[pypy-dev] Dead loop occurs when using python-daemon and multiprocessing together in PyPy 4.0.1

[Vincent Legoll]

Do you thought about that removed code ?
https://bitbucket.org/vincentlegoll/pypy/commits/992e29624c5fd8a7e76677acf085fea0520f576d

The filedesc was not kept opened there, or do you meant another thing
in this file ?

On Wed, Dec 23, 2015 at 6:24 PM, Armin Rigo <arigo at tunes.org> wrote:
> Hi Maciej,
>
> On Wed, Dec 23, 2015 at 3:48 PM, Maciej Fijalkowski <fijall at gmail.com>
> wrote:
>>
>> I bet the difference is due to "we see more FDs in pypy". If you close the
>> correct FD in CPython, it would break too I presume? Or is there special
>> code to handle that?
>
>
> There is special code to handle that in CPython.  It is actually very
> carefully checking that the FD is still open *and* still pointing to what it
> used to.  See Python/random.c.
>
> Just thinking aloud: what could occur here is that the forked process
> reopens an unrelated file at this descriptor, and then our os.urandom()
> tries to read from it---and, as a guess, the file happens to be a socket
> opened in non-blocking mode, and our implementation of os.urandom() gets 0
> bytes and keeps trying to get more, which throws it into an infinite loop.
>
> It seems it would be a good idea to copy the careful behavior of CPython.
> (There used to be another case of file descriptor kept open internally, in
> rpython/rtyper/lltypesystem/llarena.py for /dev/zero, but this is gone.)
>
>
> A bientôt,
>
> Armin.
>
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-- 
Vincent Legoll