In article <[EMAIL PROTECTED]>, "Gabriel Genellina" <[EMAIL PROTECTED]> wrote:
> En Thu, 01 Mar 2007 14:42:00 -0300, <[EMAIL PROTECTED]> escribió: > > > BUT If I use PIPE for both (so I can .write() on the stdin and .read() > > from the subprocess' stdout stream (better: file descriptor)) reading > > from the subprocess stdout blocks forever. If I write something onto > > the subprocess' stdin that causes it to somehow proceed, I can read > > from its stdout. > > On http://docs.python.org/lib/popen2-flow-control.html there are some > notes on possible flow control problems you may encounter. It's a nice summary of one problem, a deadlock due to full pipe buffer when reading from two pipes. The proposed simple solution depends too much on the cooperation of the child process to be very interesting, though. The good news is that there is a real solution and it isn't terribly complex, you just have to use select() and UNIX file descriptor I/O. The bad news is that while this is a real problem, it isn't the one commonly encountered by first time users of popen. The more common problem, where you're trying to have a dialogue over pipes with a program that wasn't written specifically to support that, is not solvable per se - I mean, you have to use another device (pty) or redesign the application. > If you have no control over the child process, it may be safer to use a > different thread for reading its output. Right - `I used threads to solve my problem, and now I have two problems.' It can work for some variations on this problem, but not the majority of them. Donn Cave, [EMAIL PROTECTED]
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