[PATCH] util: simplify pipefilter and avoid subprocess race

[Martin Geisler]

Greg Ward <greg-hg at gerg.ca> writes:

> On Wed, May 6, 2009 at 6:23 PM, Martin Geisler <mg at daimi.au.dk> wrote:
>> # HG changeset patch
>> # User Martin Geisler <mg at lazybytes.net>
>> # Date 1241648562 -7200
>> # Node ID ea3ec68a61808013de543ea306da939c7146287e
>> # Parent  b0ce2595777bddf8d4a62119e3a2dfb8ca0078b4
>> util: simplify pipefilter and avoid subprocess race
>>
>> The subprocess module is not thread safe. Spawning a thread to read
>> the output leads to exceptions like this when Mercurial exits:
> [...]
>> +    p = subprocess.Popen(cmd, shell=True, close_fds=closefds,
>> +                         stdin=subprocess.PIPE, stdout=subprocess.PIPE)
>> +    pout, perr = p.communicate(s)
>> +    return pout
>
> But who wait()s on the subprocess?

In this case the communicate method does -- the documentation says:

  Interact with process: Send data to stdin. Read data from stdout and
  stderr, until end-of-file is reached. *Wait for process to terminate.*
  The optional input argument should be a string to be sent to the
  child process, or None, if no data should be sent to the child.

So I think we're okay here.

-- 
Martin Geisler

VIFF (Virtual Ideal Functionality Framework) brings easy and efficient
SMPC (Secure Multiparty Computation) to Python. See: http://viff.dk/.