RuntimeError - can't add a new key into hash during iteration

[bronson]

Got this backtrace in development mode while using my app... The page crashed instead of rendering. Haven't managed to reproduce it though. Tried a few times, both with and without clearing the cache first.

RuntimeError - can't add a new key into hash during iteration:
  /Users/bronson/.rubies/ruby-2.2.2/lib/ruby/2.2.0/set.rb:151:in `replace'
  /Users/bronson/.rubies/ruby-2.2.2/lib/ruby/2.2.0/set.rb:347:in `collect!'
  sprockets (3.5.2) lib/sprockets/loader.rb:85:in `asset_from_cache'
  sprockets (3.5.2) lib/sprockets/loader.rb:57:in `block in load'
  sprockets (3.5.2) lib/sprockets/loader.rb:312:in `block in fetch_asset_from_dependency_cache'
  sprockets (3.5.2) lib/sprockets/loader.rb:308:in `fetch_asset_from_dependency_cache'
  sprockets (3.5.2) lib/sprockets/loader.rb:44:in `load'
  sprockets (3.5.2) lib/sprockets/cached_environment.rb:20:in `block in initialize'
  sprockets (3.5.2) lib/sprockets/cached_environment.rb:47:in `load'
  sprockets (3.5.2) lib/sprockets/base.rb:66:in `find_asset'
  sprockets (3.5.2) lib/sprockets/base.rb:92:in `[]'
  sprockets-rails (3.0.1) lib/sprockets/rails/helper.rb:342:in `find_asset'
  sprockets-rails (3.0.1) lib/sprockets/rails/helper.rb:323:in `digest_path'
  sprockets-rails (3.0.1) lib/sprockets/rails/helper.rb:312:in `asset_path'
  sprockets-rails (3.0.1) lib/sprockets/rails/helper.rb:90:in `block in resolve_asset_path'
  sprockets-rails (3.0.1) lib/sprockets/rails/helper.rb:230:in `block in resolve_asset'
  sprockets-rails (3.0.1) lib/sprockets/rails/helper.rb:229:in `resolve_asset'
  sprockets-rails (3.0.1) lib/sprockets/rails/helper.rb:89:in `resolve_asset_path'
  sprockets-rails (3.0.1) lib/sprockets/rails/helper.rb:79:in `compute_asset_path'
  actionview (5.0.0.beta2) lib/action_view/helpers/asset_url_helper.rb:144:in `asset_path'
  actionview (5.0.0.beta2) lib/action_view/helpers/asset_url_helper.rb:281:in `stylesheet_path'
  sprockets-rails (3.0.1) lib/sprockets/rails/helper.rb:161:in `block (2 levels) in stylesheet_link_tag'
  sprockets-rails (3.0.1) lib/sprockets/rails/helper.rb:160:in `block in stylesheet_link_tag'
  sprockets-rails (3.0.1) lib/sprockets/rails/helper.rb:157:in `stylesheet_link_tag'
  app/views/layouts/print.html.haml:9:in `_app_views_layouts_print_html_haml__1453697812607104007_70324318851660'
  actionview (5.0.0.beta2) lib/action_view/template.rb:159:in `block in render'
  activesupport (5.0.0.beta2) lib/active_support/notifications.rb:166:in `instrument'
  actionview (5.0.0.beta2) lib/action_view/template.rb:353:in `instrument'
  actionview (5.0.0.beta2) lib/action_view/template.rb:157:in `render'
  actionview (5.0.0.beta2) lib/action_view/renderer/template_renderer.rb:66:in `render_with_layout'
  actionview (5.0.0.beta2) lib/action_view/renderer/template_renderer.rb:52:in `render_template'
  actionview (5.0.0.beta2) lib/action_view/renderer/template_renderer.rb:14:in `render'
  actionview (5.0.0.beta2) lib/action_view/renderer/renderer.rb:42:in `render_template'
  actionview (5.0.0.beta2) lib/action_view/renderer/renderer.rb:23:in `render'
  actionview (5.0.0.beta2) lib/action_view/rendering.rb:103:in `_render_template'
  actionpack (5.0.0.beta2) lib/action_controller/metal/streaming.rb:217:in `_render_template'
