mmap\'s resize method resizes the file in win32 but not unix

[myerscarpenter]

BPO	728515
Nosy	@loewis, @birkenfeld, @birkenfeld, @facundobatista, @josiahcarlson
Files	mmap-resize-diff

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/birkenfeld'
closed_at = <Date 2005-08-24.07:19:13.000>
created_at = <Date 2003-04-27.17:44:53.000>
labels = ['extension-modules']
title = "mmap\\'s resize method resizes the file in win32 but not unix"
updated_at = <Date 2005-08-24.07:19:13.000>
user = 'https://bugs.python.org/myerscarpenter'

bugs.python.org fields:

activity = <Date 2005-08-24.07:19:13.000>
actor = 'georg.brandl'
assignee = 'georg.brandl'
closed = True
closed_date = None
closer = None
components = ['Extension Modules']
creation = <Date 2003-04-27.17:44:53.000>
creator = 'myers_carpenter'
dependencies = []
files = ['862']
hgrepos = []
issue_num = 728515
keywords = []
message_count = 9.0
messages = ['15710', '15711', '15712', '15713', '15714', '15715', '15716', '15717', '15718']
nosy_count = 6.0
nosy_names = ['loewis', 'georg.brandl', 'georg.brandl', 'facundobatista', 'josiahcarlson', 'myers_carpenter']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue728515'
versions = ['Python 2.4']

[myerscarpenter]

In the resize method under win32 you have something
like this:

/* Move to the desired EOF position \*/
    SetFilePointer (self-\>file_handle,
            new_size, NULL, FILE_BEGIN);
    /* Change the size of the file \*/
    SetEndOfFile (self-\>file_handle);

Which resizes the file

Under Unix you need to call

   ftruncate(self->fileno, new_size)

before calling remap() to make it do the same thing.

[loewis]

Logged In: YES
user_id=21627

Would you like to contribute a patch? Please make sure to
include changes to the documentation and test suite.

[facundobatista]

Logged In: YES
user_id=752496

Please, could you verify if this problem persists in Python 2.3.4
or 2.4?

If yes, in which version? Can you provide a test case?

If the problem is solved, from which version?

Note that if you fail to answer in one month, I'll close this bug
as "Won't fix".

Thank you!

. Facundo

[facundobatista]

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user_id=752496

Deprecated. Reopen only if still happens in 2.3 or newer.

. Facundo

[josiahcarlson]

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user_id=341410

The problem still persists in Python 2.3 and 2.4. A quick
read of mmapmodule.c shows that ftruncate() is not being
called within the non-windows portion of mmap_resize_method().

[facundobatista]

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user_id=752496

Reopened as posted that still is a bug.

[birkenfeld]

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user_id=1188172

This is not trivial since the filehandle can be closed at
the time the ftruncate() would be necessary.

The Windows specific code duplicates the filehandle upon
mmap creation, perhaps the UNIX code should do this too?
Then, the ftruncate call can be inserted.

[birkenfeld]

Logged In: YES
user_id=1188172

Attaching patch which duplicates the file handle under UNIX
too (btw, the size() method was broken too), mimics Windows
behaviour with resize(), adds a testcase for this and
clarifies the docs.

[birkenfeld]

Logged In: YES
user_id=1188172

Okay, committed as
Modules/mmapmodule.c; 2.50; 2.48.4.1
Lib/test/test_mmap.py; 1.33; 1.30.18.1
Doc/lib/libmmap.tex; 1.12; 1.9.4.2