On 31 Jan 2012 at 16:44, Davidson, Josh wrote: > Ok, well I did figure out the discrepancy between these extensions and > previous extensions that have been built that required setting > RTLD_GLOBAL. What I'm doing for these extensions is instead of building > in all of the original C++ code AND the Py++ generated code into the > extension, I'm only building in the Py++ generated sources and linking > an existing shared library containing the original C++ definitions. Is > this non-standard or bad practice?
The big problem with shared objects exporting lots of symbols was that the Linux runtime shared object linker used to have O(N^3) complexity. As a result, every time you ran a program linking to a ginormous shared object you'd get a pause of several seconds as it bound the symbols. Now, some years ago with KDE and OpenOffice taking forever to load, some eyeballs were turned onto this problem and I know they were going to get it down to O(N^2). There was speak of replacing bits with O(N), but it would introduce ABI compat problems among other things. Another angle was making it use multiple cores. My attention ended up moving elsewhere so I have no idea what has happened since. It could still be O(N^2), it could be O(N) or somewhere in between. > One issue with this is I'm now forced to deliver both the Python > extension shared libraries and the original shared libraries. Not a > huge deal, but it does add a little work on the deployment and > maintenance end. On systems with sane DLL designs like Windows and Mac OS X, you'd generally keep the Python bindings separate from the library being bound as it's cleaner and more self-contained. You can also issue smaller self-container ABI compatible releases as hotfixes etc etc. On the insanity that is ELF, generally you can make inter-SO problems go away by linking everything into a ginormous monolithic SO. However you used to get that O(N^3)/O(N^2) problem I mentioned and maybe you still do. So, sometimes you just have to get your hands dirty and start with hack scripts which post-process the SOs to make their symbol tables sane, or write your own SO loader and binder implementation using dlopen() et al and bypass the system linker altogether :) Sadly the ISO standards work to enforce sanity in shared libraries across all platforms got dropped from C11 and C++11, but I certainly will try to push that forward again for C11 TR1 along with a few other items on my shopping list (I'm the ISO SC22 convenor for Ireland, though Ireland is only an observer). The problem, as always, is a lack of sponsorship or funding by anyone who cares enough to have the problem fixed properly - and it is a difficult problem to get correct. In the end, as much as these problems are annoying and cost time to people like you, the cost of fixing them isn't seen as business relevant by those with the resources. HTH, Niall -- Technology & Consulting Services - ned Productions Limited. http://www.nedproductions.biz/. VAT reg: IE 9708311Q. Company no: 472909. _______________________________________________ Cplusplus-sig mailing list Cplusplus-sig@python.org http://mail.python.org/mailman/listinfo/cplusplus-sig
