Re: at_init / at_exit proposal

Hi Dirk,

Dirk Gerrits <[email protected]> writes:

> Boost.Python currently uses some global/static variables that cause
> problems in embedding. (Basically you can't call Python's cleanup
> routines because the variables would be cleaned up after Python
> itself, causing a crash.)
>
> I propose to add a mechanism like the following which I hope will help
> to fix this issue:
>
> struct at_init
> {
>      explicit at_init(function<void ()> f)
>      {
>          if (extending)
>              f();
>          else
>              /* register f somewhere to be called after
>              the interpreter starts */
>      }
> };

I can't imagine what we'd want this for.  Module import time is early
enough to initialize any state associated with a module, and the rest
of the state can safely live forever.

> struct at_exit
> {
>      function<void ()> m_f;
>
>      explicit at_exit(function<void ()> f)
>          : m_f(f)
>      {
>          if (embedding)
>              /* register f somewhere to be called before the
>              interpreter shuts down */
>      }
>
>      ~at_exit()
>      {
>          if (extending)
>              m_f();
>      }
> };

I don't understand the logic here.  Why would we want different
behavior for extending and embedding?

> Example usage:
> namespace {
>
> registry_t* registry;
> void create() { registry = new registry_t;
>                  /* initialization */ }
> void destroy() { delete registry; }
> at_init registry_creation(&create);
> at_exit registry_destruction(&destroy);
>
> registry_t& entries() { return *registry; }
> ..
> } // unnamed
>
> This will allow things to be done at interpreter startup and shutdown,
> like the conversion registry initialization and shutdown above.
>
> When extending, this is the same as the 'startup' and 'shutdown' of
> the translation unit.

I don't think we need to tear down the entire registry at shutdown.
It seems enough to reset all of the object()s and handle<>s it's
holding.


-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com