added ping pong example

concurrency/pingpong/main.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+type Ball struct{ hits int }
+
+func main() {
+	table := make(chan *Ball)
+	go player("ping", table)
+	go player("pong", table)
+	table <- new(Ball) // game on; toss the ball
+	time.Sleep(1 * time.Second)
+	<-table // game over; grab the ball
+}
+
+func player(name string, table chan *Ball) {
+	for {
+		ball := <-table
+		ball.hits++
+		fmt.Println(name, ball.hits)
+		time.Sleep(100 * time.Millisecond)
+		table <- ball
+	}
+}