[Patches] [ python-Patches-1407135 ] anonymous mmap

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Patches item #1407135, was opened at 2006-01-16 09:44
Message generated for change (Comment added) made by titty
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Category: Library (Lib)
Group: Python 2.4
Status: Open
Resolution: None
Priority: 5
Submitted By: Ralf Schmitt (titty)
Assigned to: Nobody/Anonymous (nobody)
Summary: anonymous mmap

Initial Comment:
make mmap.mmap(-1, size) map anonymous memory on both windows 
and unix-like systems.

If this goes in, I'll also write some documentation.

here's some more reasoning:
https://sourceforge.net/tracker/?
func=detail&atid=105470&aid=1402308&group_id=5470


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>Comment By: Ralf Schmitt (titty)
Date: 2006-01-18 10:16

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Thanks for the insight.
And yes, I forgot to check that little box.

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Comment By: Neal Norwitz (nnorwitz)
Date: 2006-01-18 07:24

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To answer your question:  
> Aren't the tests being run before release on all major
platforms?

It's difficult to answer.  I think generally the answer is
yes, but it all depends on volunteers.  We are currently
running tests on every checkin: 
http://www.python.org/dev/buildbot/ for both HEAD and 2.4
branch.  BuildBot is a relatively recent addition though. 
On OS X 10.3, we aren't having a problem with mmap(). 
Various developers I know use OS X, not sure which versions
of OS X though.

--
General comments about the patch:  For any solution, we
should strive to make it available if possible (with reason)
on all platforms.  We should attempt to have all versions of
Python behave similarly.  (I'm not trying to imply you
aren't working in this direction, it seems like you are.)

I only notice one patch attached.  Have you been deleting
the others or did you forget to check the litle box?


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Comment By: Ralf Schmitt (titty)
Date: 2006-01-17 11:34

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This patch tries to mmap via /dev/zero if neither MAP_ANON
nor MAP_ANONYMOUS is defined and handles the case where only
MAP_ANONYMOUS is defined.

I've added some tests, and found that test_mmap executed
mmap(-1, ...), which probably would have crashed the tests
running on OS X. Aren't the tests being run before release
on all major platforms?


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Comment By: Ralf Schmitt (titty)
Date: 2006-01-17 09:59

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Well, seems like one would also need some special handling for 
systems only defining one of MAP_ANON/MAP_ANONYOUS:

http://www.winehq.org/hypermail/wine-devel/2004/12/0064.html


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Comment By: Ralf Schmitt (titty)
Date: 2006-01-17 09:48

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quoting ubuntu's mmap man page:

MAP_ANONYMOUS
  The mapping is not backed by any file; the fd and  offset
 arguments  are ignored.  This flag in conjunction with
MAP_SHARED is implemented since Linux 2.4.

MAP_ANON
  Alias for MAP_ANONYMOUS. Deprecated.

---

On a glibc 2.1 system (once installed with a 2.2 kernel, now
running a 2.4 one) the manpage doesn't even mention
MAP_ANON(YMOUS).
The patch in it's current form will just fail on system's
not defining MAP_ANON (i.e. mmap will fail and an exception
will be raised).

However, according to Stevens 'Advanced Programming in the
Unix Environment', chapter 14.9, there are two ways to mmap
anonymous memory.
The first one works by using MAP_ANON (4.3+BSD),
and the second one works by opening /dev/zero and passing
that as a filedescriptor to mmap (SVR4).

So, I guess all BSD's and newer Linux Systems would work
with this version. Anyway I can send another patch handling
that case if you like?


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Comment By: Neal Norwitz (nnorwitz)
Date: 2006-01-17 06:22

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In addition to docs, tests will also be necessary before
committing.

What if fd == -1 and MAP_ANON is not defined?  It seems the
state could be inconsistent.  Shouldn't an exception be
raised in this case?

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