Re: [boost] Half-baked GIL IO extension review

Subject: Re: [boost] Half-baked GIL IO extension review
From: Edd Dawson (lists_at_[hidden])
Date: 2010-12-08 14:12:22

Hi Christian,

On 12/7/2010 9:18 PM, Christian Henning wrote:

>>>> 2. is it wise to drag the stuff from e.g. the IJG JPEG library's public
>>>> headers in to client scope? I ask because I've had clashes with the
>>>> "boolean" macro before and this would outright prevent me from using the
>>>> library. The implication of addressing this would probably mean that the
>>>> GIL
>>>> would no longer be header-only. That's fine by me, but perhaps it's a
>>>> design
>>>> goal of the GIL for some reason?
>>>
>>> Would a namespace do the trick?
>>
>> In what way?
>>
>> (FWIW, after checking I now see "boolean" is a typedef rather than a macro,
>> but there was a clash nonetheless).
>
> I meant something like:
>
> namespace libjpeg {
>
> extern "C" {
> #include<jpeglib.h>
> }
>
> } // namespace libjpeg
>

Would this work if libjpeg was compiled with a C++ compiler? (though perhaps 
that won't be supported, in the end).

>>>> - What is your evaluation of the implementation?
>>>>
>>>> Looking again at the JPEG code here. As far as I can tell setjmp/longjmp
>>>> have been used with appropriate care, but I worry what will happen if a
>>>> method on a Device throws an exception, for example. I've had both Visual
>>>> C++ 2008 and Apple's g++ 4.0.1 crash on me in this kind of situation.
>>>
>>> Do you mean when an std::fstream throws an exception or when FILE
>>> issues an error?
>>
>> I was thinking of when a stream (or streambuf) of whatever kind throws an
>> exception.
>
> I think the user should catch the exception. io_new is also throwing
> exceptions when needed.

They might not have a chance when an exception is thrown from a function that is 
called from C (one of the callbacks installed in jpeg_decompress_struct, for 
example). All (portable) bets are off in this situation, as far as I know. This 
is where the boost::current_exception() suggestion comes from. You can catch and 
store the exception inside the callback (as best as possible) and then rethrow 
it when you're safely back in C++ land.

>>>> - What is your evaluation of the documentation?
>>>>
>>>> Couldn't find a lot. Either my eyes are poor, or the documentation is :)
>>>
>>> Did you see the .qbk file in the /doc folder?
>>
>> Gah, no. My eyes, then! I must have got lost in the deep folder hierarchy.
>
> ;-) I should have build the documentation before the review. It's my fault.

I forgot to say in my previous reply, but this now changes my vote as to whether 
the library should be included to a Yes.

Kind regards,

Edd