Add example29: handle multiple Go channel

Signed-off-by: Bo-Yi Wu <[email protected]>

README.md

@@ -31,6 +31,7 @@ Learning basic [Golang](https://golang.org/) in one day
 * [example25](./example25-traefik-golang-app-lets-encrypt): Running golang app using [traefik & Let's Encrypt & Docker](https://docs.traefik.io/user-guide/docker-and-lets-encrypt/).
 * [example27](./example27-how-to-load-env): How to loads environment variables from `.env`.
 * [example28](./example28-webserver-with-gracefull-shutdown): Go webserver with gracefull shutdown.
+* [example29](./example29-handle-multiple-channel): How to handle multiple Go channel?
 
 [1]:https://github.com/golang/lint
 [2]:https://golang.org/cmd/gofmt/

example29-handle-multiple-channel/answer/main.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"math/rand"
+	"sync"
+	"time"
+)
+
+func main() {
+	outChan := make(chan int, 100)
+	errChan := make(chan error)
+	finishChan := make(chan struct{})
+	wg := sync.WaitGroup{}
+	wg.Add(100)
+	for i := 0; i < 100; i++ {
+		go func(outChan chan<- int, errChan chan<- error, val int, wg *sync.WaitGroup) {
+			defer wg.Done()
+			time.Sleep(time.Duration(rand.Int31n(1000)) * time.Millisecond)
+			fmt.Println("finished job id:", val)
+			outChan <- val
+			if val == 60 {
+				errChan <- errors.New("error in 60")
+			}
+
+		}(outChan, errChan, i, &wg)
+	}
+
+	go func() {
+		wg.Wait()
+		fmt.Println("finish all job")
+		close(finishChan)
+	}()
+
+Loop:
+	for {
+		select {
+		case val := <-outChan:
+			fmt.Println("finished:", val)
+		case err := <-errChan:
+			fmt.Println("error:", err)
+			break Loop
+		case <-finishChan:
+			break Loop
+		case <-time.After(100000 * time.Millisecond):
+			break Loop
+		}
+	}
+}

example29-handle-multiple-channel/main.go

@@ -0,0 +1,22 @@
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"sync"
+	"time"
+)
+
+func main() {
+	wg := sync.WaitGroup{}
+	wg.Add(100)
+	for i := 0; i < 100; i++ {
+		go func(val int, wg *sync.WaitGroup) {
+			time.Sleep(time.Duration(rand.Int31n(1000)) * time.Millisecond)
+			fmt.Println("finished job id:", val)
+			wg.Done()
+		}(i, &wg)
+	}
+
+	wg.Wait()
+}