如何正确设置CPU密集型Web终结点

Question

我需要一个网络路由，该网络路由使用.jpg和来自磁盘的多个.png文件生成映像，并将其返回给客户端。由于此操作会占用大量CPU，因此我决定尝试使用go getComposed()和简单的img := getComposed()，但似乎两种方法都可以同时使用。为什么这样？以及如何提高此具体案例的性能？

package main

import (
    "bytes"
    "fmt"
    "github.com/valyala/fasthttp"
    "image"
    "image/draw"
    "image/jpeg"
    "image/png"
    "log"
    "os"
    "strconv"
    "time"
)

func getImage(path string, ext string) image.Image {
    opened, err := os.Open(path)
    defer opened.Close()

    if err != nil {
        log.Fatalf("failed to open: %s", err)
    }

    switch ext {
        default:
            fallthrough
        case "png":
            img, _ := png.Decode(opened)
            return img
        case "jpg":
            img, _ := jpeg.Decode(opened)
            return img

    }
}

func getComposed() image.Image {
    start := time.Now()

    bg := getImage("bgImages/bg.1000.jpg", "jpg")
    bgBounds := bg.Bounds()

    result := image.NewRGBA(bgBounds)
    draw.Draw(result, bgBounds, bg, image.ZP, draw.Src)

    dir, _ := os.Open("composeImages")
    files, _ := dir.Readdir(-1)

    for _, file := range files {
        composedPng := getImage("composeImages/" + file.Name(), "png")
        draw.Draw(result, composedPng.Bounds(), composedPng, image.ZP, draw.Over)
    }

    elapsed := time.Since(start)
    fmt.Println("IMAGE Elapsed %s", elapsed)
    return result
}

func handler(ctx *fasthttp.RequestCtx) {
    start := time.Now()

    //img := getComposed()
    // OR
    messages := make(chan image.Image)
    go func() { messages <- getComposed() }()
    img := <-messages

    buffer := new(bytes.Buffer)
    if err := jpeg.Encode(buffer, img, nil); err != nil {
        log.Println("unable to encode image.")
    }

    ctx.SetContentType("image/jpeg")
    ctx.Response.Header.Set("Content-Length", strconv.Itoa(len(buffer.Bytes())))

    elapsed := time.Since(start)
    fmt.Println("SERVER Elapsed %s", elapsed)

    if _, err := ctx.Write(buffer.Bytes()); err != nil {
        log.Println("unable to write image.")
    }
}

func main() {
    fasthttp.ListenAndServe(":8002", handler)
}