Thanks for the response. On Sat, Dec 1, 2012 at 5:23 PM, Alexander Kjeldaas <alexander.kjeld...@gmail.com> wrote: > > What I've mostly done in similar circumstances (jni) > > 1. Create an interface (virtual functions or template) for the FFI in C++ > that covers everything you use. Then create one test implementation and one > real implementation. The test implementation must allocate resources > whenever the real FFI does so. Doing memory allocation works. This makes it > possible to test all your FFI in C++ using valgrind.
If I understand correctly, this sounds like what I was talking about, i.e. to stub out the C++ side and drive that from haskell to try to repro. That way I don't have to have windows popping up and do the simulation at the level of mouse clicks. The danger is that it turns out to be lots of work to implement, but still somehow doesn't reproduce the problem. That could happen if the bug is in C++, but only turns up during manual manipulation. Or maybe you're talking about the other way around, stub out the haskell and replace it with C++ and then run that in valgrind? That seems unlikely to be helpful, because if the bug is in the haskell FFI code then rewriting that all in C++ is just going to replace it with possibly also buggy C++ code. It seems to me like valgrind just plain doesn't work for haskell, maybe because the ghc runtime uses its own allocator? So if the bug is in haskell I can't find it with valgrind. If the bug is in C++, well, I already have a pure C++ version (that talks to the C++ interface in a very simplistic way), and it can run under valgrind, which doesn't turn up any out of bounds errors. > 2. Add tracing support to the real implementation and replay support to the > test implementation. I'm not sure this would work, since the whole thing is that the bug is nondeterministic. I feel like the only way to get it to come out is to do a bunch of random stuff for a period of time. It's likely that whether it happens or not depends on the memory layout for that particular run, and as far as I know you can't make that consistent. Or can you? > 3. Upload to Hackage. Is the suggestion that people who love debugging hard problems will swarm out of the woodwork and help me find the problem? I should be so lucky :) _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe