| Message ID | YVdk+kdg/7AItMeb@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | [committed] libstdc++: Make std::jthread support pointers to member functions [PR 100612] | expand |
On Fri, 1 Oct 2021 at 23:19, Jonathan Wakely via Libstdc++ <libstdc++@gcc.gnu.org> wrote: > > This adds a non-standard extension to support initializing a > std::jthread with a pointer to a member function that expects a > stop_token to be added to the arguments. That use case is not supported > by C++20, because the stop_token would get added as the first argument, > which is where the object argument needs to be to invoke a pointer to > member function. Yeah, and the use-case is supported by applying a wrapper that does the right kind of argument binding, like shown in the BZ. Why are we doing this?
On Fri, 1 Oct 2021 at 21:26, Ville Voutilainen wrote: > > On Fri, 1 Oct 2021 at 23:19, Jonathan Wakely via Libstdc++ > <libstdc++@gcc.gnu.org> wrote: > > > > This adds a non-standard extension to support initializing a > > std::jthread with a pointer to a member function that expects a > > stop_token to be added to the arguments. That use case is not supported > > by C++20, because the stop_token would get added as the first argument, > > which is where the object argument needs to be to invoke a pointer to > > member function. > > Yeah, and the use-case is supported by applying a wrapper that does > the right kind of argument binding, like > shown in the BZ. Why are we doing this? The lambda workaround is not as convenient as having it Just Work. so it seemed like a useful extension to try, with no downside. It doesn't even change the is_constructible<thread, ...> result , because the std::thread constructor isn't constrained, so is_constructible<thread, ...> is true for nearly all arg types anyway. The only "non-conformance" is that we don't diagnose the is_invocable_v<decay_t<F>, decay_t<Args>...> requirement if F is a pointer-to-member-function. Maybe I should have sent it as an RFC, or just left it in my fork not pushed to trunk. If a proposal comes before the committee and gets rejected then we can remove it again.
diff --git a/libstdc++-v3/include/std/thread b/libstdc++-v3/include/std/thread index f51392ab42c..46519086aae 100644 --- a/libstdc++-v3/include/std/thread +++ b/libstdc++-v3/include/std/thread @@ -99,6 +99,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION #ifdef __cpp_lib_jthread +#ifndef __STRICT_ANSI__ + template<typename _Callable, typename... _Args> + constexpr bool __pmf_expects_stop_token = false; + + template<typename _Callable, typename _Obj, typename... _Args> + constexpr bool __pmf_expects_stop_token<_Callable, _Obj, _Args...> + = __and_<is_member_function_pointer<remove_reference_t<_Callable>>, + is_invocable<_Callable, _Obj, stop_token, _Args...>>::value; +#endif + /// A thread that can be requested to stop and automatically joined. class jthread { @@ -211,6 +221,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION static thread _S_create(stop_source& __ssrc, _Callable&& __f, _Args&&... __args) { +#ifndef __STRICT_ANSI__ + if constexpr (__pmf_expects_stop_token<_Callable, _Args...>) + return _S_create_pmf(__ssrc, __f, std::forward<_Args>(__args)...); + else +#endif if constexpr(is_invocable_v<decay_t<_Callable>, stop_token, decay_t<_Args>...>) return thread{std::forward<_Callable>(__f), __ssrc.get_token(), @@ -226,6 +241,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION } } +#ifndef __STRICT_ANSI__ + template<typename _Callable, typename _Obj, typename... _Args> + static thread + _S_create_pmf(stop_source& __ssrc, _Callable __f, _Obj&& __obj, + _Args&&... __args) + { + return thread{__f, std::forward<_Obj>(__obj), __ssrc.get_token(), + std::forward<_Args>(__args)...}; + } +#endif + stop_source _M_stop_source; thread _M_thread; }; diff --git a/libstdc++-v3/testsuite/30_threads/jthread/100612.cc b/libstdc++-v3/testsuite/30_threads/jthread/100612.cc new file mode 100644 index 00000000000..d6c81706b8f --- /dev/null +++ b/libstdc++-v3/testsuite/30_threads/jthread/100612.cc @@ -0,0 +1,24 @@ +// { dg-options "-std=gnu++20" } +// { dg-do compile { target c++20 } } +// { dg-additional-options "-pthread" { target pthread } } +// { dg-require-gthreads "" } + +#include <thread> + +void +test_pfm() +{ + // PR libstdc++/100612 + struct X + { + void run(std::stop_token) { } + void run_arg(int) { } + void run_args(std::stop_token, int, int) { } + }; + + X x; + + std::jthread{&X::run, &x}; + std::jthread{&X::run_arg, &x, 1}; + std::jthread{&X::run_args, &x, 1, 1}; +}