From: Eric Hodel <drbrain@...7.net>
Date: 2004-04-27T08:48:25-07:00
Subject: Re: ignores SIGPIPE, why ruby

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Zsban Ambrus (ambrus@math.bme.hu) wrote:

> Ruby ignores SIGPIPE.  In this mail, I'll argue against the usefulness of
> this decision.

No, Ruby does not ignore SIGPIPE.  It traps it just fine.

> When you type something like
>=20
> ruby -we 'n=3D 1; puts n+=3D1 while 1;' | head
>=20
> then after the 10th line the puts function raises Errno::EPIPE (cause tha=
t's
> what syscalls return when they raise an EPIPE signal) and ruby dies with =
an
> ugly annoying message like
>=20
> -e:1:in `write': Broken pipe (Errno::EPIPE)
>         from -e:1:in `puts'
>         from -e:1
>=20
> I think that ruby should either silently die from the EPIPE signal (or el=
se
> raise an Errno::EPIPE exception that you can catch but if you don't catch=
 it
> ruby should just exit silently just like when you call Kernel.exit())

Ruby did not recive a SIGPIPE, puts raised an Errno::EPIPE.  See
errno(2) vs signal(3).

You can close or redirect STDERR to avoid the error message.

> What makes the situation even worse is that when I try to change tshi
> behaiviour like this:
>=20
> ruby -we 'trap "PIPE" do exit end; n=3D 1; puts n+=3D1 while 1;' | head
>=20
> the trap function does not do anything, it does not catch the SIGPIPE. The
> trap function should at least raise an error because it does not catch the
> signal.

That code never recieves a SIGPIPE signal, it raises an Errno::EPIPE.
trap "PIPE" works just fine:

$ cat x.rb
pid =3D fork do
  trap 'PIPE' do puts "caught SIGPIPE"; exit end
  File.open '/dev/null', 'a' do |fp|
    loop do fp.puts end
  end
end

sleep 1
Process.kill 'PIPE', pid
$ ruby x.rb
caught SIGPIPE


> The only way to silence the error message is to wrap the whole script
> in a begin .... rescue Errno::EPIPE; end;

def main
  # ...
rescue Errno::EPIPE
  exit
end

main if $0 =3D=3D __FILE__

> If ruby would just leave the signal as is, you could probabyl still
> have the old behaiviour by adding a trap for SIGPIPE that raises an
> Errno::EPIPE exception, or just by ignoring the signal and supposing
> that the syscall that raised SIGPIPE will get an EPIPE error anyway
> thus raise the exception.

No signal sent.

--=20
Eric Hodel - drbrain@segment7.net - http://segment7.net
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