[C++-sig] Can boost_python dll be delay loaded?

[Niall Douglas]

On 30 Jul 2010 at 10:56, David Aldrich wrote:

> > I thought that the application installer registered the DLL manifests
> > at their locations? It's like registering COM or .NET objects, in
> > fact I think it's the same mechanism nowadays.
> 
> Well, I don't plan to use an application installer. Most of our users
> build and run the application from within a svn working copy. 

It's usually easy enough to rig up a COM object registration into a 
build system. Surely it would similar for manifest stuff.

> > As for why it doesn't work when others do, I would guess it's due to
> > how the BPL machinery sets itself up on process init. During static
> > init the BPL library sets up all sorts of runtime information which
> > is later used by BPL clients, and during all of this it is extremely
> > important that everything be kept in precisely the right order.
> 
> I don't understand the intricacies of Boost's initialisation, nor do I
> even know when it happens. I naively thought that nothing would happen
> until I explicitly call a boost_python API method. Does the fact that I
> have included <boost/python.hpp> mean that some boost initialisation
> will occur before main() is reached? 

Rather it is when the BPL DLL is loaded into the process that it 
performs its static init which sets up the internal environment ready 
for your client code to call BPL APIs. The BPL DLL, like any complex 
metaprogrammed C++ DLL nowadays, will expect to be initialised before 
main() gets called and would be unlikely to work if main() gets 
called first.

> > Your best bet it would seem now is to have PATH
> > modified on app install, but that is a very lazy way out and is
> > indeed banned in lots of corporate environments. 
> 
> Sadly, I think that is the only solution. Thanks again for your help.

The only other I can think of is putting a symbolic link to the BPL 
DLL in the same directory as the executable. Symbolic links are Vista 
or later only sadly, though you could install Microsoft's Unix 
subsystem on XP and get symbolic links that way :)

HTH,
Niall

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