Eagerly preload framework base classes#752
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rafaelfranca merged 1 commit intoMay 1, 2026
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After `config/environment` is loaded, eagerly autoload framework base classes (`ActionMailer::Base`, `ActionController::Base`, `ActionController::API`) so their `ActiveSupport.on_load` hooks fire in the parent process. Those classes shouldn't change and sometimes have side effects when loaded, although the biggest one is getting fixed in Rails (see rails/rails#57269), it won't hurt to still preload those classes so they don't get loaded on each fork again.
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Spring::Application#servecallsRails.application.reloaders.any?(&:updated?)before forking. ActionView'sCacheExpiry::ViewReloader#updated?lazily builds aFileUpdateCheckerfrom whatever view paths are registered at that moment (lazy-init contract from rails/rails#51308).Engines register view paths via
prepend_view_pathinsideon_load(:action_mailer)/:action_controller_baseblocks. In a fresh preload nothing has referenced those framework classes yet, sodirs_to_watchis empty when the probe runs — pinning the watcher empty and triggering a fullFileUpdateCheckerrebuild on everyprepend_view_pathin each fork.Preloading the framework classes (not
Application*, per Rafael's suggestion, framework code is never reloaded, app namespace is) targets theon_loadhooks directly and avoids coupling Spring's preload to user-reloadable code.While rails/rails#57269 closes the bug part of this from the Rails side, this still makes sense on it's own.