From 4bd71e70e3530735f470f9328b38c16ddb325ad0 Mon Sep 17 00:00:00 2001
From: Tamer Tas <contact@tmrts.com>
Date: Tue, 12 Apr 2016 06:25:19 +0300
Subject: [PATCH] Rewrite fan-in/out messaging patterns

---
 README.md                              |  4 +--
 fan/fan_in.go                          | 33 ---------------------
 messaging/fan_in.md                    | 40 ++++++++++++++++++++++++++
 fan/fan_out.go => messaging/fan_out.md | 17 +++++++----
 4 files changed, 54 insertions(+), 40 deletions(-)
 delete mode 100644 fan/fan_in.go
 create mode 100644 messaging/fan_in.md
 rename fan/fan_out.go => messaging/fan_out.md (55%)

diff --git a/README.md b/README.md
index ce563ea..3d10126 100644
--- a/README.md
+++ b/README.md
@@ -77,8 +77,8 @@ __Messaging Patterns__:
 
 | Pattern | Description |
 |:-------:| ----------- |
-| [Fan-In](fan/fan_in.go) | Funnels tasks to a work sink (e.g. server) |
-| [Fan-Out](fan/fan_out.go) | Distributes tasks amongs workers |
+| [Fan-In](messaging/fan_in.md) | Funnels tasks to a work sink (e.g. server) |
+| [Fan-Out](messaging/fan_out.md) | Distributes tasks amongs workers (e.g. producer) |
 | [Futures & Promises](futures_promises.go) | Acts as a place-holder of a result that is initally unknown for synchronization purposes |
 | [Publish/Subscribe](messaging/publish_subscribe.md) | Passes information to a collection of recipients who subscribed to a topic |
 | [Push & Pull](push_pull.go) | Distributes messages to multiple workers, arranged in a pipeline |
diff --git a/fan/fan_in.go b/fan/fan_in.go
deleted file mode 100644
index 1d8c035..0000000
--- a/fan/fan_in.go
+++ /dev/null
@@ -1,33 +0,0 @@
-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
-}
diff --git a/messaging/fan_in.md b/messaging/fan_in.md
new file mode 100644
index 0000000..d4b3991
--- /dev/null
+++ b/messaging/fan_in.md
@@ -0,0 +1,40 @@
+Fan-In Messaging Patterns
+===================================
+Fan-In is a messaging pattern used to create a funnel for work amongst workers (clients: source, server: destination).
+
+We can model fan-in using the Go channels.
+
+```go
+// Merge different channels in one channel
+func Merge(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
+}
+```
+
+The `Merge` function converts a list of channels to a single channel by starting a goroutine for each inbound channel that copies the values to the sole outbound channel.
+
+Once all the output goroutines have been started, `Merge` a goroutine is started to close the main channel.
diff --git a/fan/fan_out.go b/messaging/fan_out.md
similarity index 55%
rename from fan/fan_out.go
rename to messaging/fan_out.md
index 862306b..3052319 100644
--- a/fan/fan_out.go
+++ b/messaging/fan_out.md
@@ -1,9 +1,12 @@
-package fan
+Fan-Out Messaging Pattern
+=========================
+Fan-Out is a messaging pattern used for distributing work amongst workers (producer: source, consumers: destination).
 
-// Out implements fan.Out messaging pattern
-// Split a channel into n channels that receive messages
-// in a round-robin fashion.
-func Out(ch <-chan int, n int) []<-chan int {
+We can model fan-out using the Go channels.
+
+```go
+// Split a channel into n channels that receive messages in a round-robin fashion.
+func Split(ch <-chan int, n int) []<-chan int {
 	cs := make([]chan int)
 	for i := 0; i < n; i++ {
 		cs = append(cs, make(chan int))
@@ -38,3 +41,7 @@ func Out(ch <-chan int, n int) []<-chan int {
 
 	return cs
 }
+```
+
+The `Split` function converts a single channel into a list of channels by using 
+a goroutine to copy received values to channels in the list in a round-robin fashion.