I recently implemented this in psutil and thought it would have been a nice addition for subprocess module as well:
https://code.google.com/p/psutil/issues/detail?id=440

Patch in attachment introduces a new subprocess.wait_procs() utility function which waits for multiple processes (Popen instances) to terminate.
The use case this covers is quote common: send SIGTERM to a list of processes, wait for them to terminate, send SIGKILL as last resort:


>>> def on_terminate(proc):
...     print("process {} terminated".format(proc))
...
>>> for p in procs:
...    p.terminate()
...
>>> gone, still_alive = wait_procs(procs, timeout=3, callback=on_terminate)
>>> for p in still_alive:
...     p.kill()


Are we still in time for Python 3.4?

It's not, the beta is already out.

I do not think this is ready to live in the standard library.  

I've left some comments on your patch review.  Consider those for incorporation into the psutils project.

wait_procs() implementation should live in the psutils module on PyPI with more iteration on its implementation happening there as it isn't ready yet.

In general: We have too many APIs in the subprocess module.  I want to avoid adding more unless they are a very clear improvement to ease of use of the module.  More things with deadlock caveats similar to the existing Popen.wait() call are undesirable.

I replied to your comments here:
http://bugs.python.org/review/19843/
Assuming the deadlock problem gets fixed would you consider this feature worthy for inclusion?

I'd rather see it bake in psutils for a while longer regardless of implementation.