From: Charles Oliver Nutter <headius@...>
Date: 2009-08-03T22:06:51+09:00
Subject: Re: JRuby, ffi, bad file descriptor

Ahhh. Yeah I see the problem.

In JRuby, because we don't normally have access to the "real" file
descriptor for any IO channel, all our logic for fileno is basically
fake. We keep an artificial list of numbers that map to IO channels
and use that as our file descriptor table. In this case, you're
pulling in a real file descriptor from the system, which does not
exist in our table, so we raise an error.

In order for us to support arbitrary descriptors in our IO we'd
probably need an implementation of IO that used all low-level C APIs
rather than Java IO APIs. There's currently no (public) way to get
from a file descriptor to an IO channel in Java APIs.

So I'll divert this issue by asking: what does this get you that our
built-in tempfile support does not? We do not use MRI's tempfile.rb;
we've implemented our own on top of Java's tempfile support that
performs quite a bit better. Perhaps there's a missing feature we can
add.

It would also be worth discussing this with Wayne Meissner. It would
certainly be *nice* if we could transparently support real file
descriptors, and he may know a way to do it.

On Mon, Aug 3, 2009 at 7:21 AM, Daniel Berger<djberg96@gmail.com> wrote:
> On Aug 2, 10:34 pm, Charles Oliver Nutter <head...@headius.com> wrote:
>> Got the source of that temp.rb handy? It looks like it's passing a
>> bad/closed descriptor to IO.new or something...
>
> require 'ffi'
>
> class FileTemp < File
>   extend FFI::Library
>
>   attach_function 'fileno',  [:pointer], :int
>   attach_function 'fclose',  [:pointer], :int
>   attach_function 'mkstemp', [:string],  :int
>   attach_function 'tmpfile', [],         :pointer
>   attach_function 'tmpnam',  [:string],  :string
>   attach_function 'umask',   [:int],     :int
>
>   TMPDIR = ENV['TEMP'] || ENV['TMP'] || '/tmp'
>
>   def initialize(delete = true, template = 'rb_file_temp_XXXXXX')
>      @fptr = nil
>
>      if delete
>         @fptr = tmpfile()
>         fd = fileno(@fptr)
>      else
>         begin
>            omask = umask(077)
>            fd = mkstemp(template)
>            raise SystemCallError, 'mkstemp()' if fd < 0
>         ensure
>            umask(omask)
>         end
>      end
>
>      super(fd, 'wb+')
>   end
>
>   def close
>      super
>      fclose(@fptr) if @fptr
>   end
>
>   def self.temp_name
>      TMPDIR + tmpnam(nil) << '.tmp'
>   end
> end
>
> if $0 == __FILE__
>   fh = FileTemp.new
>   fh.print 'hello'
>   fh.close
> end
>
>