  actionview (5.0.0.beta2) lib/action_view/rendering.rb:83:in `render_to_body'
  actionpack (5.0.0.beta2) lib/action_controller/metal/rendering.rb:52:in `render_to_body'
  actionpack (5.0.0.beta2) lib/action_controller/metal/renderers.rb:144:in `render_to_body'
  actionpack (5.0.0.beta2) lib/abstract_controller/rendering.rb:25:in `render'
  actionpack (5.0.0.beta2) lib/action_controller/metal/rendering.rb:36:in `render'
  actionpack (5.0.0.beta2) lib/action_controller/metal/instrumentation.rb:43:in `block (2 levels) in render'
  activesupport (5.0.0.beta2) lib/active_support/core_ext/benchmark.rb:12:in `block in ms'
  /Users/bronson/.rubies/ruby-2.2.2/lib/ruby/2.2.0/benchmark.rb:303:in `realtime'
  activesupport (5.0.0.beta2) lib/active_support/core_ext/benchmark.rb:12:in `ms'
  actionpack (5.0.0.beta2) lib/action_controller/metal/instrumentation.rb:43:in `block in render'
  actionpack (5.0.0.beta2) lib/action_controller/metal/instrumentation.rb:86:in `cleanup_view_runtime'
  activerecord (5.0.0.beta2) lib/active_record/railties/controller_runtime.rb:25:in `cleanup_view_runtime'
  actionpack (5.0.0.beta2) lib/action_controller/metal/instrumentation.rb:42:in `render'
  app/controllers/comparisons_controller.rb:13:in `print'
  actionpack (5.0.0.beta2) lib/action_controller/metal/basic_implicit_render.rb:4:in `send_action'
  actionpack (5.0.0.beta2) lib/abstract_controller/base.rb:183:in `process_action'
  actionpack (5.0.0.beta2) lib/action_controller/metal/rendering.rb:30:in `process_action'
  actionpack (5.0.0.beta2) lib/abstract_controller/callbacks.rb:20:in `block in process_action'
  activesupport (5.0.0.beta2) lib/active_support/callbacks.rb:126:in `call'
  activesupport (5.0.0.beta2) lib/active_support/callbacks.rb:506:in `block (2 levels) in compile'
  activesupport (5.0.0.beta2) lib/active_support/callbacks.rb:455:in `call'
  activesupport (5.0.0.beta2) lib/active_support/callbacks.rb:101:in `__run_callbacks__'
  activesupport (5.0.0.beta2) lib/active_support/callbacks.rb:750:in `_run_process_action_callbacks'
  activesupport (5.0.0.beta2) lib/active_support/callbacks.rb:90:in `run_callbacks'
  actionpack (5.0.0.beta2) lib/abstract_controller/callbacks.rb:19:in `process_action'
  actionpack (5.0.0.beta2) lib/action_controller/metal/rescue.rb:27:in `process_action'
  actionpack (5.0.0.beta2) lib/action_controller/metal/instrumentation.rb:31:in `block in process_action'
  activesupport (5.0.0.beta2) lib/active_support/notifications.rb:164:in `block in instrument'
  activesupport (5.0.0.beta2) lib/active_support/notifications/instrumenter.rb:21:in `instrument'
  activesupport (5.0.0.beta2) lib/active_support/notifications.rb:164:in `instrument'
  actionpack (5.0.0.beta2) lib/action_controller/metal/instrumentation.rb:29:in `process_action'
  actionpack (5.0.0.beta2) lib/action_controller/metal/params_wrapper.rb:248:in `process_action'
  activerecord (5.0.0.beta2) lib/active_record/railties/controller_runtime.rb:18:in `process_action'
  actionpack (5.0.0.beta2) lib/abstract_controller/base.rb:128:in `process'
  actionview (5.0.0.beta2) lib/action_view/rendering.rb:30:in `process'
  actionpack (5.0.0.beta2) lib/action_controller/metal.rb:193:in `dispatch'
  actionpack (5.0.0.beta2) lib/action_controller/metal.rb:265:in `dispatch'
  actionpack (5.0.0.beta2) lib/action_dispatch/routing/route_set.rb:50:in `dispatch'
