FCD/Alsa bug (Re: Bug hunting)

Cross posting to discuss-gnuradio. The bug in question is that if you instanciate an alsa source on a busy device (opened by another app), then the program crashed. On 08/08/12 00:23, Dimitri Stolnikov wrote: [...] Yes, I started to investigate, and it seems to me that this is not a gr-osmosdr bug, but it's a gnuradio one, caused by gr-fcd. This simple test program have the same problem, yet it only uses gr-fcd. #include <iostream> #include <fcd_source_c.h> int main(int argc, char **argv) { fcd_source_c_sptr fsrc; try { fsrc = fcd_make_source_c("hw:2"); // KO, from gr-fcd } catch (std::runtime_error &e) { std::cerr << "Error!\n"; } exit(0); } g++ test.cc -o test -I/usr/local/include/gnuradio -lgnuradio-fcd Here is the log: audio_alsa_source[hw:2]: Device or resource busy Error! *** glibc detected *** /home/cgagneraud/sdr/gr-osmosdr/test: free(): invalid pointer: 0x08052e3c *** [...] And here is a cleaned up backtrace: operator delete gruel::msg_accepter::~msg_accepter checked_delete<gr_hier_block2> boost::detail::sp_counted_impl_p<gr_hier_block2>::dispose [...] const, boost::shared_ptr<gr_basic_block> > > >::~map __cxa_finalize __do_global_dtors_aux [...] main The problem is related to gnuradio-core/src/lib/runtime/gr_sptr_magic.{h,cc} and the static std::map in there. gr_hier_block2 ctor insert "this" in this map, but then in fcd_source ctor, audio_alsa_source ctor throws an exception, so "this" (gr_hier_block2/fcd_source) is not a valid pointer anymore. When the program exits, the map get cleanup up and free is called on this pointer. It's not possible to cleanup the map in fcd_source, because the dtor is not called when exception occurs in the ctor (which, btw, leads to some memory leaks in alsa_source: namely d_hw_params and d_sw_params). It's a bad idea to call fetch_initial_sptr(this) before throwing in the ctor, because it seems the object get deleted. Maybe one solution could be to add a function member to mark the hier_block2 as zombie, the gr_hier_block2 dtor could then cleanup the map depending on that information. A workaround could be to catch the exception in fcd_source ctor. and throw exceptions whenever the fcd C API returns FCD_MODE_NONE. Well, this is kind of a dirty trick that has lot of drawbacks. Maybe some gnuradio gurus could shed some light on how to address this issue? Chris -- Christian Gagneraud, Embedded systems engineer. Techworks Marine 1 Harbour road Dun Laoghaire Co. Dublin Ireland Tel: + 353 (0) 1 236 5990 Web: http://www.techworks.ie/