Puma sleeps an important thread on boot of rails application - ruby-on-rails

Question

I am running Rails 3 with Ruby 2.3.3 on puma with postgresql. I have an initializer/twitter.rb file that starts a thread on boot with a streaming api for twitter. When I use rails server to start my application, the twitter streaming works and I can reach my website like normal. (If I do not put the streaming on a different thread, the streaming works but I can not view my application in the browser since the thread is blocked by the twitter stream). But when I use puma -C config/puma.rb to start my application, I get the following message that is telling me that my thread was found on startup and was put to sleep. How can I tell puma to let me run this thread in the background on startup?
initializer/twitter.rb
### START TWITTER THREAD ### if production
if Rails.env.production?
puts 'Starting Twitter Stream...'
Thread.start {
twitter_stream.user do |object|
case object
when Twitter::Tweet
handle_tweet(object)
when Twitter::DirectMessage
handle_direct_message(object)
when Twitter::Streaming::Event
puts "Received Event: #{object.to_yaml}"
when Twitter::Streaming::FriendList
puts "Received FriendList: #{object.to_yaml}"
when Twitter::Streaming::DeletedTweet
puts "Deleted Tweet: #{object.to_yaml}"
when Twitter::Streaming::StallWarning
puts "Stall Warning: #{object.to_yaml}"
else
puts "It's something else: #{object.to_yaml}"
end
end
}
end
config/puma.rb
workers Integer(ENV['WEB_CONCURRENCY'] || 2)
threads_count = Integer(ENV['RAILS_MAX_THREADS'] || 5)
threads threads_count, threads_count
preload_app!
rackup DefaultRackup
port ENV['PORT'] || 3000
environment ENV['RACK_ENV'] || 'development'
on_worker_boot do
# Valid on Rails up to 4.1 the initializer method of setting `pool` size
ActiveSupport.on_load(:active_record) do
config = ActiveRecord::Base.configurations[Rails.env] ||
Rails.application.config.database_configuration[Rails.env]
config['pool'] = ENV['RAILS_MAX_THREADS'] || 5
ActiveRecord::Base.establish_connection(config)
end
end
Message on startup
2017-04-19T23:52:47.076636+00:00 app[web.1]: Connecting to database specified by DATABASE_URL
2017-04-19T23:52:47.115595+00:00 app[web.1]: Starting Twitter Stream...
2017-04-19T23:52:47.229203+00:00 app[web.1]: Received FriendList: --- !ruby/array:Twitter::Streaming::FriendList []
2017-04-19T23:52:47.865735+00:00 app[web.1]: [4] * Listening on tcp://0.0.0.0:13734
2017-04-19T23:52:47.865830+00:00 app[web.1]: [4] ! WARNING: Detected 1 Thread(s) started in app boot:
2017-04-19T23:52:47.865870+00:00 app[web.1]: [4] ! #<Thread:0x007f4df8bf6240#/app/config/initializers/twitter.rb:135 sleep> - /app/vendor/ruby-2.3.3/lib/ruby/2.3.0/openssl/buffering.rb:125:in `sysread'
2017-04-19T23:52:47.875056+00:00 app[web.1]: [4] - Worker 0 (pid: 7) booted, phase: 0
2017-04-19T23:52:47.865919+00:00 app[web.1]: [4] Use Ctrl-C to stop
2017-04-19T23:52:47.882759+00:00 app[web.1]: [4] - Worker 1 (pid: 11) booted, phase: 0
2017-04-19T23:52:48.148831+00:00 heroku[web.1]: State changed from starting to up
Thanks in advance for the help. I have looked at several other posts mentioning WARNING: Detected 1 Thread(s) started in app boot but the answers say to ignore the warning if the thread is not important. In my case, the thread is very important and I need this thread to not sleep.

