Browser pools: Reuse limited number of browsers (memory ⬇️, speed ⬆️) (#86)

Experimental browser pooling. Reuses browsers across test suites.
This limits memory usage and is useful when running feature tests together with regular tests
(high ExUnit `max_cases` concurrency such as the default: 2x number of CPU cores).

Pools are defined up front.
Browsers are launched lazily.

Closes #75

Author: ftes

.github/workflows/elixir.yml

@@ -42,7 +42,7 @@ jobs:
       - name: Install chromium browser
         run: npm exec --prefix priv/static/assets -- playwright install chromium --with-deps --only-shell
       - name: Run tests
-        run: "mix test --warnings-as-errors --max-cases 1 || if [[ $? = 2 ]]; then PW_TRACE=true mix test --max-cases 1 --failed; else false; fi"
+        run: "mix test --warnings-as-errors || if [[ $? = 2 ]]; then PW_TRACE=true mix test --failed; else false; fi"
       - name: Fail if screenshot on exit failed
         run: |
           if ! ls screenshots/PhoenixTest.Playwright.CaseTest.test__tag__screenshot_saves_screenshot_on_test_exit* >/dev/null 2>&1; then

lib/phoenix_test/playwright/browser_pool.ex

@@ -0,0 +1,138 @@
+defmodule PhoenixTest.Playwright.BrowserPool do
+  @moduledoc """
+  Experimental browser pooling. Reuses browsers across test suites.
+  This limits memory usage and is useful when running feature tests together with regular tests
+  (high ExUnit `max_cases` concurrency such as the default: 2x number of CPU cores).
+
+  Pools are defined up front.
+  Browsers are launched lazily.
+
+  Usage:
+
+  ```ex
+  # test/test_helper.exs
+  {:ok, _} =
+    Supervisor.start_link(
+      [
+        {PhoenixTest.Playwright.BrowserPool, name: :normal_chromium, size: System.schedulers_online(), browser: :chromium},
+        {PhoenixTest.Playwright.BrowserPool, name: :slow_chromium, size: 4, browser: :chromium, slow_mo: 100},
+      ],
+      strategy: :one_for_one
+    )
+
+  # configure pool per test module
+  # test/my_test.exs
+  defmodule PhoenixTest.PlaywrightBrowserPoolTest do
+    use PhoenixTest.Playwright.Case,
+      async: true,
+      browser_pool: :normal_chromium
+  end
+
+  # or configure globally
+  # test/test.exs
+  config :phoenix_test,
+    playwright: [
+      browser_pool: :normal_chromium,
+      browser_pool_checkout_timeout: to_timeout(minute: 10)
+    ]
+  ```
+  """
+
+  use GenServer
+
+  alias __MODULE__, as: State
+  alias PhoenixTest.Playwright
+
+  defstruct [
+    :size,
+    :config,
+    available: [],
+    in_use: %{},
+    waiting: []
+  ]
+
+  @type pool :: GenServer.server()
+  @type browser_id :: binary()
+
+  ## Public
+
+  @spec checkout(pool()) :: browser_id()
+  def checkout(pool) do
+    timeout = Playwright.Config.global(:browser_pool_checkout_timeout)
+    GenServer.call(pool, :checkout, timeout)
+  end
+
+  ## Internal
+
+  @doc false
+  def start_link(opts) do
+    {name, opts} = Keyword.pop!(opts, :name)
+    {size, opts} = Keyword.pop!(opts, :size)
+
+    GenServer.start_link(__MODULE__, %State{size: size, config: opts}, name: name)
+  end
+
+  @impl GenServer
+  def init(state) do
+    # Trap exits so we can clean up browsers on shutdown
+    Process.flag(:trap_exit, true)
+    {:ok, state}
+  end
+
+  @impl GenServer
+  def handle_call(:checkout, from, state) do
+    cond do
+      length(state.available) > 0 ->
+        browser_id = hd(state.available)
+        state = do_checkout(state, from, browser_id)
+        {:reply, browser_id, state}
+
+      map_size(state.in_use) < state.size ->
+        browser_id = launch(state.config)
+        state = do_checkout(state, from, browser_id)
+        {:reply, browser_id, state}
+
+      true ->
+        state = Map.update!(state, :waiting, &(&1 ++ [from]))
+        {:noreply, state}
+    end
+  end
+
+  @impl GenServer
+  def handle_info({:DOWN, ref, :process, pid, _reason}, state) do
+    case Enum.find_value(state.in_use, fn {browser_id, tracked} -> tracked == {pid, ref} and browser_id end) do
+      nil -> {:noreply, state}
+      browser_id -> {:noreply, do_checkin(state, browser_id)}
+    end
+  end
+
+  defp launch(config) do
+    config = config |> Playwright.Config.validate!() |> Keyword.take(Playwright.Config.setup_all_keys())
+
+    {type, config} = Keyword.pop!(config, :browser)
+    Playwright.Connection.launch_browser(type, config)
+  end
+
+  defp do_checkout(state, from, browser_id) do
+    {from_pid, _tag} = from
+
+    state
+    |> Map.update!(:available, &(&1 -- [browser_id]))
+    |> Map.update!(:in_use, &Map.put(&1, browser_id, {from_pid, Process.monitor(from_pid)}))
+  end
+
+  defp do_checkin(state, browser_id) do
+    {{_from_pid, ref}, in_use} = Map.pop(state.in_use, browser_id)
+    Process.demonitor(ref, [:flush])
+    state = %{state | in_use: in_use, available: [browser_id | state.available]}
+
+    case state.waiting do
+      [from | rest] ->
+        GenServer.reply(from, browser_id)
+        %{do_checkout(state, from, browser_id) | waiting: rest}
+
+      _ ->
+        state
+    end
+  end
+end

