From: Tanaka Akira <akr@...>
Date: 2010-02-24T23:12:41+09:00
Subject: [ruby-core:28327] Re: [Bug:trunk] add explicit constraints for 	WONTFIX IO bug

2010/2/22 Yusuke ENDOH <mame@tsg.ne.jp>:
>
> In short, it means "IO#dup should not be used" and "IO that was once
> passed to IO#reopen should be just closed."
> "bezarre behavior" does not mean undefined behavior (such as SEGV),
> but means wrong order of reading and writing, wrong value from
> IO#pos, etc.  (see Appendix)
>
> These behaviors are caused by bug of core's wrong buffering handing.

I think it is difficult to fix.

The "bizarre" behavior can be occur without IO#dup and IO#reopen.

By IO.new:

% ./ruby -e '
f1 = File.new("foo.txt")
f2 = IO.new(f1.fileno)
p f1.gets
p f2.gets
'
"A\n"
nil

file descriptors may be shared at outside of ruby:

% ./ruby -e '
f1 = IO.new(3)
f2 = IO.new(4)
p f1.gets
p f2.gets
' 3< foo.txt 4<&3
"A\n"
nil

file descriptors may be shared between processes:

% ( ./ruby -e 'p STDIN.gets'; ./ruby -e 'p STDIN.gets' ) < foo.txt
"A\n"
nil

This behavior is inherent result of buffering.

I think we should live with this behavior because
buffering is important for performance.
-- 
Tanaka Akira