Do not inline process mailers when calling deliver_all_later #55659

chaadow · 2025-09-11T19:41:22Z

Motivation / Background

This Pull Request has been created to fix #55658

Detail

In our application we store each email attempt/delivery inside a table for tracking purposes, and I was surprised that deliver_all_later was taking a lot of time to send around 2000 emails. after looking at the logs i figured that all mailers were processed as if i was calling deliver_now

Additional information

@fatkodima I still don't know why by looking at this caller stack, but it seems flatten! eager load the mails by trying to delegate a method which triggers the inline processing here:

rails/actionmailer/lib/action_mailer/message_delivery.rb

Lines 65 to 67 in aedfc4a

    
           def __getobj__ # :nodoc: 
        
             @mail_message ||= processed_mailer.message 
        
           end

Here is the `callers` output

``` "/Users/user/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/gems/sentry-rails-5.26.0/lib/sentry/rails/tracing.rb:56:in 'Sentry::Rails::Tracing::SentryNotificationExtension#instrument'", "/Users/user/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/bundler/gems/rails-d18731bed119/activesupport/lib/active_support/notifications.rb:210:in 'ActiveSupport::Notifications.instrument'", "/Users/user/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/bundler/gems/rails-d18731bed119/actionmailer/lib/action_mailer/base.rb:651:in 'ActionMailer::Base#process'", "/Users/user/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/bundler/gems/rails-d18731bed119/actionmailer/lib/action_mailer/message_delivery.rb:170:in 'block in ActionMailer::MessageDelivery#processed_mailer'", ":91:in 'Kernel#tap'", "/Users/user/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/bundler/gems/rails-d18731bed119/actionmailer/lib/action_mailer/message_delivery.rb:169:in 'ActionMailer::MessageDelivery#processed_mailer'", "/Users/user/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/bundler/gems/rails-d18731bed119/actionmailer/lib/action_mailer/message_delivery.rb:66:in 'ActionMailer::MessageDelivery#__getobj__'", "/Users/user/.rbenv/versions/3.4.5/lib/ruby/3.4.0/delegate.rb:101:in 'Delegator#respond_to_missing?'", "/Users/user/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/bundler/gems/rails-d18731bed119/actionmailer/lib/action_mailer/message_delivery.rb:23:in 'respond_to?'", "/Users/user/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/bundler/gems/rails-d18731bed119/actionmailer/lib/action_mailer/message_delivery.rb:23:in 'Array#flatten!'", "/Users/user/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/bundler/gems/rails-d18731bed119/actionmailer/lib/action_mailer/message_delivery.rb:23:in 'ActionMailer._deliver_all_later'", "/Users/user/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/bundler/gems/rails-d18731bed119/actionmailer/lib/action_mailer/message_delivery.rb:10:in 'ActionMailer.deliver_all_later'",


</details>
I can't figure out how this line is called `"/Users/user/.rbenv/versions/3.4.5/lib/ruby/gems/3.4.0/bundler/gems/rails-d18731bed119/actionmailer/lib/action_mailer/message_delivery.rb:23:in 'respond_to?'"`
when calling `flatten!` at line 23, it tries to call `respond_to?`
### Checklist
Before submitting the PR make sure the following are checked:
* [x] This Pull Request is related to one change. Unrelated changes should be opened in separate PRs.
* [x] Commit message has a detailed description of what changed and why. If this PR fixes a related issue include it in the commit message. Ex: `[Fix #issue-number]`
* [x] Tests are added or updated if you fix a bug or add a feature.
* [ ] CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature. Minor bug fixes and documentation changes should not be included.

chaadow · 2025-09-11T20:20:22Z

actionmailer/lib/action_mailer/message_delivery.rb


    private
      def _deliver_all_later(delivery_method, *deliveries, **options)
-        deliveries.flatten!


after some research, i think what happens is the following:

flatten! tries to call respond_to? on each element

respond_to? gets delegated to __getobj__

which calls @mail_message ||= processed_mailer.message

and processed_mailer triggers the inline processing of the mailer

correct, flatten! calls Array() which calls respond_to?(:to_ary) and so on

chaadow · 2025-09-11T20:34:32Z

actionmailer/test/message_delivery_test.rb

+
+    assert_not mail1.processed?
+    assert_not mail2.processed?
+  end


thanks for merging @fatkodima . But sorry if you don't mind i'm going to add back at least the test where we pass an array to properly test if deliveries.first.is_a?(Array)

rails-bot bot added the actionmailer label Sep 11, 2025

chaadow force-pushed the fix_deliver_all_later_inline_processing branch from 17cb5ca to a6dea41 Compare September 11, 2025 19:43

Do not inline process mailers when calling deliver_all_later

c9926bc

fatkodima force-pushed the fix_deliver_all_later_inline_processing branch from a6dea41 to c9926bc Compare September 11, 2025 20:05

fatkodima merged commit 864227e into rails:main Sep 11, 2025
2 of 3 checks passed

chaadow commented Sep 11, 2025

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chaadow mentioned this pull request Sep 11, 2025

Add missing test when an array is passed to ActionMailer.deliver_all_later #55660

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chaadow commented Sep 11, 2025

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Do not inline process mailers when calling deliver_all_later #55659

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chaadow commented Sep 11, 2025 •

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	def __getobj__ # :nodoc:
	@mail_message \|\|= processed_mailer.message
	end

Do not inline process mailers when calling deliver_all_later #55659

Do not inline process mailers when calling deliver_all_later #55659

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chaadow commented Sep 11, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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chaadow commented Sep 11, 2025 •

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