Here’s a single file demo implementation:
# Single-file Phoenix LiveView demo showing how to batch events to reduce/control the flow of UI updates.
#
# Run with `elixir batcher_demo.exs`, then open a browser at http://localhost:5001/.
#
# For comparison, the "inc" event is batched while the "dec" event is not.
#
# References
#
# https://github.com/phoenixframework/phoenix_live_view/blob/main/.github/single-file-samples/main.exs
# https://elixirforum.com/t/optimizing-liveview-for-realtime-applications-by-marlus-saraiva-elixirconf-eu-2023/59265?u=rhcarvalho
# https://elixirforum.com/t/batching-pubsub-events-to-throttle-socket-updates/64658/2?u=rhcarvalho
Application.put_env(:sample, Example.Endpoint,
http: [ip: {127, 0, 0, 1}, port: 5001],
server: true,
live_view: [signing_salt: "aaaaaaaa"],
secret_key_base: String.duplicate("a", 64)
)
Mix.install([
{:plug_cowboy, "~> 2.5"},
{:jason, "~> 1.0"},
{:phoenix, "~> 1.7"},
{:phoenix_live_view, "~> 0.20.17"}
])
# build the LiveView JavaScript assets (this needs mix and npm available in your path!)
path = Phoenix.LiveView.__info__(:compile)[:source] |> Path.dirname() |> Path.join("../")
System.cmd("mix", ["deps.get"], cd: path, into: IO.binstream())
System.cmd("npm", ["install"], cd: Path.join(path, "./assets"), into: IO.binstream())
System.cmd("mix", ["assets.build"], cd: path, into: IO.binstream())
defmodule Example.ErrorView do
def render(template, _), do: Phoenix.Controller.status_message_from_template(template)
end
defmodule Example.HomeLive do
use Phoenix.LiveView, layout: {__MODULE__, :live}
on_mount({Batcher, {"inc", handler: __MODULE__, max_size: 5, timeout: 2000}})
@behaviour Batcher
def mount(_params, _session, socket) do
{:ok, assign(socket, :count, 0)}
end
def render("live.html", assigns) do
~H"""
<script src="/assets/phoenix/phoenix.js"></script>
<script src="/assets/phoenix_live_view/phoenix_live_view.js"></script>
<%!-- uncomment to use enable tailwind --%>
<%!-- <script src="https://cdn.tailwindcss.com"></script> --%>
<script>
let liveSocket = new window.LiveView.LiveSocket("/live", window.Phoenix.Socket)
liveSocket.connect()
</script>
<style>
* { font-size: 1.1em; }
</style>
<%= @inner_content %>
"""
end
def render(assigns) do
~H"""
<%= @count %>
<button phx-click="inc">+</button>
<button phx-click="dec">-</button>
"""
end
def handle_batch("inc", batch, socket) do
{:noreply, assign(socket, :count, socket.assigns.count + length(batch))}
end
def handle_event("dec", _params, socket) do
{:noreply, assign(socket, :count, socket.assigns.count - 1)}
end
end
defmodule Batcher do
@callback handle_batch(
event :: binary(),
batch :: [Phoenix.LiveView.unsigned_params()],
socket :: Phoenix.LiveView.Socket.t()
) ::
{:noreply, Phoenix.LiveView.Socket.t()}
| {:reply, map(), Phoenix.LiveView.Socket.t()}
def on_mount({event, opts}, _params, _session, socket) do
handler = Keyword.fetch!(opts, :handler)
max_size = Keyword.fetch!(opts, :max_size)
timeout = Keyword.fetch!(opts, :timeout)
socket =
socket
|> Phoenix.LiveView.attach_hook("batcher_event", :handle_event, fn
^event, params, socket ->
socket =
case add_to_batch(socket, event, params) do
{socket, batch} when length(batch) == max_size ->
flush_batch(socket, event, handler)
{socket, _} ->
reschedule_flush_batch(socket, event, timeout)
end
{:halt, socket}
_event, _params, socket ->
{:cont, socket}
end)
|> Phoenix.LiveView.attach_hook("batcher_info", :handle_info, fn
{:flush_batch, event}, socket ->
socket =
case get_batch(socket, event) do
batch when length(batch) > 0 -> flush_batch(socket, event, handler)
_ -> socket
end
{:halt, socket}
_msg, socket ->
{:cont, socket}
end)
{:cont, socket}
end
defp add_to_batch(socket, event, params) do
# note: batch events are in reverse order
batch = [params | get_batch(socket, event)]
{put_batch(socket, event, batch), batch}
end
defp flush_batch(socket, event, handler) do
socket = cancel_timeout(socket, event)
batch = get_batch(socket, event) |> Enum.reverse()
{:noreply, socket} = handler.handle_batch(event, batch, socket)
socket |> put_batch(event, [])
end
defp reschedule_flush_batch(socket, event, timeout) do
socket = cancel_timeout(socket, event)
timeout_ref = Process.send_after(self(), {:flush_batch, event}, timeout)
socket |> put_timeout_ref(event, timeout_ref)
end
defp cancel_timeout(socket, event) do
if timeout_ref = get_timeout_ref(socket, event) do
Process.cancel_timer(timeout_ref)
end
socket |> put_timeout_ref(event, nil)
end
defp get_batch(socket, event) do
socket.private[{__MODULE__, event, :batch}] || []
end
def get_timeout_ref(socket, event) do
socket.private[{__MODULE__, event, :timeout_ref}]
end
defp put_batch(socket, event, batch) do
socket |> Phoenix.LiveView.put_private({__MODULE__, event, :batch}, batch)
end
defp put_timeout_ref(socket, event, timeout_ref) do
socket |> Phoenix.LiveView.put_private({__MODULE__, event, :timeout_ref}, timeout_ref)
end
end
defmodule Example.Router do
use Phoenix.Router
import Phoenix.LiveView.Router
pipeline :browser do
plug(:accepts, ["html"])
end
scope "/", Example do
pipe_through(:browser)
live("/", HomeLive, :index)
end
end
defmodule Example.Endpoint do
use Phoenix.Endpoint, otp_app: :sample
socket("/live", Phoenix.LiveView.Socket)
plug(Plug.Static, from: {:phoenix, "priv/static"}, at: "/assets/phoenix")
plug(Plug.Static, from: {:phoenix_live_view, "priv/static"}, at: "/assets/phoenix_live_view")
plug(Example.Router)
end
{:ok, _} = Supervisor.start_link([Example.Endpoint], strategy: :one_for_one)
Process.sleep(:infinity)
(also available as a GitHub Gist: Phoenix LiveView event batching · GitHub)
