annotate mercurial/help/hgignore.5.txt @ 26375:3686fa2b8eee

windows: insert file positioning call between reads and writes

fopen() and fdopen() have a unique-to-Windows requirement that
transitions between read and write operations in files opened
in modes r+, w+, and a+ perform a file positioning call
(fsetpos, fseek, or rewind) in between. While the MSDN docs don't
say what will happen if this is not done, observations reveal
that Python raises an IOError with errno 0. Furthermore, I
/think/ this behavior isn't deterministic. But I can reproduce
it reliably with subsequent patches applied that open revlogs
in a+ mode and perform both reads and writes.

This patch introduces a proxy class for file handles opened
in r+, w+, and a+ mode on Windows. The class intercepts calls
and audits whether a file positioning function has been called
between read and write operations. If not, a dummy, no-op seek
to the current file position is performed. This appears to be
sufficient to "trick" Windows into allowing transitions between
read and writes without raising errors.

==========
 hgignore
==========

---------------------------------
syntax for Mercurial ignore files
---------------------------------

:Author:         Vadim Gelfer <[e-mail]>
:Organization:   Mercurial
:Manual section: 5
:Manual group:   Mercurial Manual

.. include:: hgignore.5.gendoc.txt

Author
======
Vadim Gelfer <[e-mail]>

Mercurial was written by Matt Mackall <[e-mail]>.

See Also
========
|hg(1)|_, |hgrc(5)|_

Copying
=======
This manual page is copyright 2006 Vadim Gelfer.
Mercurial is copyright 2005-2015 Matt Mackall.
Free use of this software is granted under the terms of the GNU General
Public License version 2 or any later version.

.. include:: common.txt