Add concurrency

concurrency/cmd/temperatures/print.go

@@ -0,0 +1,59 @@
+package main
+
+import (
+	"fmt"
+	"sync"
+
+	"github.com/dwrz/talks/concurrency/pkg/weather"
+)
+
+const (
+	// Hardcoded padding for longest city name, Philadelphia.
+	message = "%-12s %.2f°F\n"
+)
+
+func printTemperatures(cities []string) {
+	for _, city := range cities {
+		cityWeather, err := weather.GetCity(city)
+		if err != nil {
+			fmt.Printf(
+				"error getting weather for %s: %v\n", city, err,
+			)
+			continue
+		}
+
+		fmt.Printf(message, city, cityWeather.Temp)
+	}
+}
+
+func printTemperaturesAsync(cities []string) {
+	var weatherReports = make(chan string, len(cities))
+	var wg sync.WaitGroup
+	wg.Add(len(cities))
+
+	for _, city := range cities {
+		go func(city string) {
+			defer wg.Done()
+
+			cityWeather, err := weather.GetCity(city)
+			if err != nil {
+				fmt.Printf(
+					"error getting weather for %s: %v\n",
+					city, err,
+				)
+				return
+			}
+
+			weatherReports <- fmt.Sprintf(
+				message, city, cityWeather.Temp,
+			)
+		}(city)
+	}
+
+	wg.Wait()
+	close(weatherReports)
+
+	for report := range weatherReports {
+		fmt.Print(report)
+	}
+}