Hi Giuseppe, thanks for answering and sorry for the delayed response. Easter holidays :-)
Giuseppe Corbelli <giuseppe.corbe...@copanitalia.com> wrote on 28.03.2013 09:37:39: > On 26/03/2013 18:51, Holger Joukl wrote: > > > > Hi, > > > > I'm wrapping a C++ library that's actually just a thin wrapper around a C > > lib. > > > > Through a dispatch() method of a Dispatcher class there's an invocation of > > callbacks which get implemented on the Python side, by subclassing callback > > classes exposed through Boost.Python. > > > > Now, for performing the actual dispatch the C++ library calls into the > > underlying C library. > > > > This hasn't been a problem so far as we've been targetting Solaris using > > Sun/Oracle studio > > compilers. > > > > However, on Linux compiled with GCC, if an exception gets raised in the > > Python callback the > > program segfaults. Obviously the C part of the vendor library has not been > > compiled with > > (GCC-) exception support for Linux. > > > > Unfortunately this isn't under my control and the library provider seems > > not to be willing > > to make the library robust against exceptions in user callback code. > > > > So I need to keep the Boost C++ exception that "signals" the Python > > exception from passing > > through the C parts. > > How does the library handle callbacks? An event loop in a separate thread? Do > you have to explicitly call some blocking function to run the event loop? Yes. There's a separate thread that schedules events to a queue being dispatch in the main loop, in the main thread. And yes, there's a blocking call to a dispatch method with the possibility of a timeout or alternatively a non-blocking poll call (we make sure to properly release & reacquire the Python GIL during blocking). > If it's a C lib likely the callbacks are just function pointers. Being called > inside a C object I'd say you assumption is correct: no C++ exceptions to be > raised inside callbacks (the lib is gcc-compiled, it has no knowledge of > exceptions). Correct, the callbacks are function pointers from the C libs point of view. > If you could recompile with g++ the exception would raise from the > event loop, > unless catched while calling the callback function pointer. While I do have the C++ sources (to be able to recompile for different C++ compilers) I don't have the C sources so I unfortunately I can't recompile the C-lib parts with exceptions support. Sidenote: For Oracle/Sun Solaris Studio compilers this isn't a problem as you basically can't and don't need to switch the exception support of the compiler for mixing C and C++ code (http://www.oracle.com/technetwork/articles/servers-storage-dev/mixingcandcpluspluscode-305840.html) > Sidenote: how does the C++ exception mechanism work under the hood? What > happens if it's called inside a C compiled function? Not sure if I understand your question correctly, but: - Solaris Studio compilers: An exception raised in a C++ compiled function that got called from a C compiled function called from a C++ main will properly propagate to the main caller - GCC: An exception raised in a C++ compiled function that got called from a C compiled function called from a C++ main will - segfault if the C compiled function hasn't been compiled with exception support (-fexceptions) - properly propagate to the main caller if the C compiled function has been compiled with exception support Holger Landesbank Baden-Wuerttemberg Anstalt des oeffentlichen Rechts Hauptsitze: Stuttgart, Karlsruhe, Mannheim, Mainz HRA 12704 Amtsgericht Stuttgart _______________________________________________ Cplusplus-sig mailing list Cplusplus-sig@python.org http://mail.python.org/mailman/listinfo/cplusplus-sig
