Arbitrary IO object

Hi,

How would I go about using IO.new such that it would automatically
grab the next available file descriptor? I don’t know the fileno in
advance and I can’t use StringIO.

What are my options?

Thanks,

Dan

On 20.05.2008 18:40, Daniel B. wrote:

How would I go about using IO.new such that it would automatically
grab the next available file descriptor?

Not sure what you mean: File.open uses a new file descriptor. Why would
you care about the file descriptor numbering?

I don’t know the fileno in
advance and I can’t use StringIO.

Why would you want to use StringIO to read from files?

What are my options?

What are you trying to achieve?

Kind regards

robert

On May 20, 11:25 am, Robert K. [email protected] wrote:

Why would you want to use StringIO to read from files?

What are my options?

What are you trying to achieve?

I’m tinkering with possibly reimplementing win32-open3 using the win32-
process library. You can redirect stdin, stdout and stderr like so:

info = Process.create(
input = IO.new(x, ‘w+’) # Want next available fd
output = IO.new(y, ‘w+’) # Want next available fd
error = IO.new(z, ‘w+’) # Want next available fd

:app_name => command,
:creation_flags => Process::DETACHED_PROCESS,
:startup_info => {
:stdin => input,
:stdout => output,
:stderr => error
}
)

pid = info.process_id

return [input, output, error, pid]

That’s the general idea, anyway.

Regards,

Dan

On May 20, 12:36 pm, Gary W. [email protected] wrote:

:creation_flags => Process::DETACHED_PROCESS,
mechanism in order to be useful via IO.new. You can
use IO#fileno to discover the underlying OS file
descriptor from a Ruby object but if you’ve already
got a Ruby IO object you don’t need to use IO.new.

At the C/POSIX level I don’t think there is really
any concept of specifying the ‘next available fd’.
You just call open/create/pipe/dup and use the integer
file descriptors that are returned. The OS figures
out which integer descriptors are available.

Yep, looks like I should just use IO.pipe.

Thanks,

Dan

On May 20, 2008, at 1:34 PM, Daniel B. wrote:

  :stdout => output,
  :stderr => error

}
)

IO.new is for associating a Ruby IO object with
an already open OS file descriptor. So you’ve got
to acquire the file descriptor through some non-Ruby
mechanism in order to be useful via IO.new. You can
use IO#fileno to discover the underlying OS file
descriptor from a Ruby object but if you’ve already
got a Ruby IO object you don’t need to use IO.new.

At the C/POSIX level I don’t think there is really
any concept of specifying the ‘next available fd’.
You just call open/create/pipe/dup and use the integer
file descriptors that are returned. The OS figures
out which integer descriptors are available.

Gary W.

On 20.05.2008 19:34, Daniel B. wrote:

advance and I can’t use StringIO.
output = IO.new(y, ‘w+’) # Want next available fd
error = IO.new(z, ‘w+’) # Want next available fd

It does not seem to make sense to open all these both for reading and
writing.

:app_name => command,
:creation_flags => Process::DETACHED_PROCESS,
:startup_info => {
:stdin => input,
:stdout => output,
:stderr => error
}
)

Not sure what this is supposed to do - this isn’t even valid Ruby as far
as I can see:

$ ruby -c <<EOF

info = Process.create(
input = IO.new(x, ‘w+’) # Want next available fd
output = IO.new(y, ‘w+’) # Want next available fd
error = IO.new(z, ‘w+’) # Want next available fd

:app_name => command,
:creation_flags => Process::DETACHED_PROCESS,
:startup_info => {
:stdin => input,
:stdout => output,
:stderr => error
}
)
EOF
-:3: syntax error, unexpected tIDENTIFIER, expecting ‘)’
output = IO.new(y, ‘w+’) # Want next available fd
^
-:6: syntax error, unexpected tASSOC, expecting $end
:app_name => command,
^

$

pid = info.process_id

return [input, output, error, pid]

That’s the general idea, anyway.

You only have two options:

  • you overlay a process, then it makes sense that the new process
    inherits all standard file descriptors (0,1,2 - stdin, stdout, stderr).
    Usually nothing needs to be done for this (at least on POSIX systems)

  • you copy the process (fork on POSIX) and want to be in control of the
    child’ IO, in that case you need to establish pipes to feed stdin and
    read from stdout and stderr.

Kind regards

robert

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