sample code of Sinatra integration does not work with classic style application

[okazu-dm]

I found sample code of Sinatra integration does not work if application is classic style.

I mean This sample code has a problem.
Sinatra classic style application start in at_exit
https://github.com/sinatra/sinatra/blob/2b5d1b45097f67c06a2345f0d8c30db2b38030bf/lib/sinatra/main.rb#L45
and Datadog::Writer.stop_worker method is called in at_exit
https://github.com/DataDog/dd-trace-rb/blob/v0.54.2/lib/ddtrace/writer.rb#L97

So current sample code means following execution order

1. Datadog::Writer.stop_worker is executed
2. Sinatra::Application.run!

(at_exit handlers are executed in reverser order of registration https://ruby-doc.org/core-3.1.1/Kernel.html#method-i-at_exit)

https://gist.github.com/okazu-dm/480f6188d2be7573b07c364cfac14194

[delner]

Thanks for the report!

I haven't dug into Sinatra's internals yet. Do you know why this at_exit hook exists in Sinatra code? I can see how the order issue causes problems, but it's not clear why 1) Sinatra is using this to start(?) an application and 2) why at_exit is triggered at all while starting up an application.

It's also surprising to me that this slipped through our unit tests. Something worth looking at why.

[TonyCTHsu]

👋 @okazu-dm , have you resolved this issue? Recently, we have introduced a bunch of improvement at 1.6.0 for Sinatra, give it a try and tell us about it 😉