python subprocess with timeout and large output (>64K)

I want to execute a process, limit the execution-time by some timeout in seconds and grab the output produced by the process. And I want to do this on windows, linux and freebsd.

I have tried implementing this in three different ways:

1. cmd - Without timeout and subprocess.PIPE for output capture.

   BEHAVIOUR: Operates as expected but does not support timeout, i need timeout...

2. cmd_to - With timeout and subprocess.PIPE for output capture.

   BEHAVIOUR: Blocks subprocess execution when output >= 2^16 bytes.

3. cmd_totf - With timeout and tempfile.NamedTemporaryfile for output capture.

   BEHAVIOUR: Operates as expected but uses temporary files on disk.

These are available below for closer inspection.

As can be seen in the output below, then the timeout-code blocks the execution of the sub-process when using subprocessing.PIPE and output from the subprocess is >= 2^16 bytes.

The subprocess documentation states that this is expected when calling process.wait() and using subprocessing.PIPE, however no warnings are given when using process.poll(), so what is going wrong here?

I have a solution in cmd_totf which use the tempfile module but the tradeoff is that it writes the output to disk, something I would REALLY like to avoid.

So my questions are:

• What am I doing wrong in cmd_to?
• Is there a way to do what I want and without using tempfiles / keeping the output in memory.

Script to generate a bunch of output ('exp_gen.py'):

#!/usr/bin/env python
import sys
output  = "b"*int(sys.argv[1])
print output

Three different implementations (cmd, cmd_to, cmd_totf) of wrappers around subprocessing.Popen:

#!/usr/bin/env python
import subprocess, time, tempfile
bufsize = -1

def cmd(cmdline, timeout=60):
  """
  Execute cmdline.
  Uses subprocessing and subprocess.PIPE.
  """