add examples about goroutine and wait group

1-echo-text/main.go

@@ -0,0 +1,28 @@
+package main
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"time"
+)
+
+/*
+	@Ref: https://livebook.manning.com/book/go-in-practice/chapter-3/65
+	`os.Stdin` and `os.Stdout` will be used as the system input and output. It's great.
+
+
+*/
+
+func main() {
+	go echo(os.Stdin, os.Stdout)
+
+	time.Sleep(30 * time.Second)
+
+	fmt.Println("Time out.")
+	os.Exit(0)
+}
+
+func echo(in io.Reader, out io.Writer) {
+	io.Copy(out, in)
+}

2-compress-file/main.go

@@ -0,0 +1,67 @@
+package main
+
+import (
+	"compress/gzip"
+	"fmt"
+	"io"
+	"os"
+	"sync"
+)
+
+/*
+	@Ref: https://livebook.manning.com/book/go-in-practice/chapter-3/65
+	1. Practice gzip compress
+	2. How to use wait group
+	3. os.Args[1:] can stream in multiple files to the program without writing a walk function. Command: go run main.go ./testdata/*
+
+*/
+func main() {
+
+	// Single thread
+	// for _, file := range os.Args[1:] {
+
+	// 	err := compress(file)
+	// 	if err != nil {
+	// 		os.Exit(0)
+	// 	}
+	// }
+
+	// Multi threads
+	wg := sync.WaitGroup{}
+	var (
+		i    int
+		file string
+	)
+	for i, file = range os.Args[1:] {
+		wg.Add(1)
+		go func(filename string) {
+			compress(filename)
+			wg.Done()
+		}(file)
+	}
+
+	wg.Wait()
+	fmt.Printf("Compressed %d files\n", i+1)
+}
+
+func compress(filename string) error {
+	in, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+
+	defer in.Close()
+
+	out, err := os.Create(filename + ".gz")
+	if err != nil {
+		return err
+	}
+
+	defer out.Close()
+
+	gzout := gzip.NewWriter(out)
+	_, err = io.Copy(gzout, in)
+	gzout.Close()
+
+	return err
+}