On 24 September 2013 02:22, Alan Modra wrote: > > Try compiling that testcase with -static rather than -Wl,--as-needed. > You'll hit std::system_error just like you do here. I believe that is > a libstdc++ bug, and can be solved by making libstdc++.a use strong > references to pthread symbols from std::thread::join() (and perhaps > other objects that provide c++ thread support, if there are such).
It's the std::thread constructor template that needs pthread_create. std::thread::join() needs pthread_join. It's complicated by the fact that the source code doesn't mention pthread_create, it uses __gthread_create instead, which is the weak reference. > libstdc++.a objects that are just testing "is this program threaded" > should continue to use weak references. > > Solving the problem with --as-needed and libstdc++.so isn't so easy. > One solution might be to split off thread support from libstdc++.so.6. Yes, I've suggested that before. It has the additional benefit that users don't need to say -pthread to use C++11 threads (they shouldn't need to care that it uses pthreads under the covers) they could just say something like -lstdc++thr where that lib would depend on libpthread.so. It has the huge disadvantage of breaking the ABI by removing symbols from libstdc++.so > Otherwise we'd need to solve the transitive reference somehow. > ie. Teach the linker that a reference to std::thread::join() means > that pthread_create is required. One obvious way to do that is have > the compiler reference pthread_create in objects that use > std::thread::join(). How would we have the compiler do that?
