update book code

eBook/examples/chapter_14/timer_goroutine.go

@@ -0,0 +1,42 @@
+// default.go
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+func main() {
+	tick := time.Tick(1e8)
+	boom := time.After(5e8)
+	for {
+		select {
+		case <-tick:
+			fmt.Println("tick.")
+		case <-boom:
+			fmt.Println("BOOM!")
+			return
+		default:
+			fmt.Println("    .")
+			time.Sleep(5e7)
+		}
+	}
+}
+/* Output:
+    .
+    .
+tick.
+    .
+    .
+tick.
+    .
+    .
+tick.
+    .
+    .
+tick.
+    .
+    .
+tick.
+BOOM!
+*/