No live threads left. Deadlock?

[JakeTheSnake3p0]

Expected behavior

Rails view should generate asset links without issue.

Actual behavior

The view is never generated and the browser ends up waiting for a response that never comes. Logs do not help. I only found out about the cause of the problem when running my rspec tests for simple GET requests to pages I know were working before upgrading sprockets.

Failure/Error: <%= stylesheet_link_tag :application, media: :all %>

     fatal:
       No live threads left. Deadlock?
       5 threads, 5 sleeps current:0x0000000c708aa0 main thread:0x000000018485d0
       * #<Thread:0x0000000187b7b0 sleep_forever>
          rb_thread_t:0x000000018485d0 native:0x007f24dbf7e700 int:0
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/concurrent-ruby-1.0.5/lib/concurrent/synchronization/mri_lockable_object.rb:43:in `sleep'
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/concurrent-ruby-1.0.5/lib/concurrent/synchronization/mri_lockable_object.rb:43:in `wait'
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/concurrent-ruby-1.0.5/lib/concurrent/synchronization/mri_lockable_object.rb:43:in `ns_wait'
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/concurrent-ruby-1.0.5/lib/concurrent/synchronization/abstract_lockable_object.rb:43:in `ns_wait_until'
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/concurrent-ruby-1.0.5/lib/concurrent/atomic/event.rb:87:in `block in wait'
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/concurrent-ruby-1.0.5/lib/concurrent/synchronization/mri_lockable_object.rb:38:in `block in synchronize'
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/concurrent-ruby-1.0.5/lib/concurrent/synchronization/mri_lockable_object.rb:38:in `synchronize'
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/concurrent-ruby-1.0.5/lib/concurrent/synchronization/mri_lockable_object.rb:38:in `synchronize'
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/concurrent-ruby-1.0.5/lib/concurrent/atomic/event.rb:84:in `wait'
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/concurrent-ruby-1.0.5/lib/concurrent/concern/obligation.rb:75:in `wait'
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/concurrent-ruby-1.0.5/lib/concurrent/concern/obligation.rb:87:in `wait!'
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/sprockets-4.0.0.beta5/lib/sprockets/manifest.rb:130:in `each'
          /home/ubuntu/.rvm/gems/ruby-2.4.0@sprucewood/gems/sprockets-4.0.0.beta5/lib/sprockets/manifest.rb:130:in `find'

System configuration

• Sprockets version 4.0.0.beta5 onward
• Ruby version 2.4.0
• Vagrant on Windows 7 x64 running Ubuntu with vagrant-winnfsd

Example App

I suppose any basic app would do, I tested beta6, beta5 and finally beta4 before the problem went away.

[wjordan]

The fact this occurs in 4.0.0.beta5 onward makes me think this is possibly related to #469, which was merged in that version and changed some concurrency behavior. If you could provide a minimal verifiable example that reproduces this issue I can take a detailed look. Otherwise it might be harder to track down the issue but I'll see if I can reproduce any similar issue on my own.

In the meantime, setting environment.export_concurrent = false (config.assets.export_concurrent = false in Rails I think?) will disable concurrent processing as a possible workaround.