // Block until all responses are processed
    wg.Wait()

    elapsed := time.Since(start)
    fmt.Printf("Connections:\t%d\nConcurrent:\t%d\nTotal size:\t%d bytes\nElapsed:\t%s\n", conns, concurrent, totalSize, elapsed)
}