  actionpack (5.0.0.beta2) lib/action_dispatch/routing/route_set.rb:32:in `serve'
  actionpack (5.0.0.beta2) lib/action_dispatch/journey/router.rb:42:in `block in serve'
  actionpack (5.0.0.beta2) lib/action_dispatch/journey/router.rb:29:in `serve'
  actionpack (5.0.0.beta2) lib/action_dispatch/routing/route_set.rb:724:in `call'
  actionview (5.0.0.beta2) lib/action_view/digestor.rb:14:in `call'
  rack (2.0.0.alpha) lib/rack/etag.rb:25:in `call'
  rack (2.0.0.alpha) lib/rack/conditional_get.rb:25:in `call'
  rack (2.0.0.alpha) lib/rack/head.rb:12:in `call'
  actionpack (5.0.0.beta2) lib/action_dispatch/middleware/cookies.rb:608:in `call'
  activerecord (5.0.0.beta2) lib/active_record/query_cache.rb:36:in `call'
  activerecord (5.0.0.beta2) lib/active_record/connection_adapters/abstract/connection_pool.rb:963:in `call'
  activerecord (5.0.0.beta2) lib/active_record/migration.rb:558:in `call'
  actionpack (5.0.0.beta2) lib/action_dispatch/middleware/callbacks.rb:29:in `block in call'
  activesupport (5.0.0.beta2) lib/active_support/callbacks.rb:97:in `__run_callbacks__'
  activesupport (5.0.0.beta2) lib/active_support/callbacks.rb:750:in `_run_call_callbacks'
  activesupport (5.0.0.beta2) lib/active_support/callbacks.rb:90:in `run_callbacks'
  actionpack (5.0.0.beta2) lib/action_dispatch/middleware/callbacks.rb:27:in `call'
  actionpack (5.0.0.beta2) lib/action_dispatch/middleware/reloader.rb:71:in `call'
  actionpack (5.0.0.beta2) lib/action_dispatch/middleware/remote_ip.rb:79:in `call'
  better_errors (2.1.1) lib/better_errors/middleware.rb:84:in `protected_app_call'
  better_errors (2.1.1) lib/better_errors/middleware.rb:79:in `better_errors_call'
  better_errors (2.1.1) lib/better_errors/middleware.rb:57:in `call'
  actionpack (5.0.0.beta2) lib/action_dispatch/middleware/debug_exceptions.rb:49:in `call'
  actionpack (5.0.0.beta2) lib/action_dispatch/middleware/show_exceptions.rb:31:in `call'
  railties (5.0.0.beta2) lib/rails/rack/logger.rb:36:in `call_app'
  railties (5.0.0.beta2) lib/rails/rack/logger.rb:24:in `block in call'
  activesupport (5.0.0.beta2) lib/active_support/tagged_logging.rb:70:in `block in tagged'
  activesupport (5.0.0.beta2) lib/active_support/tagged_logging.rb:26:in `tagged'
  activesupport (5.0.0.beta2) lib/active_support/tagged_logging.rb:70:in `tagged'
  railties (5.0.0.beta2) lib/rails/rack/logger.rb:24:in `call'
  actionpack (5.0.0.beta2) lib/action_dispatch/middleware/request_id.rb:24:in `call'
  rack (2.0.0.alpha) lib/rack/method_override.rb:22:in `call'
  rack (2.0.0.alpha) lib/rack/runtime.rb:22:in `call'
  activesupport (5.0.0.beta2) lib/active_support/cache/strategy/local_cache_middleware.rb:28:in `call'
  actionpack (5.0.0.beta2) lib/action_dispatch/middleware/load_interlock.rb:13:in `call'
  actionpack (5.0.0.beta2) lib/action_dispatch/middleware/static.rb:136:in `call'
  rack (2.0.0.alpha) lib/rack/sendfile.rb:111:in `call'
  railties (5.0.0.beta2) lib/rails/engine.rb:522:in `call'
  rack (2.0.0.alpha) lib/rack/handler/webrick.rb:86:in `service'
  /Users/bronson/.rubies/ruby-2.2.2/lib/ruby/2.2.0/webrick/httpserver.rb:138:in `service'
  /Users/bronson/.rubies/ruby-2.2.2/lib/ruby/2.2.0/webrick/httpserver.rb:94:in `run'
  /Users/bronson/.rubies/ruby-2.2.2/lib/ruby/2.2.0/webrick/server.rb:294:in `block in start_thread'

