aeris/rails-deadlock

Rails strange deadlock

This project is damn small and standard, but got a deadlock when accessing / route.

Just start the server (rails s) and try to access / (http http://localhost:3000). It will just hang forever, no way to stop the server anymore (ctrl-c not working, only kill -9 works) The culprit line is app/controllers/application_controller.rb#7

app/models/instance_base.rb

module InstanceBase
end

app/controllers/application_controller.rb

class ApplicationController < ActionController::Base
    def index
        pool = Concurrent::FixedThreadPool.new 1
        1.times do
            pool.post do
                p InstanceBase # Hang here
            end
        end
        pool.shutdown
        pool.wait_for_termination
        head :ok
    end
end

If commenting the thread pool (lines 5 & 7), it works… Same thread pooled code works directly on a script (see bin/crashtest.rb)

Seems the trouble is on the rails class loader, forcing preload of InstanceBase outside the thread pool restore a good behavior.