added unbuffed example

channel/unbuffed/main.go

@@ -0,0 +1,33 @@
+package main
+
+import (
+	"fmt"
+	"time"
+)
+
+// https://nanxiao.gitbooks.io/golang-101-hacks/content/posts/unbuffered-and-buffered-channels.html
+// After the main goroutine is launched, it will sleep immediately("Main goroutine sleeps 2 seconds" is printed),
+// and this will cause main goroutine relinquishes the CPU to the func goroutine("Func goroutine begins sending data" is printed).
+// But since the main goroutine is sleeping and can't receive data from the channel,
+// so ch <- 1 operation in func goroutine can't complete until d := <- ch in main goroutine is executed(The final 3 logs are printed).
+func main() {
+
+	ch := make(chan int)
+
+	go func(ch chan int) {
+		fmt.Println("Func goroutine begins sending data")
+		// sender will block on the channel until the receiver receives the data from the channel
+		ch <- 1
+		fmt.Println("Func goroutine ends sending data")
+	}(ch)
+
+	fmt.Println("Main goroutine sleeps 2 seconds")
+	time.Sleep(time.Second * 2)
+
+	fmt.Println("Main goroutine begins receiving data")
+	// the receiver will also block on the channel until sender sends data into the channel.
+	d := <-ch
+	fmt.Println("Main goroutine received data:", d)
+
+	time.Sleep(time.Second)
+}