Other classes that have native_handle/typesizes.cc tests have native_type_handle defined as a pointer type, and the pointed-to type is native_handle, the type of the single data member of the class (*). It thus makes sense to check that the single data member and the enclosing class type have the same size and alignment: a pointer to the enclosing type should also be a valid pointer to its single member.
(*) this single data member is actually inherited or enclosed in another class, but let's not get distracted by this irrelevant detail. std::thread, however, does not follow this pattern. Not because the single data member is defined as a direct data member of a nested class, rather than inherited from another class. The key difference is that it does not use native_type_handle's pointed-to type as the single data member, it rather uses native_type_handle directly as the type of the single data member. On GNU/Linux, and presumably on most platforms, native_handle_type = __gthread_t is not even a pointer type. This key difference would have been obvious if remove_pointer<T> rejected non-pointer types, but that's not the case. When given __gthread_t -> pthread_t -> unsigned long int, remove_pointer<T>::type is T, so we get unsigned long int back. The test works because there's no pointer type to strip off. However, on a platform that defines __gthread_t as a pointer type, we use that pointer type as native_type_handle and as the type for the single data member of std::thread. But then, the test compares size and alignment of that type with those of the type obtained by removing one indirection level. We're comparing properties of different, unrelated types. Unless the pointed-to type happens to have, by chance, the size and alignment of a pointer, the test will fail. IOW, the test is no good: it's not testing what it should, and wherever it passes, it's by accident. In order to test what it should, we'd need to use an alternate test function that does not strip off one indirection level from native_handle_type, if the test is to remain. Should I introduce such an alternate test function and adjust the test, or just remove the broken test? Or should we change std::thread::native_handle_type to __gthread_t*, while keeping unchanged the type of the single data member std::thread::id::_M_thread? Thanks in advance, -- Alexandre Oliva, freedom fighter he/him https://FSFLA.org/blogs/lxo Be the change, be Free! FSF Latin America board member GNU Toolchain Engineer Free Software Evangelist Hay que enGNUrecerse, pero sin perder la terGNUra jamás - Che GNUevara
