On Fri, 22 Aug 2025, 04:26 Nathan Myers, <n...@cantrip.org> wrote: > This moves std::tai_clock::now() and std::tai_clock::now() > definitions from header inlines to static members invoked via a > normal function call, in service of stabilizing the C++20 ABI. > > It marks tai_clock and gps_clock "is_steady = true", as they > are not subject to adjudicated discontinuities, unlike civil > time with annual spring and fall changes, and UTC with >
Please revert this part. is_steady has nothing to do with civil time or daylight savings transitions. irregular leap seconds. Even if no more UTC leap seconds > are ordered, as is likely, relating historical UTC time > points to an absolute reference depends on using a table > of past leap seconds, so utc_clock::is_steady remains false. > GPS time, by contrast, is at a constant offset from TAI. > > It changes #if guards to mention the actual __cpp_lib_* > feature gated, not just the language version, for clarity. > > New global function symbols std::chrono::tai_clock::now > and std::chrono::gps_clock::now are exported. > > libstdc++-v3/ChangeLog: > * include/std/chrono: Remove inline impls. > * src/c++20/clock.cc: New file for out-of-line impls. > * src/c++20/Makefile.in: Mention clock.cc > * src/c++20/Makefile.am: Mention clock.cc > --- > libstdc++-v3/include/std/chrono | 32 +++++++++--------- > libstdc++-v3/src/c++20/Makefile.am | 2 +- > libstdc++-v3/src/c++20/Makefile.in | 4 +-- > libstdc++-v3/src/c++20/clock.cc | 52 ++++++++++++++++++++++++++++++ > 4 files changed, 70 insertions(+), 20 deletions(-) > create mode 100644 libstdc++-v3/src/c++20/clock.cc > > diff --git a/libstdc++-v3/include/std/chrono > b/libstdc++-v3/include/std/chrono > index cb8213e2f9f..7fb5d4ec4c7 100644 > --- a/libstdc++-v3/include/std/chrono > +++ b/libstdc++-v3/include/std/chrono > @@ -22,6 +22,8 @@ > // see the files COPYING3 and COPYING.RUNTIME respectively. If not, see > // <http://www.gnu.org/licenses/>. > > +// [time] > + > /** @file include/chrono > * This is a Standard C++ Library header. > * @ingroup chrono > @@ -42,12 +44,16 @@ > # include <bits/c++0x_warning.h> > #else > > +#define __glibcxx_want_chrono > +#define __glibcxx_want_chrono_udls > +#include <bits/version.h> > + > #include <bits/chrono.h> > > -#if __cplusplus >= 202002L > +#if __cpp_lib_bitops >= 201907L > # include <bit> // __countr_zero > #endif > -#if __cplusplus >= 202002L && _GLIBCXX_HOSTED > +#if __cpp_lib_chrono >= 201803L && _GLIBCXX_HOSTED > # include <sstream> > # include <string> > # include <vector> > @@ -56,10 +62,6 @@ > # include <bits/unique_ptr.h> > #endif > > -#define __glibcxx_want_chrono > -#define __glibcxx_want_chrono_udls > -#include <bits/version.h> > - > namespace std _GLIBCXX_VISIBILITY(default) > { > _GLIBCXX_BEGIN_NAMESPACE_VERSION > @@ -79,7 +81,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > */ > namespace chrono > { > -#if __cplusplus >= 202002L > +#if __cpp_lib_chrono >= 201803L > /// @addtogroup chrono > /// @{ > struct local_t { }; > @@ -175,13 +177,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > using period = system_clock::period; > using duration = chrono::duration<rep, period>; > using time_point = chrono::time_point<tai_clock>; > - static constexpr bool is_steady = false; // XXX true for CLOCK_TAI? > + static constexpr bool is_steady = true; > > - // TODO move into lib, use CLOCK_TAI on linux, add extension point. > [[nodiscard]] > static time_point > - now() > - { return from_utc(utc_clock::now()); } > + now(); // in src/c++20/clock.cc > > template<typename _Duration> > [[nodiscard]] > @@ -215,13 +215,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION > using period = system_clock::period; > using duration = chrono::duration<rep, period>; > using time_point = chrono::time_point<gps_clock>; > - static constexpr bool is_steady = false; // XXX > + static constexpr bool is_steady = true; > > - // TODO move into lib, add extension point. > [[nodiscard]] > static time_point > - now() > - { return from_utc(utc_clock::now()); } > + now(); // in src/c++20/clock.cc > > template<typename _Duration> > [[nodiscard]] > @@ -3321,7 +3319,7 @@ namespace __detail > #endif // C++20 > } // namespace chrono > > -#if __cplusplus >= 202002L > +#if __cpp_lib_chrono >= 201803L > inline namespace literals > { > inline namespace chrono_literals > @@ -3350,7 +3348,7 @@ namespace __detail > _GLIBCXX_END_NAMESPACE_VERSION > } // namespace std > > -#if __cplusplus >= 202002L && _GLIBCXX_HOSTED > +#if __cpp_lib_chrono >= 201803L && _GLIBCXX_HOSTED > # include <bits/chrono_io.h> > #endif > > diff --git a/libstdc++-v3/src/c++20/Makefile.am > b/libstdc++-v3/src/c++20/Makefile.am > index 15e6f3445fb..736558ff24a 100644 > --- a/libstdc++-v3/src/c++20/Makefile.am > +++ b/libstdc++-v3/src/c++20/Makefile.am > @@ -36,7 +36,7 @@ else > inst_sources = > endif > > -sources = tzdb.cc format.cc atomic.cc > +sources = tzdb.cc format.cc atomic.cc clock.cc > > vpath % $(top_srcdir)/src/c++20 > > diff --git a/libstdc++-v3/src/c++20/Makefile.in > b/libstdc++-v3/src/c++20/Makefile.in > index d9e1615bbca..3cb6d6fea5f 100644 > --- a/libstdc++-v3/src/c++20/Makefile.in > +++ b/libstdc++-v3/src/c++20/Makefile.in > @@ -121,7 +121,7 @@ CONFIG_CLEAN_FILES = > CONFIG_CLEAN_VPATH_FILES = > LTLIBRARIES = $(noinst_LTLIBRARIES) > libc__20convenience_la_LIBADD = > -am__objects_1 = tzdb.lo format.lo atomic.lo > +am__objects_1 = tzdb.lo format.lo atomic.lo clock.lo > @ENABLE_EXTERN_TEMPLATE_TRUE@am__objects_2 = sstream-inst.lo > @GLIBCXX_HOSTED_TRUE@am_libc__20convenience_la_OBJECTS = \ > @GLIBCXX_HOSTED_TRUE@ $(am__objects_1) $(am__objects_2) > @@ -432,7 +432,7 @@ headers = > @ENABLE_EXTERN_TEMPLATE_TRUE@inst_sources = \ > @ENABLE_EXTERN_TEMPLATE_TRUE@ sstream-inst.cc > > -sources = tzdb.cc format.cc atomic.cc > +sources = tzdb.cc format.cc atomic.cc clock.cc > @GLIBCXX_HOSTED_FALSE@libc__20convenience_la_SOURCES = > @GLIBCXX_HOSTED_TRUE@libc__20convenience_la_SOURCES = $(sources) > $(inst_sources) > > diff --git a/libstdc++-v3/src/c++20/clock.cc > b/libstdc++-v3/src/c++20/clock.cc > new file mode 100644 > index 00000000000..2ba6e7fd28f > --- /dev/null > +++ b/libstdc++-v3/src/c++20/clock.cc > @@ -0,0 +1,52 @@ > +// std::chrono::tai_clock, gps_clock > + > +// Copyright (C) 2020-2025 Free Software Foundation, Inc. > +// > +// This file is part of the GNU ISO C++ Library. This library is free > +// software; you can redistribute it and/or modify it under the > +// terms of the GNU General Public License as published by the > +// Free Software Foundation; either version 3, or (at your option) > +// any later version. > + > +// This library is distributed in the hope that it will be useful, > +// but WITHOUT ANY WARRANTY; without even the implied warranty of > +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the > +// GNU General Public License for more details. > + > +// Under Section 7 of GPL version 3, you are granted additional > +// permissions described in the GCC Runtime Library Exception, version > +// 3.1, as published by the Free Software Foundation. > + > +// You should have received a copy of the GNU General Public License and > +// a copy of the GCC Runtime Library Exception along with this program; > +// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see > +// <http://www.gnu.org/licenses/>. > + > +// > +// ISO C++ 14882 > +// 30.7.4 [time.clock.tai], 30.7.5 [time.clock.gps] > +// P0355R7 > + > +#include <chrono> > + > +namespace std _GLIBCXX_VISIBILITY(default) > +{ > +_GLIBCXX_BEGIN_NAMESPACE_VERSION > + > +namespace chrono > +{ > +#if __cpp_lib_chrono >= 201803L && _GLIBCXX_HOSTED > + // TODO use CLOCK_TAI on linux, add extension point. > + time_point<tai_clock> > + tai_clock::now() > + { return from_utc(utc_clock::now()); } > + > + // TODO add extension point. > + time_point<gps_clock> > + gps_clock::now() > + { return from_utc(utc_clock::now()); } > +#endif > +} > + > +_GLIBCXX_END_NAMESPACE_VERSION > +} > -- > 2.50.1 > >
