Redirecting stdout/err under win32 platform

[David Douard]

Hi everybody,

let me explain by problem:
I am working on an application which consists in a C++ dll (numeric
computations) and a Python IHM (Python/Tk), which must run under Linux and
win32. My problem is the C++ lib does write stuffs on its stdout, and I
would like to print those messages in a Tk frame. When I run the
computation, it has it's own thread.

So my question is : how van I redirect the dll's stdout to something I can
retrieve in Python (pipe, socket,...)?

I can do it easily under Linux. I made tests with a socket which just works
fine. In the threaded function (that will do the heavy computation), I
write:

import os, sys
from socket import *
s=socket(AF_UNIX, SOCK_STREAM)
s.connect(...)
os.dup2(sys.__stdout__.fileno(), s.fileno())
very_intensive_function(many_parameters)
s.close()

That's OK under Linux, but does not work under win32 (even if I use an INET
localhost socket), cause I cannot do the os.dup2 trick (Windows does not
want to consider a socket as a file! What a shity system!).

So my question is : is there a simple solution ? I have tested different
solutions. I am trying hacks with pipes created with the win32api. But I
have not yet managed this simple operation.

Note that I have no access to the dll source code, so I cannot modify it so
it uses a named pipe (for example) as message output pipe instead os
stdout...

Thanks,
David

 

[yaipa]

David,

Googling comp.lang.python /w this string "stderr win32" yielded 109
results.
So I think if you poke around a bit you will find your answer in the
archives.

Sorry for no direct help tonight...

Cheers,

--Alan

 

[David Douard]

Alan,

I did search Google for this problem (not enough, thou).
In fact, I found some kind of solution (by myself, not that much on Google),
but it is not really satisfactory.

I have used win32 pipes to do so (win32api.CreatePipe). I can redirect
stdout/stderr to it from my python code (even redirecting the stdout/stderr
from my C lib).
But I still have a problem with this solution (well, 2):
- it is *much* more complicated than any solution available on Unix like
systems (not really a problem, but),
- it not synchronous at all. And I'd like it to be so (or almost so).

David

 

[Pierre Barbier de Reuille]

David Douard a écrit :

Alan,

I did search Google for this problem (not enough, thou).
In fact, I found some kind of solution (by myself, not that much on Google),
but it is not really satisfactory.

I have used win32 pipes to do so (win32api.CreatePipe). I can redirect
stdout/stderr to it from my python code (even redirecting the stdout/stderr
from my C lib).
But I still have a problem with this solution (well, 2):
- it is *much* more complicated than any solution available on Unix like
systems (not really a problem, but),
- it not synchronous at all. And I'd like it to be so (or almost so).

David

AFAIK, there is no working bidirectionnal pipes on Windows ! The
functions exists in order for them to claim being POSIX, but they're not
working properly. Under Windows environment, I suppose you have to find
your way using their buggy pipes (and by no means their "POSIX" pipes)
or you have to use another inter-process communication protocol (DDE,
COM, ...).

Pierre

 

[David Bolen]

AFAIK, there is no working bidirectionnal pipes on Windows ! The
functions exists in order for them to claim being POSIX, but they're
not working properly. (...)

Can you clarify what you believe doesn't work properly? The os.popen*
functions under Windows use native CreateProcess calls to create the
child process and connect stdin/out/err handles to that child process,
so should behave properly. (Subject of course to the same risk of
deadlocks and what not due to buffering or queued up data that any
system would have with these calls)

-- David