good good study, day day up!

vendor/gopl.io/ch8/countdown3/countdown.go

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+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 246.
+
+// Countdown implements the countdown for a rocket launch.
+package main
+
+// NOTE: the ticker goroutine never terminates if the launch is aborted.
+// This is a "goroutine leak".
+
+import (
+	"fmt"
+	"os"
+	"time"
+)
+
+//!+
+
+func main() {
+	// ...create abort channel...
+
+	//!-
+
+	abort := make(chan struct{})
+	go func() {
+		os.Stdin.Read(make([]byte, 1)) // read a single byte
+		abort <- struct{}{}
+	}()
+
+	//!+
+	fmt.Println("Commencing countdown.  Press return to abort.")
+	tick := time.Tick(1 * time.Second)
+	for countdown := 10; countdown > 0; countdown-- {
+		fmt.Println(countdown)
+		select {
+		case <-tick:
+			// Do nothing.
+		case <-abort:
+			fmt.Println("Launch aborted!")
+			return
+		}
+	}
+	launch()
+}
+
+//!-
+
+func launch() {
+	fmt.Println("Lift off!")
+}