Add fan-in/out messaging patterns

fan/fan_in.go

@@ -0,0 +1,33 @@
+package fan
+
+import "sync"
+
+// In implements fan.In messaging pattern
+// Merges different channels in one channel
+func In(cs ...<-chan int) <-chan int {
+	var wg sync.WaitGroup
+
+	out := make(chan int)
+
+	// Start an send goroutine for each input channel in cs. send
+	// copies values from c to out until c is closed, then calls wg.Done.
+	send := func(c <-chan int) {
+		for n := range c {
+			out <- n
+		}
+		wg.Done()
+	}
+
+	wg.Add(len(cs))
+	for _, c := range cs {
+		go send(c)
+	}
+
+	// Start a goroutine to close out once all the send goroutines are
+	// done.  This must start after the wg.Add call.
+	go func() {
+		wg.Wait()
+		close(out)
+	}()
+	return out
+}