[cllns]

I'm seeing this occasionally too. Looks like #518 could fix it :)

[dazzaroonie]

I too have just received this in the same way as @Karthik-Y

[Shelvak]

I have the same issue locally (dev) and in production, the problem is mainly a concurrency problem (i think) because I saw that only when a particular action is hitted a lot.

Issue: ActionView::Template::Error: can't add a new key into hash during iteration Line: <%= stylesheet_link_tag 'application', media: 'all' %> Ruby: ruby 2.4.1p111 Rails: 5.1.6 sprockets: 3.7.2 sprockets-rails: 3.2.1

Fixed with the Patch SprocketCache

I can test and notice the difference with $ ab -n 100 -c 10 URL

Cheers

[starrychloe]

I ran into this just now. I have not changed the assets. Rails 5.2.2, Ruby 2.5.3. I was just editing a text box with CKEditor gem and had uploaded an image file and when I saved, I got this error. I see git sees new files under public/ckeditor_assets/. I reloaded the page and it went away.

    public/ckeditor_assets/pictures/1/content_137506881909824295852507266618340761448.jpg
    public/ckeditor_assets/pictures/1/original_137506881909824295852507266618340761448.jpg
    public/ckeditor_assets/pictures/1/thumb_137506881909824295852507266618340761448.jpg

Completed 500 Internal Server Error in 5824ms (ActiveRecord: 291.6ms)

ActionView::Template::Error (can't add a new key into hash during iteration):
     6:   <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.2/css/bootstrap.min.css" integrity="sha384-Smlep5jCw/wG7hdkwQ/Z5nLIefveQRIY9nfy6xoR1uRYBtpZgI6339F5dgvm/e9B" cros
sorigin="anonymous">
     7:   <%= stylesheet_link_tag 'application', media: 'all', 'data-turbolinks-track' => true %>
     8:   <%= stylesheet_link_tag 'https://fonts.googleapis.com/css?family=Cabin:600|Open+Sans' %>
     9:   <%= javascript_include_tag 'application', 'data-turbolinks-track' => true %>
    10:   <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js" integrity="sha384-ZMP7rVo3mIykV+2+9J3UJ46jBk0WLaUAdn689aCwoqbBJiSnjAK/l8WvCWPIPm49" crossorigin="anonym
ous"></script>
    11:   <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.1.2/js/bootstrap.min.js" integrity="sha384-o+RDsa0aLu++PJvFqy8fFScvbHFLtbvScb8AjopnFD+iEQ7wo/CG0xlczd+2O/em" crossorigin="anonymous
"></script>
    12:   <script src="https://js.stripe.com/v3/"></script>

app/views/layouts/application.html.erb:9:in `_app_views_layouts_application_html_erb__135861518_81740640'

Here is a solution: http://stackoverflow.com/questions/25198085/ddg#27643890

[feliperaul]

Still seeing this at random on Rails 5.2.1, Ruby 2.5.3; refreshing the page works.

[AndreFSilveira]

+1 ActionView::Template::Error: can't add a new key into hash during iteration https://app.honeybadger.io/fault/57486/c6617f5edcae8560e3c2e8ccebaf5c5a

[mrsweaters]

I'm experiencing the same issue in ActionMailer when the view is rendered.

[nishankbhati]

I am experiencing same issue. Ruby 2.7.1 and rails-6. Occurs when traffic increases. Reproduced it using load-testing (i.e made bundle of 5 api calls) and ran it with 50 users on app hosted on EC-2 instance.

[kvokka]

Same issue with rails 6.1.rc1 & Ruby 2.5.8

Also got similar problem from ActiveRecord, https://github.com/rails/rails/issues/40608

[mohideen]

I experienced the same error while running my rails application in development mode on docker. In my case, increasing the memory under Docker preferences solved it for me (I was running a bunch of containers, and obviously 2GB was not sufficient. I increased it to 6GB).

[brandondrew]

I'm having this occur while load-testing a new server while we move from Ubuntu & NGINX on AWS to RedHat & Apache on VMware(?) VMs on internally hosted hardware.

We never had this happen on the old servers. (It's a brand-new error in Rollbar.) But now it happens less than 1% of the time (0.36% in my latest sample) during load testing. I have no idea which of the new variables to be suspicious of:

Ubuntu → RedHat NGINX → Apache AWS EC2 → VMware

But if anyone notices a pattern in your own experiences, please pipe up.

[hidr0]

We are experiencing the same thing in dev:

rails -> rails-7.0.4.2 sprockets -> sprockets-3.7.2 ruby -> ruby-2.7.8

What we did was run rails with puma with with 1 thread for now

max_threads_count = ENV.fetch("RAILS_MAX_THREADS") { 1 }
min_threads_count = ENV.fetch("RAILS_MIN_THREADS") { 1 }
threads min_threads_count, max_threads_count