Answer 1

From your code I think you have a bigger issue on your hands than a sleeping thread... which I guess might be caused by the fact that some things are misnamed and others are just not often considered when relying on a web framework.
In the world of servers, "workers" refer to forked processes that perform server related tasks, often accepting new connections and handling web requests.
BUT - fork doesn't duplicate threads! - the new process (the worker) starts with only one single thread, which is a copy of the thread that called fork.
This is because processes don't share memory (normally). Whatever global data you have in a process is private to that process (i.e., if you save connected websocket clients in an array, that array is different for each "worker").
This can't be helped, it's part of how the OS and fork are designed.
So, the warning is not something you can circumvent - it's an indication of a design flaw in the app(!).
For example, in your current design (assuming the thread wasn't sleeping), the handle_tweet method will only be called for the original server process and it won't be called for any worker process.
If you're using pub/sub, you only need one twitter_stream connection for the whole app (no matter how many servers or workers you application has) - perhaps a twitter_stream process (or background app) will be better than a thread.
But if you're implementing handle_tweet in a process specific way - i.e., by sending a message to every connected clients saved in an array - you need to make sure every "worker" initiates a twitter_stream thread(!).
When I wrote Iodine (a different server than Puma), I handled these use cases using the Iodine.run method, which defers tasks for later. The "saved" task should be performed only after the workers are initialized and the event loop starts running, so it's performed in each process (allowing you to start a new tread in each proccess).
i.e.
Iodine.run do
Thread.start do
twitter_stream.user do |object|
# ...
end
end
end
I assume Puma has a similar solution. From what I understand of the Puma Clustered-Mode Documentation, Adding the following block to your config/puma.rb might help:
# config/puma.rb
on_worker_boot do
Thread.start do
twitter_stream.user do |object|
# ...
end
end
end
Good luck!
EDIT: relating to the comment about twitter_stream using ActiveRecord
From the comments I gather that the twitter_stream callbacks store data in the DataBase as well as handle "push" events or notices.
Although these two concerns are connected, they are very different from each other.
For example, twitter_stream callbacks should only store data in the DataBase once. Even if your application grows to a billion users, you will only need to save the data in the database once.
This means that the twitter_stream callbacks should have their own dedicated process that runs only once, possibly separate from the main application.
At first, and as long as you limit your application to a single (only one server/application running), you might use fork together with the initializer/twitter.rb script... i.e.:
### START TWITTER PROCESS ### if production
if Rails.env.production?
puts 'Starting Twitter Stream...'
Process.fork do
twitter_stream.user do |object|
# ...
end
end
end
On the other hand, notifications should be addressed to a specific user on a specific connection owned by a specific process.
Hence, notifications should be a separate concern from the twitter_stream DataBase update and they should be running in the background of every process, using the on_worker_boot (or Iodine.run) described above.
To achieve this, you might have on_worker_boot start a background thread that will listen to a pub/sub service such as Redis, while the twitter_stream callbacks "publish" updates to the pub/sub service.
This would allow each process to review the update and check if any of the connections it "owns" belongs to a client that should be notified of the update.

Answer 2

The way I'm reading your question, this doesn't look like an issue. A sleeping thread is different from a dead thread. Sleep just means that the thread is waiting idle, not consuming any cpu. If all else is hooked up properly, then as soon as the twitter api detects an event, it should wake the the thread up, run whatever handler you've defined, and then go right back to sleep. Sleeping isn't "running in the background," but it is "waiting for something to happen (e.g. someone tweets #me.) so I can run in the background."
A quick example to demonstrate this:
2.4.0 :001 > t = Thread.new { TCPServer.new(1234).accept ; puts "Got a connection! Dying..." }
=> #<Thread:0x007fa3941fed90#(irb):1 sleep>
2.4.0 :002 > t
=> #<Thread:0x007fa3941fed90#(irb):1 sleep>
2.4.0 :003 > t
=> #<Thread:0x007fa3941fed90#(irb):1 sleep>
2.4.0 :004 > TCPSocket.new 'localhost', 1234
=> #<TCPSocket:fd 35>
2.4.0 :005 > Got a connection! Dying...
t
=> #<Thread:0x007fa3941fed90#(irb):1 dead>
Sleeping just means "waiting for action."
Puma is a thread-based server, and is very particular about spinning threads up in its boot process, hence the warning about a thread started at app boot.
For what it's worth though, it's kind of weird to have a thread listening for updates from an api like that in a webserver. Maybe you should look into having a worker handle twitter events using something like Resque? Or maybe ActionCable is relevant to your use case?