Process.detach cause sinatra-1.4.7 auto exit - ruby

Question

here is my code:
class App < Sinatra::Base
get "/" do
pid =fork do
end
Process.detach(pid)
end
end
App.start!
when i curl localhost:4567, the server auto exit and the output is:
127.0.0.1 - - [13/Aug/2016:23:45:18 CST] "GET / HTTP/1.1" 200 0
- -> /
[2016-08-13 23:45:18] INFO WEBrick::HTTPServer#start done.
== Sinatra has ended his set (crowd applauds)
my environment is:
Linux Mint 17.3 Rosa
ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-linux]
Why does Sinatra quit after just one request? I want it to keep running until I deliberately kill it.

Answer 1

It's not Process.detach that causes Sinatra to quit, but the fact that the forked process ends and runs its at_exit hooks, which shut down the server (though I'm not quite sure how that can leak from the child process to the parent).
There's a couple of simple ways to prevent this.
I prefer this set-and-forget solution:
configure do
disable :traps
end
The downside is that Ctrl-C causes a not-so-graceful exit.
Alternatively, add this to the beginning of any fork block:
settings.running_server = nil
The downside is that you need to remember to add this to all forked code.
You might also find someone suggesting at_exit { Process.exit! } in all fork blocks, but I think it's less reliable because other at_exit handlers could interfere with it.
Unfortunately, I don't see any configuration option in Sinatra that would fix forking and still allow graceful handling of Ctrl-C.