ImageMagick and OpenMP (was Re: Adding configure options when installing a port)

[Stephen Langer]

On Jun 17, 2010, at 3:34 PM, Stephen Langer wrote:

> 
> On Jun 17, 2010, at 3:17 PM, Scott Webster wrote:
> 
>> On Thu, Jun 17, 2010 at 12:08 PM, Ryan Schmidt <ryandesign at macports.org> wrote:
>>> 
>>> On Jun 17, 2010, at 14:05, Scott Webster wrote:
>>>> I'm not entirely sure I agree with disabling by default.  Unless I was
>>>> reading this list, I would never have known about this issue, and
>>>> would just go with the default.  Disabling openmp would slow down
>>>> everything (well, not quite everything I guess) I do with ImageMagick
>>>> by a factor of 2.  Same would happen with other ports that can use
>>>> openmp if it was disabled there...
>>>> 
>>>> I guess I'm just saying that there is a trade-off between universal
>>>> compatibility and speed here.  I don't have a good handle on how big
>>>> of an issue the compatibility thing is.  If it's quite isolated then I
>>>> think having the twice (or more) as fast option as default is
>>>> reasonable.
>>> 
>>> Users are expected to read the output of "port variants" to decide if they might want to use any of those variants...
>>> 
>> 
>> Sure... but:
>> 
>> a) Lots of people probably don't do that, perhaps particularly for
>> "common" ports like ImageMagick, or if it is installed as a
>> dependency.
>> 
>> b) Lots of people would not understand that they likely want openmp enabled.
>> 
>> c) Couldn't this apply almost as well to the people who want openmp
>> disabled too?  In Stephen's case his software is not distributed via
>> macports.  Is there software in macports that breaks with openmp
>> enabled here?  If so, it would be nice for macports to recognize this
>> and tell them to use the no-openmp variant, but #126 :(
>> 
>> Anyway, this is just the way I see it.
> 
> 
> I don't know if there are other packages in macports that would break.  I would like to be able to distribute our program from macports, but that's not going to happen soon.  In the meantime, telling our users to install the no-openmp variant of imagemagick would be ok with us.
> 
> I'll see if I can get the ImageMagick folks to comment on turning openmp on and off at runtime.

I asked about this issue on the ImageMagick board.  They seem to understand the problem, and aren't going to do anything about it until the OpenMP standard specifies how it should interact with threads.

 -- Steve

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