go by example part 3

5-go-by-example/30-non-blocking-channel-.go

@@ -0,0 +1,42 @@
+// Basic sends and receives on channels are blocking
+// use select with a default clause to implement non-blocking
+package main
+
+import "fmt"
+
+func main() {
+	messages := make(chan string)
+	signals := make(chan bool)
+
+	// non-blocking receive
+	// if a value is available on messages then select will take the <-messages case with that value
+	// if not it will immediately take the default case
+	select {
+	case msg := <-messages:
+		fmt.Println("received message", msg)
+	default:
+		fmt.Println("no message received")
+	}
+
+	// non-blocking send
+	// msg cannot be sent to the messages channel, because the channel has no buffer and there is no receiver
+	// Therefore the default case is selected.
+	msg := "hi"
+	select {
+	case messages <- msg:
+		fmt.Println("sent message", msg)
+	default:
+		fmt.Println("no message sent")
+	}
+
+	// use multiple cases above the default clause to implement a multi-way non-blocking select
+	// here non-blocking receives on both messages and signals
+	select {
+	case msg := <-messages:
+		fmt.Println("received message", msg)
+	case sig := <-signals:
+		fmt.Println("received signal", sig)
+	default:
+		fmt.Println("no activity")
+	}
+}