Read each file / each line concurrently

concurrent_file_read.go

package main

import (
	"bufio"
	"fmt"
	"os"
	"sync"
    "time"
)
var wg sync.WaitGroup

func main() {
	start := time.Now()
	filenames := []string{
		"one.csv",
		"two.csv",
		"three.csv",
		"four.csv",
		"five.csv",
	}
	for n := range filenames {
		wg.Add(1)
		go func(fn string) {
			defer wg.Done()
			file, err := os.Open(fn)
			if err != nil {
				fmt.Println(err)
			}
			defer file.Close()
			scanner := bufio.NewScanner(file)
			for scanner.Scan() {
				wg.Add(1)
				go process(scanner.Text())
			}
		}(filenames[n])
	}

	wg.Wait()
	fmt.Printf("%v ns\n", time.Since(start).Nanoseconds())
}

func process(text string) {
	defer wg.Done()
	fmt.Println(text)
}