#<FiberError: fiber called across threads>

[ianeinser]

Hi there,

we got this errors when trying to run multiple engine drivers in upstream.rb. It seems that the method Thread.new doesnt play nicely with Eventmachine Symphony which is based on Fiber.

this is the full error.

#<Thread:0x000055a3665aa410@/home/app/app/workers/daemons/upstream.rb:8 run> terminated with exception (report_on_exception is true):
(eval):8:in resume': fiber called across threads (FiberError) from (eval):8:in block in get'
from /opt/vendor/bundle/ruby/2.6.0/gems/eventmachine-1.2.7/lib/em/deferrable.rb:151:in set_deferred_status' from /opt/vendor/bundle/ruby/2.6.0/gems/eventmachine-1.2.7/lib/em/deferrable.rb:191:in succeed'
from /opt/vendor/bundle/ruby/2.6.0/gems/em-http-request-1.1.7/lib/em-http/client.rb:113:in unbind' from /opt/vendor/bundle/ruby/2.6.0/gems/em-http-request-1.1.7/lib/em-http/client.rb:71:in on_request_complete'
from /opt/vendor/bundle/ruby/2.6.0/gems/em-http-request-1.1.7/lib/em-http/http_connection.rb:204:in block in post_init' from /opt/vendor/bundle/ruby/2.6.0/gems/em-http-request-1.1.7/lib/em-http/http_connection.rb:219:in <<'
from /opt/vendor/bundle/ruby/2.6.0/gems/em-http-request-1.1.7/lib/em-http/http_connection.rb:219:in receive_data' from /opt/vendor/bundle/ruby/2.6.0/gems/em-http-request-1.1.7/lib/em-http/http_connection.rb:26:in receive_data'
from /opt/vendor/bundle/ruby/2.6.0/gems/eventmachine-1.2.7/lib/eventmachine.rb:195:in run_machine' from /opt/vendor/bundle/ruby/2.6.0/gems/eventmachine-1.2.7/lib/eventmachine.rb:195:in run'
from /opt/vendor/bundle/ruby/2.6.0/gems/em-synchrony-1.0.6/lib/em-synchrony.rb:39:in synchrony' from /home/app/app/workers/daemons/upstream.rb:12:in process'
from /home/app/app/workers/daemons/upstream.rb:8:in block (3 levels) in run' {"level":"ERROR","time":"2021-05-10 03:31:41","message":"#<FiberError: fiber called across threads>"} {"level":"ERROR","time":"2021-05-10 03:31:41","message":"(eval):8:in resume'\n(eval):8:in block in get'\n/opt/vendor/bundle/ruby/2.6.0/gems/eventmachine-1.2.7/lib/em/deferrable.rb:151:in set_deferred_status'\n/opt/vendor/bundle/ruby/2.6.0/gems/eventmachine-1.2.7/lib/em/deferrable.rb:191:in succeed'\n/opt/vendor/bundle/ruby/2.6.0/gems/em-http-request-1.1.7/lib/em-http/client.rb:113:in unbind'\n/opt/vendor/bundle/ruby/2.6.0/gems/em-http-request-1.1.7/lib/em-http/client.rb:71:in on_request_complete'\n/opt/vendor/bundle/ruby/2.6.0/gems/em-http-request-1.1.7/lib/em-http/http_connection.rb:204:in block in post_init'\n/opt/vendor/bundle/ruby/2.6.0/gems/em-http-request-1.1.7/lib/em-http/http_connection.rb:219:in <<'\n/opt/vendor/bundle/ruby/2.6.0/gems/em-http-request-1.1.7/lib/em-http/http_connection.rb:219:in receive_data'\n/opt/vendor/bundle/ruby/2.6.0/gems/em-http-request-1.1.7/lib/em-http/http_connection.rb:26:in receive_data'\n/opt/vendor/bundle/ruby/2.6.0/gems/eventmachine-1.2.7/lib/eventmachine.rb:195:in run_machine'\n/opt/vendor/bundle/ruby/2.6.0/gems/eventmachine-1.2.7/lib/eventmachine.rb:195:in run'\n/opt/vendor/bundle/ruby/2.6.0/gems/em-synchrony-1.0.6/lib/em-synchrony.rb:39:in synchrony'\n/home/app/app/workers/daemons/upstream.rb:12:in process'\n/home/app/app/workers/daemons/upstream.rb:8:in block (3 levels) in run'"}

It seems that Fiber and Thread do not play well with each other. Hence we replace Thread.new with Fiber.new but upstream can only read one engine driver and ignore the rest. Feedback and suggestions are appreciated.

openware original code:
Engine.all.map { |e| Thread.new { process(e) } }.map(&:join)

we change to:
Engine.all.map { |e| Fiber.new { process(e) } }.map(&:join)

Thank you