Streaming using ActionController::Live resets current tenant to the default one

[Looooong]

Description

Whenever data are streamed by writing to response buffer from ActionController::Live, the Apartment::Tenant.current is reset back to the default tenant.

Reproduction

Sample project. The project is setup with 2 tenants:

• development is the default tenant.
• test is always used when accessing the site (refer to config/initializers/apartment.rb:102)

Reproduction steps:

• Run server in local (example: rails s).
• Go to path /stream (example: http://localhost:3000/stream).

Expected result

• Every lines should be test.
• Apartment::Tenant.current keeps its current value.

Actual behaviour

• The first few lines show test tenant (first 11 lines on my machine).
• The rest shows the default development tenant.

System configuration

Sample project. Refer to app/controllers/streams_controller.rb

• Database: Postgresql 9, SQLite3

• Apartment version: 2.2.0

• Rails (or ActiveRecord) version: 4.2.10, 5.2.3

• Ruby version: 2.3.3

[lcjury]

Each thread as his own connection and ActionController::Live execute actions on different threads.

What I think is happening here, is that you have 2 threads, the one who handles your connection does the switch (and the other is not), some actions of ActionController:Live are executed on the "other thread" who hasn't switched to your test tenant.

from the docs

The final caveat is that your actions are executed in a separate thread than the main thread. Make sure your actions are thread safe, and this shouldn't be a problem (don't share state across threads, etc).

~You're trying to share state across threads.~ (EDIT: mi assumption is wrong)

[Looooong]

I can understand that the entire action is executed in a child thread. Moreover, the main thread's locals is copied to the child thread. However, I don't get why current tenant is switched in the middle of the action after a call to response.stream.write.

If I modify the action like this, it works as expected:

  def show
    response.headers['Content-Type'] = 'text/event-stream'
    render plain: Array.new(PRINT_TIMES) { Apartment::Tenant.current }.join("\n")
  ensure
    response.stream.close
  end

[mikecmpbll]

certainly sounds like a threading issue. i don't know enough about how ActionController::Live works unfortunately, without spending a lot of time on this.

[Looooong]

I probably agree with you, this might be a threading issue. I think I will avoid ActionController::Live then.