lib/phoenix_test/playwright/case.ex

@@ -60,7 +60,12 @@ defmodule PhoenixTest.Playwright.Case do
   def do_setup_all(context) do
     keys = Playwright.Config.setup_all_keys()
     config = context |> Map.take(keys) |> Playwright.Config.validate!() |> Keyword.take(keys)
-    [browser_id: launch_browser(config)]
+
+    if pool = config[:browser_pool] do
+      [browser_id: Playwright.BrowserPool.checkout(pool)]
+    else
+      [browser_id: launch_browser(config)]
+    end
   end
 
   @doc """

lib/phoenix_test/playwright/config.ex

@@ -68,6 +68,16 @@ schema =
       default: to_timeout(second: 2),
       type: :non_neg_integer
     ],
+    browser_pool_checkout_timeout: [
+      default: to_timeout(minute: 1),
+      type: :non_neg_integer
+    ],
+    browser_pool: [
+      default: nil,
+      type: :any,
+      doc:
+        "Reuse a browser from this pool instead of launching a new browser per test suite. See `PhoenixTest.Playwright.BrowserPool`."
+    ],
     slow_mo: [
       default: to_timeout(second: 0),
       type: :non_neg_integer
@@ -108,7 +118,7 @@ schema =
     ]
   )
 
-setup_all_keys = ~w(browser browser_launch_timeout executable_path headless slow_mo)a
+setup_all_keys = ~w(browser_pool browser browser_launch_timeout executable_path headless slow_mo)a
 setup_keys = ~w(accept_dialogs screenshot trace browser_context_opts browser_page_opts)a
 
 defmodule PhoenixTest.Playwright.Config do

mix.exs

@@ -96,7 +96,7 @@ defmodule PhoenixTestPlaywright.MixProject do
         "credo",
         "compile --warnings-as-errors",
         "assets.build",
-        "test --warnings-as-errors --max-cases 1"
+        "test --warnings-as-errors"
       ]
     ]
   end

test/phoenix_test/playwright_browser_pool_test.exs

@@ -0,0 +1,12 @@
+defmodule PhoenixTest.PlaywrightBrowserPoolTest do
+  use PhoenixTest.Playwright.Case,
+    async: true,
+    browser_pool: :chromium,
+    parameterize: Enum.map(1..100, &%{index: &1})
+
+  test "navigates to page", %{conn: conn} do
+    conn
+    |> visit("/page/index")
+    |> assert_has("h1", text: "Main page")
+  end
+end

test/test_helper.exs

@@ -1,7 +1,13 @@
 ExUnit.start(capture_log: true)
 
 {:ok, _} =
-  Supervisor.start_link([{Phoenix.PubSub, name: PhoenixTest.PubSub}], strategy: :one_for_one)
+  Supervisor.start_link(
+    [
+      {Phoenix.PubSub, name: PhoenixTest.PubSub},
+      {PhoenixTest.Playwright.BrowserPool, name: :chromium, size: System.schedulers_online(), browser: :chromium}
+    ],
+    strategy: :one_for_one
+  )
 
 {:ok, _} = PhoenixTest.Endpoint.start_link()