Add exercise 3 from chapter 15

Author: Bernard Pietraga

chapter_15/nodes_3.ex

@@ -0,0 +1,47 @@
+defmodule Ticker do
+  @interval 2000
+  @name :ticker
+
+  def start do
+    pid = spawn(__MODULE__, :generator, [[]])
+    :global.register_name(@name, pid)
+  end
+
+  def register(client_pid) do
+    send :global.whereis_name(@name), {:register, client_pid}
+  end
+
+  def generator(clients) do
+    receive do
+      {:register, pid} ->
+        IO.puts "registering: #{IO.inspect(pid)}"
+        generator([pid | clients])
+    after
+      @interval ->
+        case clients do
+          [] ->
+            generator(clients)
+
+          [client | rest_of_clients] ->
+            IO.puts "tick to: #{IO.inspect(clients)}"
+            send client, {:tick}
+            generator(:lists.append(rest_of_clients, [client]))
+        end
+    end
+  end
+end
+
+defmodule Client do
+  def start do
+    pid = spawn(__MODULE__, :receiver, [])
+    Ticker.register(pid)
+  end
+
+  def receiver do
+    receive do
+      {:tick} ->
+        IO.puts "tock in client"
+        receiver()
+    end
+  end
+end