I've a process (Test::Builder, if you must know), which sends data to both STDERR and STDOUT. However, I need to read both and here are the requirements:

1. This must be a non-blocking read.
2. The streams must be read in synch.
3. It must be cross-platform.
4. It must run on the oldest version of Perl 5 possible.
5. It must be pure Perl.

Number 2 seems to require that I use a construct like `$someprocess 2>&1`, but that blocks and I don't know if it's portable. I do know that open FH, "$someprocess 2>&1 |" is blowing up on Windows with a 'bad file descriptor' error.

As far as I can tell, the only way to reliably solve this problem is some way of telling the source process to send everything to the same filehandle. Is there some other way of handling this without changing the source process?

Update: And I cannot use any non-core modules. There's a hope, however faint, that this work might eventually make it's way into the core, hence this and some of the above requirements.