[Qt-interest] [1/2 OT] ImageMagick, OpenMP and QThread [Mac OS X] [WORKAROUND]?

[Oliver.Knoll at comit.ch]

Knoll Oliver, ITS-CMT-SUI-SL-SFR-FIN-DEV wrote on Wednesday, January 27, 2010 4:38 PM:

> ...
> My application crashes when I want to create an ImageMagick "Image"
> within a QThread. This is the offending code: 

To whom it might concern, here is a crude workaround for the situation when you want to

- call ImageMagick (or any other library) from within a QThread (or any other thread such as POSIX)
- the compiler/OpenMP support library fails when called from a thread
  (see http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42616)

The workaround: disable OpenMP in ImageMagick. When you compile ImageMagick yourself, fine, simply add '--disable-openmp' when calling configure:

$> configure --disable-openmp

In my case I installed ImageMagick via "Mac Ports". I tried disabling some "port variants", like

$> sudo port install -v ImageMagick -- -openmp

but to no avail (I simply guessed the 'openmp' name), ImageMagick was always build with OpenMP support.


So I modified the 'Portfile'

1. Make sure you have write-access to
    /opt/local/var/macports/sources/rsync.macports.org/release/ports/graphics/Portfile

   (As administrator, I temporarily changed the owner of the graphics folder and Portfile
    from root to administrator, my admin user)

2. Append to section 'configure.args' the line --disable-openmp:

configure.args \
    --enable-shared \
    --enable-static \
    --disable-ltdl-install \
    [...]
    --without-rsvg \
    --without-lqr \
    --disable-openmp

3. Uninstall ImageMagick

$> sudo port uninstall ImageMagick

4. Install again

$> sudo port install -v ImageMagick

5. While the package is installing make sure that OpenMP support is really disabled, check CXXFLAGS (they are printed out when specifying the -v verbose option) etc. there should be no -fopenmp or -lgomp anymore:

  PREFIX          = /opt/local
  EXEC-PREFIX     = /opt/local
  VERSION         = 6.5.8
  CC              = /usr/bin/gcc-4.2 -std=gnu99
  CFLAGS          = -O2 -arch x86_64 -Wall -W -D_THREAD_SAFE
  CPPFLAGS        = -I/opt/local/include/ImageMagick
  PCFLAGS         = 
  DEFS            = -DHAVE_CONFIG_H
  LDFLAGS         = -L/opt/local/lib -L/opt/local/lib -L/opt/local/lib
  MAGICK_LDFLAGS  = -L/opt/local/lib -L/opt/local/lib -L/opt/local/lib -L/opt/local/lib
  LIBS            = -lMagickCore -ltiff -lfreetype -ljpeg -L/opt/local/lib -lfontconfig -lexpat -lfreetype -lz -liconv -lXext -lSM -lICE -lX11 -lXt -lbz2 -lz -lm -lpthread -lltdl
  CXX             = /usr/bin/g++-4.2
  CXXFLAGS        = -O2 -arch x86_64 -Wall -W -D_THREAD_SAFE


When I uninstalled the ImageMagick package the 'Portfile' still remained at its place. But I don't know when it is updated, maybe with an 'port upgrade' command at some time. And obviously you have to install ImageMagick a first time to actually have this file ;)


Hope this is of any help to anyone :)

Cheers, Oliver
-- 
Oliver Knoll
Dipl. Informatik-Ing. ETH
COMIT AG - ++41 79 520 95 22