XS & exception handling

gjb has asked for the wisdom of the Perl Monks concerning the following question:

Dear fellow Monks,

After doing a supersearch, a scan of all relevant docs and a grep on the .xs files of all the modules I've installed on my machine I didn't get a clue, so I'd like to seek your collective wisdom.

I'm currently writing a Perl module that interfaces to a C++ library. In several functions of this library, exceptions are thrown of a type I know, so in the XS code I use

  try {
    ...
  } catch{MyException& e) {
    ...
  } catch(...) {
    ...
  }
[download]

to deal with it and to wrap the error message into a croak(...) for Perl consumption.

Upon testing it seems as if the C++ code throws the expected exception alright (this has been verified by the author of the C++ code), but in the XS code I can't catch that exception. However, something gets caught in the generic catch catch(...). I have turned on exception handling with the compiler option -GX.

Hence my question: has anyone successfully caught typed C++ exceptions in XS in this setup (NT 4.0 SP 5, ActiveState Perl 5.6.1 build 633, MSVC++ 6.0) or is there some advice you could offer?

Thanks in advance, -gjb-

Comment on XS & exception handling Select or Download Code

Replies are listed 'Best First'.
Re: XS & exception handling by Zaxo (Archbishop) on Jan 09, 2003 at 13:32 UTC
In gcc you can compile with the `-fexceptions` flag, which permits the C code to pass C++ exceptions along. That ability is not portable. Your best bet is to produce a C/C++ interface to the C++ library. Use `extern "C"` linkage qualifier, and the `throw()` exception specifier. Catch all exceptions and handle them by setting `errno` appropriately and returning an error flagging result like `PL_sv_undef`. I haven't tested the C++ compliance of MSVC6, but there is some chance that exception handling will be adequate. After Compline, Zaxo	[reply]
Re: XS & exception handling (C vs. C++) by tye (Sage) on Jan 09, 2003 at 18:36 UTC
I think Zaxo hit on the problem. Your *.xs code is compiled as C code not as C++ code. You can get XS to compile your code as C++ code. The last time I did this was quite some time ago so it required some hacking but wasn't very hard. I think that it is easy in modern versions of XS (like a "-C++" flag on the command line). - tye	[reply]
Re: XS & exception handling by broquaint (Abbot) on Jan 10, 2003 at 14:50 UTC
For some good discussions on C++ exceptions in XS checkout the p5p archive for example C++ Exceptions in XSUB. HTH `_________ broquaint`	[reply]
Re: XS & exception handling (pinpointed) by gjb (Vicar) on Jan 13, 2003 at 09:57 UTC
The problem has finally been pinpointed, thanks Zaxo, tye and broquaint for their suggestions. It turned out that the problem was in the library's C++ code. Internally, exceptions are caught using `try {...} catch(...) {...}` [download] In the catch, an error code is set, which is subsequently tested in the calling code (via a macro expansion) so that an exception is thrown (just don't ask, it's not my code). The problem is that in the original `catch` some logging is done which... yeah, right, generates an error and hence some exception is thrown that only got caught in the `catch(...)` of my XS code, completely bypassing the intended exception throwing/catching mechanism. Lessons learned: exceptions are handled as one would expect in this setup (NT, ActiveState Perl, MSVC++), never ever trust someone who says he tested his code (his test may be succesful, but simply not adequate to find the real problem). Thanks again to all who helped, -gjb-	[reply] [d/l] [select]