multi file read example code

multifile.go

package main

import (
	"bufio"
	"flag"
	"fmt"
	"time"
	"log"
	"io"
	"os"
	"path"
)

type data_t struct {
	Buf []byte
	N   int
}

func usage() {
	_, exeName := path.Split(os.Args[0])
	fmt.Fprintf(os.Stderr, `Usage: %s <input_files>`, exeName)
	flag.PrintDefaults()
}

func Reader(fname string, chQuit chan bool, out chan data_t) error {
	fmt.Println("Reader for", fname)
	f, err := os.Open(fname)
	if err != nil {
		log.Fatalln(err)
	}
	defer f.Close()
	r := bufio.NewReader(f)
	prevReadTime := time.Now()
F:
	for {
		select {
		case <-chQuit:
			break F
		default:
			var v data_t
			v.Buf = make([]byte,1024)
			readTime := time.Now()
			v.N, err = r.Read(v.Buf)
			if err != nil && err != io.EOF {
				log.Fatalln(err)
			}
			if readTime.Sub(prevReadTime) < 3 * time.Second {
				if v.N == 0 {
					time.Sleep(1000 * time.Millisecond) // 0.5 s
				} else {
					prevReadTime = readTime
					fmt.Println(fname, "read", v.N, "bytes")
					out <- v
				}
			} else {
				fmt.Println("Timeout for 3 seconds", readTime.Sub(prevReadTime))
				break F
			}
		}
	}
	return nil
}

func main() {

	log.SetFlags(log.Lshortfile)
	flag.Usage = usage
	flag.Parse()
	if flag.NArg() == 0 {
		usage()
		os.Exit(1)
	}

	chData := make(chan data_t)

	nLen := int(flag.NArg())
	chQuit := make([]chan bool, nLen)
	for i, fname := range flag.Args() {
		go Reader(fname, chQuit[i], chData)
	}

	const timeoutNs = 20e9

F:
	for {
		select {
		case data := <-chData:
			fmt.Println("data=", data.Buf[:data.N])
		case <-time.After(timeoutNs):
			fmt.Println("Timeout")
			break F
		}

	}

	// Bug here, will cause all thread sleeping
	for i := range flag.Args() {
		chQuit[i] <- true
	}

}