http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54847
--- Comment #42 from Jeremy Huddleston Sequoia <jeremyhu at macports dot org> 2012-10-08 20:10:26 UTC --- (In reply to comment #41) > (In reply to comment #40) > > I still don't see why the _POSIX_TIMERS > 0 check exists at all. On systems > > that don't have it, the tests will simply fail because timespec or nanosleep > > are undefined. > > The existence of a function called nanosleep doesn't mean it's the right one, > or that it will be found at link time, or available at run-time. > > Checking _POSIX_TIMERS > 0 means the functionality is actually usable, without > checking sysconf() at run-time as described by POSIX.1b-2001. > Right, but as we see here, the converse is not true. ie: This is true: (_POSIX_TIMERS > 0) => (nanosleep is the one you want) This is not true: (nanosleep is the one you want) => (_POSIX_TIMERS > 0) You want to find an test such that: (your test) <=> (nanosleep is the one you want) > (That was a link to clock_nanosleep not nanosleep, which was a different > option, not Timers ;) Aww sorry. I copy-linked the wrong one, but meh. > ... but you do still seem to doubt that the struct is unnecessary in C++. No. I don't doubt that. I admitted in comment #20 that C++ is not a strength of mine, so thanks for letting me know about this detail. > Maybe you've noticed how you don't need to say: > > class std::string str = "a string"; > ^^^^^ > to use C++ classes. It's the same for structs. Yeah, I knew about class, but I didn't know about that for structs. I thought it wasn't possible to drop 'struct' in C++ as it's not possible to drop it in C (although most users will typedef). Thanks for teaching me something new. > Again, there's a difference between *working* (i.e. being usable) on darwin > and > being able to build libstdc++ with a different compiler. There is no > requirement to be able to configure libstdc++ with anything other than G++, > but > in any case I assure you that clang++ doesn't require the 'struct' keyword > either. I don't doubt it. I was just trying to make the usage strictly match the POSIX spec. > > It's not one system. You are misreading the spec. > > No I'm not, my words you quoted carefully made the distinction of saying -1 > means the Timers option is not supported, not that nanosleep is not supported: Ok. > I'd be happy to improve the test to support other systems, but the patches > posted to this PR so far have been unacceptable due to failing to understand > the existing checks, failing to meet libstdc++'s configury conventions, or > adding support for a single system rather than for any systems which provide > nanosleep without the rest of the Timers option. In the absence of a decent > patch I suggest defining the HAVE_NANOSLEEP macro in os_defines.h and moving > on. > > Why are you even othering to put that code inside of a _POSIX_TIMERS > 0 > > check. > > If _POSIX_TIMERS > 0, you're guaranteed (by the standard) to have that > > functionality, so there's no point in checking... > > The existence of a preprocessor symbol doesn't tell you whether you need to > link to a particular library to use the function. Ah, I forgot you were checking for library linkage as well. That makes sense. > The check is AC_TRY_LINK which will ensure not only is the function declared > but the symbol is found, having added -lposix4 or -lrt to the link line if > earlier checks indicate they're needed. That makes sense. > > if you want to support all > > platforms, it's better to just check for nanosleep directly without the > > _POSIX_TIMERS check. > > If _POSIX_TIMERS is defined to 0 the code might compile but not work at > run-time. I didn't write those checks, but I'm not inclined to remove the > tests of the POSIX option macros just to fix this PR. Ok, what about just using _POSIX_TIMERS > 0 || defined(__APPLE__)? That may miss some other OSs in the same boat, but they can always add similar checks.
