On 24 May 2013 21:10, Jakub Jelinek wrote: > > So, there is a minor issue that what is std::chrono::steady_clock has > changed, if you say use it as a function parameter, it will mangle > differently before/after. Guess not that big a deal, after all, C++11 > support is still experimental, right?
Right. > But the more important issue is that std::chrono::system_clock broke, > code compiled against the old headers will assume > std::chrono::system_clock::duration is microseconds resolution on Linux, > while code compiled against the new headers will assume it is in > nanoseconds resolution. That is because of: > #ifdef _GLIBCXX_USE_CLOCK_REALTIME > typedef chrono::nanoseconds duration; > #elif defined(_GLIBCXX_USE_GETTIMEOFDAY) > typedef chrono::microseconds duration; > #else > typedef chrono::seconds duration; > #endif > > Thus, I'm afraid we can't ABI compatibly change either of these macros, > unless we e.g. keep old std::chrono::system_clock as is and introduce > std::chrono::__whatever::system_clock or whatever, that will be typedefed > as std::chrono::system_clock. Or use the new ABI attribute so the "new" system_clock mangles differently to the "old" system_clock. I prefer to break it though - if we're going to paint ourselves into a corner and insist on compatibility with semi-functional previous releases we should stop calling it "experimental". Alternatively, while we still call it experimental, let's fix it properly and get it right. > Is it a big issue if system_clock will have > just old resolution (usec) and =auto code is reverted to only tweak > steady_clock (aka. _GLIBCXX_USE_CLOCK_MONOTONIC) (then for 4.8 the change > would be just to drop > ac_has_clock_realtime=yes > line from if test x"$ac_has_clock_monotonic_syscall" = x"yes"; then)? IMHO yes, that's a big issue. I believe most users are more interested in system_clock than in steady_clock, and we should provide a nanosecond-resolution system_clock if the OS supports it. > Ugh, C++ and ABI doesn't go well together... Yeah, this stuff's hard. But I hope we can get a stable ABI for 4.9, even if it's incompatible with previous releases.
