From b052ed103bb28b18736bc684bbff34d98c8e8181 Mon Sep 17 00:00:00 2001
From: "Ben Sheldon [he/him]" <bensheldon@gmail.com>
Date: Wed, 12 Jan 2022 21:42:00 -0800
Subject: [PATCH] Start async adapters once `ActiveRecord` and `ActiveJob` have
 loaded, potentially before `Rails.application.initialized?` (#483)

---
 lib/good_job.rb              |  2 ++
 lib/good_job/adapter.rb      |  2 +-
 lib/good_job/dependencies.rb | 50 ++++++++++++++++++++++++++++++++++++
 lib/good_job/railtie.rb      | 21 ++++++++++++++-
 4 files changed, 73 insertions(+), 2 deletions(-)
 create mode 100644 lib/good_job/dependencies.rb

diff --git a/lib/good_job.rb b/lib/good_job.rb
index 6237bcfee..bb3eabfa9 100644
--- a/lib/good_job.rb
+++ b/lib/good_job.rb
@@ -18,6 +18,8 @@
 #
 # +GoodJob+ is the top-level namespace and exposes configuration attributes.
 module GoodJob
+  include GoodJob::Dependencies
+
   DEFAULT_LOGGER = ActiveSupport::TaggedLogging.new(ActiveSupport::Logger.new($stdout))
 
   # @!attribute [rw] active_record_parent_class
diff --git a/lib/good_job/adapter.rb b/lib/good_job/adapter.rb
index 40d1bd899..9d2625228 100644
--- a/lib/good_job/adapter.rb
+++ b/lib/good_job/adapter.rb
@@ -27,7 +27,7 @@ class Adapter
     # @param queues [String, nil] determines which queues to execute jobs from when +execution_mode+ is set to +:async+. See {file:README.md#optimize-queues-threads-and-processes} for more details on the format of this string. You can also set this with the environment variable +GOOD_JOB_QUEUES+. Defaults to +"*"+.
     # @param poll_interval [Integer, nil] sets the number of seconds between polls for jobs when +execution_mode+ is set to +:async+. You can also set this with the environment variable +GOOD_JOB_POLL_INTERVAL+. Defaults to +1+.
     # @param start_async_on_initialize [Boolean] whether to start the async scheduler when the adapter is initialized.
-    def initialize(execution_mode: nil, queues: nil, max_threads: nil, poll_interval: nil, start_async_on_initialize: Rails.application.initialized?)
+    def initialize(execution_mode: nil, queues: nil, max_threads: nil, poll_interval: nil, start_async_on_initialize: GoodJob.async_ready?)
       @configuration = GoodJob::Configuration.new(
         {
           execution_mode: execution_mode,
diff --git a/lib/good_job/dependencies.rb b/lib/good_job/dependencies.rb
new file mode 100644
index 000000000..b9ef20649
--- /dev/null
+++ b/lib/good_job/dependencies.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+module GoodJob # :nodoc:
+  # Extends GoodJob module to track Rails boot dependencies.
+  module Dependencies
+    extend ActiveSupport::Concern
+
+    included do
+      # @!attribute [rw] _rails_after_initialize_hook_called
+      #   @!scope class
+      #   Whether Railtie.after_initialize has been called yet (default: +false+).
+      #   This will be set on  but before +Rails.application.initialize?+ is +true+.
+      #   @return [Boolean]
+      mattr_accessor :_rails_after_initialize_hook_called, default: false
+
+      # @!attribute [rw] _active_job_loaded
+      #   @!scope class
+      #   Whether ActiveJob has loaded (default: +false+).
+      #   @return [Boolean]
+      mattr_accessor :_active_job_loaded, default: false
+
+      # @!attribute [rw] _active_record_loaded
+      #   @!scope class
+      #   Whether ActiveRecord has loaded (default: +false+).
+      #   @return [Boolean]
+      mattr_accessor :_active_record_loaded, default: false
+    end
+
+    class_methods do
+      # Whether GoodJob's  has been initialized as of the calling of +Railtie.after_initialize+.
+      # @return [Boolean]
+      def async_ready?
+        Rails.application.initialized? || (
+           _rails_after_initialize_hook_called &&
+           _active_job_loaded &&
+           _active_record_loaded
+         )
+      end
+
+      def start_async_adapters
+        return unless async_ready?
+
+        GoodJob::Adapter.instances
+                        .select(&:execute_async?)
+                        .reject(&:async_started?)
+                        .each(&:start_async)
+      end
+    end
+  end
+end
diff --git a/lib/good_job/railtie.rb b/lib/good_job/railtie.rb
index dcf672a59..859747dc0 100644
--- a/lib/good_job/railtie.rb
+++ b/lib/good_job/railtie.rb
@@ -34,8 +34,27 @@ class Railtie < ::Rails::Railtie
     end
 
     initializer "good_job.start_async" do
+      # This hooks into the hookable places during Rails boot, which is unfortunately not Rails.application.initialized?
+      # If an Adapter is initialized during boot, we want to want to start its async executors once the framework dependencies have loaded.
+      # When exactly that happens is out of our control because gems or application code may touch things earlier than expected.
+      # For example, as of Rails 6.1, if an ActiveRecord model is touched during boot, that triggers ActiveRecord to load,
+      # which touches DestroyAssociationAsyncJob, which loads ActiveJob, which may initialize a GoodJob::Adapter, all of which
+      # happens _before_ ActiveRecord finishes loading. GoodJob will deadlock if an async executor is started in the middle of
+      # ActiveRecord loading.
+
       config.after_initialize do
-        GoodJob::Adapter.instances.each(&:start_async)
+        ActiveSupport.on_load(:active_record) do
+          GoodJob._active_record_loaded = true
+          GoodJob.start_async_adapters
+        end
+
+        ActiveSupport.on_load(:active_job) do
+          GoodJob._active_job_loaded = true
+          GoodJob.start_async_adapters
+        end
+
+        GoodJob._rails_after_initialize_hook_called = true
+        GoodJob.start_async_adapters
       end
     end
   end