Add concurrency

concurrency/cmd/temperatures/main.go

@@ -0,0 +1,40 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+var cities = []string{
+	"Chicago",
+	"Dallas",
+	"Houston",
+	"Los Angeles",
+	"New York",
+	"Philadelphia",
+	"Phoenix",
+	"San Antonio",
+	"San Diego",
+	"San Jose",
+}
+
+func main() {
+	now := time.Now()
+
+	printTemperatures(cities)
+
+	fmt.Printf(
+		"\nTook %v to get temperatures sequentially.\n\n",
+		time.Since(now),
+	)
+
+	// Reset the timer.
+	now = time.Now()
+
+	printTemperaturesAsync(cities)
+
+	fmt.Printf(
+		"\nTook %v to get temperatures concurrently.\n\n",
+		time.Since(now),
+	)
+}