[C++-sig] Am I crazy or is it my computer?

[Niall Douglas]

On 31 Oct 2007 at 15:11, Matthew Scouten wrote:

> Ok, I just found this:
> http://www.boost.org/libs/python/doc/v2/faq.html#threadsupport
> 
> I seems to be saying that I can not do what I want with out patching
> Boost::Python (or does this only apply to multiple interpretors? )
> Is this still true (please tell me it's been fixed)?
> if so, where can I get this patch and how do I apply it?

Follow the link to TnFOX given in the FAQ. Then study FXPython - 
heavily - and with a very fine toothed comb.

> I asked about multi-threading and boost python in on this list a while ago,
> and got no answer. I took this a a "go ahead, no problems". If I am being an
> idiot, could you tell me so? Just flame away at me so I know I've been
> stupid. 

I remember your question, and I didn't answer because the FAQ answers 
and I don't have the time to answer FAQ answered questions. I think 
the Boost.Python homepage could do with a large flashing neon sign 
saying "CHECK THE FAQ BEFORE ASKING A QUESTION" right before "SEARCH 
THE C++ SIG MAILING LIST ARCHIVES BEFORE ASKING A QUESTION".

Had you done either, you would have known the answer.

Now with the berating being done, I must express my sympathies for 
your task. I wrapped TnFOX for Python using Boost.Python and it was 
extremely painful indeed. It can be done, but expect at least 200 
hours of programmer time to wrap your head around it. Once you know 
what you're doing, it becomes quite easy.

> A lot of people here actually know what they are doing. I do not
> have that luxury.  I am finding boost python extremely complex and
> non-intuitive.  There is also a lack of good documentation (example code is
> nice to have, but does not constitute proper documentation all by itself).

Actually, the docs are pretty good. I would have cut out my own 
tongue to admit that a few years ago, but the problem is not the 
documentation - it's the programmer thinking in old style C++ ways.

Once you wrap your head around Boost.Python, it becomes quite 
intuitive. I can now happilly plug around its internals and do 
anything I like fairly confidently. It's actually quite a simple & 
intuitive design though I do wish there were more usage examples out 
there - and also I wish more interfaces were publicly defined & 
solid.

Now I have designed the machinery needed to get threaded C++ and 
Python working. It took me months, and it's not pretty at all and 
rather easy to break if you modify it. But copying me would be the 
easiest by far.

BTW I reckon your problems stem from the GIL not only being a lock 
but also being a state variable for Python. This state varies, 
unpredictably, during and between locks whenever you touch Python at 
all (including via any other thread). Touching BPL in any way usually 
means touching Python, so basically dragons abound here.

This will explain the often erratic & weird ordering of actions in 
FXPython in TnFOX - I worked it out after many hours in the debugger 
watching Python, C++, and Boost.Python interact. I suggest you copy 
my form closely in your endeavours.

Good luck!

Cheers,
Niall