First commit

chapter5/database_server.ex

@@ -0,0 +1,31 @@
+defmodule DatabaseServer do
+  def start do
+    spawn(&loop/0)
+  end
+
+  defp loop do
+    receive do
+      {:run_query, caller, query_def} ->
+        send(caller, {:query_result, run_query(query_def)})
+    end
+
+    loop()
+  end
+
+  defp run_query(query_def) do
+    Process.sleep(2000)
+    "#{query_def} result"
+  end
+
+  def run_async(server_pid, query_def) do
+    send(server_pid, {:run_query, self(), query_def})
+  end
+
+  def get_result do
+    receive do
+      {:query_result, result} -> result
+    after
+      5000 -> {:error, :timeout}
+    end
+  end
+end