Feature #12693: Want a way to receive EINTR on Process.waitpid

• Status: Rejected
• Assignee: -
• Target version: -

[sonots (Naotoshi Seo)]

http://man7.org/linux/man-pages/man2/waitpid.2.html tells EINTR error if WNOHANG flag was not set and an unblocked signal or a SIGCHLD was caught.

However, ruby implementation of Process.waitpid does not raise EINTR https://github.com/ruby/ruby/blob/c2bf7e6f7d2fbe0b50da59aaa1374222f233aa71/process.c#L910-L911

test.rb

puts Process.pid

trap(:CONT) do
  puts 'CONT'
end

_pid = fork do
  sleep 10
end

Process.waitpid(-1)

$ ruby test.rb

$ kill -CONT xxxx # waitpid does not raise EINTR

I want a way or an option to get EINTR error on sending signal so that I can release blocking of waitpid.
It is same for wait, waitpid2, wait2, too.

[sonots (Naotoshi Seo)]

• Subject changed from Want to a way to receive EINTR on Process.waitpid to Want a way to receive EINTR on Process.waitpid

[shyouhei (Shyouhei Urabe)]

Naotoshi Seo wrote:

However, ruby implementation of Process.waitpid does not raise EINTR

No you don't. It is an extremely bad idea to use signal to interrupt execution.

Is it you must use signal for some reason or you just want to avoid infinite blocking? What if, for instance waitpid would take extra argument as timeout?

[sonots (Naotoshi Seo)]

I am currently using Timeout hack for when I wanted to get EINTR like https://github.com/sonots/ruby-server-starter/blob/7fbc8db2548c215aae02afef385caa683040bd8a/lib/server/starter.rb#L215-L223.

I was glad if I did not need to write such a hacky code.

[sonots (Naotoshi Seo)]

If adding an option to raise EINTR is not acceptable, adding timeout option is acceptable for my case.

[naruse (Yui NARUSE)]

You can raise exception on main threadh by Thread.main.raise in trap.

[sonots (Naotoshi Seo)]

It worked like a charm :)

test.rb

puts Process.pid

trap(:CONT) do
  raise 'CONT'
end

_pid = fork do
  sleep 10
end

begin
  Process.waitpid(-1)
rescue => e
  puts e.backtrace.join("\n")
end

Sending signal, I got

test.rb:4:in `block in <main>'
test.rb:12:in `waitpid'
test.rb:12:in `<main>'

[sonots (Naotoshi Seo)]

• Status changed from Open to Rejected