Re: [matplotlib-devel] binary installers for python2.6; libpng segfault, MSVCR90.DLL and mingw

[John H. <jd...@gm...>]

On Wed, Jun 10, 2009 at 4:41 PM, John Hunter<jd...@gm...> wrote:

> Drop the tar.gz into release/win32 and then following the instructions
> in release/win32/README.txt

I should add one more detail here.  distutils for python2.6 adds a
dependency to MSVCR90.DLL, and Charlie has a distutils hack in
release/win32/data/setupwin.py to try
and banish the msvcr90.dll which is not on most systems; he sets the
distutils dll_libraries to the empty list::


    from distutils import cygwinccompiler

    try:
            # Python 2.6
            # Replace the msvcr func to return an empty list
            cygwinccompiler.get_msvcr
            cygwinccompiler.get_msvcr = lambda: []

w/o this hack you will get a dll import error rather than a segfault.
You can toggle the hack on and off by changing in the Makefile::


  # on
  ${PYTHON} setupwin.py build_ext -c mingw32 -I ${PY_INCLUDE} -L
${PY_LINKER} bdist_wininst

  # off
  ${PYTHON} setup.py build_ext -c mingw32 -I ${PY_INCLUDE} -L
${PY_LINKER} bdist_wininst

The problem is that the dll cannot be found on the system and
apparently the right solution is to include it in a framework as
described by David in the link I posted

  http://cournape.wordpress.com/2008/09/02/how-to-embed-a-manifest-into-a-dll-with-mingw-tools-only/

but I think this is something of a red herring because w/ Charlie's
hack _png links against MSVCRT.DLL rather than MSVCR90.DLL but still
segfaults (only on python2.6) on the png_write_info call.  I also
tried forcing 'msvcr71' in the distutils hack which is what python2.5
usesbut to no avail.  When I said I wasted a lot of time chasing down
false leads, most of that was spent on trying various versions of mpl,
numpy, distutils, and the distutils MSVCR hacks, but in the end none
of it mattered.

But for the record I am including some notes I took while
experimenting with different things.  When I write below

  Interestingly, depwalker can find the DLL where PYTHON26.DLL depends
  on, pointing to C:\WINDOWS\WinSxS.VC90.CRT_1fgobbledygook on my box,
  but cannot find it where _PNG.PYD depends on it.

this was before I discovered David's essay on side-by-side assemblies
which explains why the linker finds python's MSVCR90.DLL  but not
_pngs.  What it doesn't explain is why w/ Charlie's hack, when we link
against MSVCRT.DLL or  MSVCR71.DLL, png is still segfaulting, and I
think the answer there is what I pointed to in my first post, the
broken time support in mingw MSVCR90.DLL.  Support for this is in my
note below::

  This time it finds it, but two of the functions are colored red
  indicating a problem: _fstati64 and gmtime.


Notes on the _png segfault and the MSVCR hacks
======================================

I have been working on the windows installers for mpl 98.5.3.  I am
able to build for python2.5 w/o problems, but when building for
python2.6, I get an DLL local error on any extension code


    cd matplotlib-0.98.5.3/build/lib.win32-2.6/matplotlib
    > /c/python26/python -c 'import _png'
    Traceback (most recent call last):
    File "<string>", line 1, in <module>
    ImportError: DLL load failed: The specified procedure could not be found.

when I open _PNG.PYD this file in dependency walker, I see a
dependency on MSVCR90.DLL which is flagged with a question mark "Error
opening file.  The system cannot find the file specified".  All the
*.PYD files have this dependency, including the numpy pyd files, but
most of them have it buried under a PYTHON26.DLL dependency, and
_PNG.PYD has it as a direct dependency (top level).  Interestingly,
depwalker can find the DLL where PYTHON26.DLL depends on, pointing to
C:\WINDOWS\WinSxS.VC90.CRT_1fgobbledygook on my box, but cannot find
it where _PNG.PYD depends on it.


When I look at _PNG.PYD for python2.5 (which is working fine and I've
uploaded the installers) I see a dependency for MSVCR71.DLL located in
C:/windows/system32, and the functions it provides include fclose,
fopen, putc, etc. which libpng apparently needs for file I/O.

As mentioned above, my system *does* have MSVCR90.DLL deep in
C:\WINDOWS\WinSxS.VC90.CRT_1fgobbledygook, and when I move it into
C:\windows\system32 and then reopen _png.pyd in depdendency walker, I
still get an error.  This time it finds it, but two of the functions
are colored red indicating a problem: _fstati64 and gmtime.

Charlie has a distutils hack in release/win32/data/setupwin.py.  Wen I
build the installer using the hacked distutils I can load the DLL file
in mpl either by importing matplotlib._png or in dependency walker.
In depwalker, the msvcrt90.DLL is replaced by MSVCRT.DLL at the top
level _PNG.PYD dependency, but the MSVCR90.DLL is still buried deep
under PYTHON26.DLL.  Unfortunately, use of this module triggers a
segfault.