Hi! I’ve been studying concurrency models with elixir. Now, I want to develop a ChatRoom, where users can Join, post messages, and disconnect themselves using threads and mutex in elixir. So far I have developed the model for entering new users and disconnect them. However, I have put some “prints” to see how its working, but they are not showing when I run the program. This is the code,

defmodule MyMutex do
  @mutex :free

  def lock(:free) do
    {:ok, :locked}
  end

  def lock(:locked) do
    {:error, :already_locked}
  end

  def unlock(:locked) do
    :ok
  end

  def unlock(:free) do
    {:error, :not_locked}
  end
end

defmodule Chat do

  defstruct users: [], messages: [], mutex: MyMutex

  def start_link() do
    {:ok, pid} = Task.start_link(fn -> action(%__MODULE__{}) end)
  end

  defp action(chat) do
    receive do
    {:join, :user} ->
      chat = new_user(chat, :user)
      action(chat)
    #{:post, user} ->
    #  chat = post_message(chat, user)
    #  action(chat)
    {:disconnect, user} ->
      chat = disconnect_user(chat, user)
      action(chat)
    {:users_chat} ->
      post_all_users(chat)
      action(chat)
    end
  end

  defp post_all_users(chat) do
    Enum.each(chat.users, fn user ->
      "User:"
    end)
  end

  defp post_message_to_all(chat, message) do
    Enum.each(chat.users, fn user ->
      IO.puts("Message from server: #{message} (Sent to: #{user})")
    end)
  end

  defp new_user(chat ,user) do
    {:ok, mutex} = MyMutex.lock(chat.mutex)
    updated_chat = %{ chat | users: chat.users ++ [user], mutex: mutex }
    IO.puts("Entering the chat: #{user}")
    MyMutex.unlock(mutex)
    post_message_to_all(updated_chat, "#{user} has joined the chat.")
    updated_chat
  end

  defp disconnect_user(chat, user) do
    {:ok, mutex} = MyMutex.lock(chat.mutex)
    chat = %{chat | users: List.delete(chat.users, user),
            mutex: mutex}
    IO.puts("The user #{user} has leaved the chat")
    MyMutex.lock(mutex)
    chat
  end

end

Thanks in Advice