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Re: creating size-limited tar files

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Ian Kelly <ian.g.kelly@gmail.com> writes:

> On Tue, Nov 13, 2012 at 3:31 AM, andrea crotti
> <andrea.crotti.0@gmail.com> wrote:
>> but it's a bit ugly.  I wonder if I can use the subprocess PIPEs to do
>> the same thing, is it going to be as fast and work in the same way??
>
> It'll look something like this:
>
>>>> p1 = subprocess.Popen(cmd1, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>>>> p2 = subprocess.Popen(cmd2, shell=True, stdin=p1.stdout, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>>>> p1.communicate()
> ('', '')
>>>> p2.communicate()
> ('', '')
>>>> p1.wait()
> 0
>>>> p2.wait()
> 0
>
> Note that there's a subtle potential for deadlock here.  During the
> p1.communicate() call, if the p2 output buffer fills up, then it will
> stop accepting input from p1 until p2.communicate() can be called, and
> then if that buffer also fills up, p1 will hang.  Additionally, if p2
> needs to wait on the parent process for some reason, then you end up
> effectively serializing the two processes.
>
> Solution would be to poll all the open-ended pipes in a select() loop
> instead of using communicate(), or perhaps make the two communicate
> calls simultaneously in separate threads.

Or, you could just change the p1's stderr to an io.BytesIO instance.
Then call p2.communicate *first*.

-- 
regards,
kushal

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Thread

creating size-limited tar files andrea crotti <andrea.crotti.0@gmail.com> - 2012-11-07 17:13 +0000
  Re: creating size-limited tar files Neil Cerutti <neilc@norwich.edu> - 2012-11-07 18:40 +0000
  Re: creating size-limited tar files Alexander Blinne <news@blinne.net> - 2012-11-07 20:05 +0100
    Re: creating size-limited tar files Roy Smith <roy@panix.com> - 2012-11-07 15:32 -0500
      Re: creating size-limited tar files Andrea Crotti <andrea.crotti.0@gmail.com> - 2012-11-07 21:52 +0000
      Re: creating size-limited tar files Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-11-07 23:15 +0000
      Re: creating size-limited tar files andrea crotti <andrea.crotti.0@gmail.com> - 2012-11-08 10:11 +0000
      Re: creating size-limited tar files andrea crotti <andrea.crotti.0@gmail.com> - 2012-11-08 10:29 +0000
      Re: creating size-limited tar files andrea crotti <andrea.crotti.0@gmail.com> - 2012-11-09 10:39 +0000
      Re: creating size-limited tar files andrea crotti <andrea.crotti.0@gmail.com> - 2012-11-13 10:31 +0000
      Re: creating size-limited tar files Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-13 09:07 -0700
      Re: creating size-limited tar files Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-13 09:25 -0700
      Re: creating size-limited tar files Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-13 09:30 -0700
      Re: creating size-limited tar files Kushal Kumaran <kushal.kumaran+python@gmail.com> - 2012-11-14 11:35 +0530
      Re: creating size-limited tar files Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-14 00:22 -0700
      Re: creating size-limited tar files Kushal Kumaran <kushal.kumaran+python@gmail.com> - 2012-11-14 14:21 +0530
      Re: creating size-limited tar files andrea crotti <andrea.crotti.0@gmail.com> - 2012-11-14 11:52 +0000
      Re: creating size-limited tar files andrea crotti <andrea.crotti.0@gmail.com> - 2012-11-14 15:56 +0000
      Re: creating size-limited tar files Dave Angel <d@davea.name> - 2012-11-14 11:10 -0500
      Re: creating size-limited tar files andrea crotti <andrea.crotti.0@gmail.com> - 2012-11-14 16:16 +0000
  Re: creating size-limited tar files Dave Angel <d@davea.name> - 2012-11-14 11:33 -0500
  Re: creating size-limited tar files Andrea Crotti <andrea.crotti.0@gmail.com> - 2012-11-14 20:43 +0000
  Re: creating size-limited tar files Dave Angel <d@davea.name> - 2012-11-14 15:57 -0500

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