The pthread_cond_clockwait function was recently added[1] to glibc, and is due to be released in glibc 2.30. If this function is available in the C library it can be used it to fix https://gcc.gnu.org/bugzilla/show_bug.cgi?id=41861 by supporting std::chrono::steady_clock properly with std::condition_variable.
This means that code using std::condition_variable::wait_for or std::condition_variable::wait_until with std::chrono::steady_clock is no longer subject to timing out early or potentially waiting for much longer if the system clock is warped at an inopportune moment. If pthread_cond_clockwait is available then std::chrono::steady_clock is deemed to be the "best" clock available which means that it is used for the relative wait_for calls and absolute wait_until calls using user-defined clocks. Calls explicitly using std::chrono::system_clock continue to use CLOCK_REALTIME via __gthread_cond_timedwait. If pthread_cond_clockwait is not available then std::chrono::system_clock is deemed to be the "best" clock available which means that the previous suboptimal behaviour remains. [1] https://sourceware.org/git/?p=glibc.git;a=commit;h=afe4de7d283ebd88157126c5494ce1796194c16e libstdc++-v3/ * include/std/condition_variable: Add include of <bits/c++config.h> to make _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT available. (condition_variable): Split __clock_t into __system_clock_t, which is always system_clock and __best_clock_t, which is the clock that we wish to convert arbitrary other clocks to. If we know that pthread_cond_clockwait is available then it is best to convert clocks to steady_clock, otherwise it's best to use system_clock. (wait_until): If pthread_cond_clockwait is available, provide a steady_clock overload. Convert previous __clock_t overload to use __system_clock_t. Convert generic overload to convert passed clock to __best_clock_t. (wait_until_impl): Add steady_clock overload that calls pthread_cond_clockwait. Convert previous __clock_t overload to use __system_clock_t. (condition_variable_any): Use steady_clock for __clock_t if pthread_cond_clockwait is available. * acinclude.m4: Detect the availability of POSIX-proposed pthread_cond_clockwait function. * configure: Likewise. * configure.ac: Likewise. * config.h.in: Add _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT define to indicate presence of pthread_cond_clockwait function. --- libstdc++-v3/ChangeLog | 25 +++++++- libstdc++-v3/acinclude.m4 | 31 ++++++++- libstdc++-v3/config.h.in | 3 +- libstdc++-v3/configure | 83 ++++++++++++++++++++++- libstdc++-v3/configure.ac | 3 +- libstdc++-v3/include/std/condition_variable | 52 ++++++++++++-- 6 files changed, 191 insertions(+), 6 deletions(-) diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index a52a704..597000b 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,5 +1,30 @@ 2019-07-15 Mike Crowe <m...@mcrowe.com> + * include/std/condition_variable: Add include of <bits/c++config.h> + to make _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT available. + (condition_variable): Split __clock_t into __system_clock_t, which + is always system_clock and __best_clock_t, which is the clock that + we wish to convert arbitrary other clocks to. If we know that + pthread_cond_clockwait is available then it is best to convert + clocks to steady_clock, otherwise it's best to use + system_clock. (wait_until): If pthread_cond_clockwait is available, + provide a steady_clock overload. Convert previous __clock_t + overload to use __system_clock_t. Convert generic overload to + convert passed clock to __best_clock_t. (wait_until_impl): Add + steady_clock overload that calls pthread_cond_clockwait. Convert + previous __clock_t overload to use + __system_clock_t. (condition_variable_any): Use steady_clock for + __clock_t if pthread_cond_clockwait is available. + + * acinclude.m4: Detect the availability of POSIX-proposed + pthread_cond_clockwait function. + * configure: Likewise. + * configure.ac: Likewise. + * config.h.in: Add _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT define to + indicate presence of pthread_cond_clockwait function. + +2019-07-15 Mike Crowe <m...@mcrowe.com> + * testsuite/30_threads/condition_variable/members/2.cc (test01): Parameterise so that test can be run against an arbitrary clock. (main): Test using std::chrono::steady_clock and a user-defined diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4 index 24145fd..35979e7 100644 --- a/libstdc++-v3/acinclude.m4 +++ b/libstdc++-v3/acinclude.m4 @@ -4194,6 +4194,37 @@ AC_DEFUN([GLIBCXX_CHECK_PTHREADS_NUM_PROCESSORS_NP], [ ]) dnl +dnl Check whether pthread_cond_clockwait is available in <pthread.h> for std::condition_variable to use, +dnl and define _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT. +dnl +AC_DEFUN([GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT], [ + + AC_LANG_SAVE + AC_LANG_CPLUSPLUS + ac_save_CXXFLAGS="$CXXFLAGS" + CXXFLAGS="$CXXFLAGS -fno-exceptions" + ac_save_LIBS="$LIBS" + LIBS="$LIBS -lpthread" + + AC_MSG_CHECKING([for pthread_cond_clockwait]) + AC_CACHE_VAL(glibcxx_cv_PTHREAD_COND_CLOCKWAIT, [ + GCC_TRY_COMPILE_OR_LINK( + [#include <pthread.h>], + [pthread_mutex_t mutex; pthread_cond_t cond; struct timespec ts; int n = pthread_cond_clockwait(&cond, &mutex, 0, &ts);], + [glibcxx_cv_PTHREAD_COND_CLOCKWAIT=yes], + [glibcxx_cv_PTHREAD_COND_CLOCKWAIT=no]) + ]) + if test $glibcxx_cv_PTHREAD_COND_CLOCKWAIT = yes; then + AC_DEFINE(_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT, 1, [Define if pthread_cond_clockwait is available in <pthread.h>.]) + fi + AC_MSG_RESULT($glibcxx_cv_PTHREAD_COND_CLOCKWAIT) + + CXXFLAGS="$ac_save_CXXFLAGS" + LIBS="$ac_save_LIBS" + AC_LANG_RESTORE +]) + +dnl dnl Check whether sysctl is available in <pthread.h>, and define _GLIBCXX_USE_SYSCTL_HW_NCPU. dnl AC_DEFUN([GLIBCXX_CHECK_SYSCTL_HW_NCPU], [ diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in index 99286e6..3d13402 100644 --- a/libstdc++-v3/config.h.in +++ b/libstdc++-v3/config.h.in @@ -991,6 +991,9 @@ /* Define if pthreads_num_processors_np is available in <pthread.h>. */ #undef _GLIBCXX_USE_PTHREADS_NUM_PROCESSORS_NP +/* Define if pthread_cond_clockwait is available in <pthread.h>. */ +#undef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT + /* Define if POSIX read/write locks are available in <gthr.h>. */ #undef _GLIBCXX_USE_PTHREAD_RWLOCK_T diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure index ab46399..c0b98d8 100755 --- a/libstdc++-v3/configure +++ b/libstdc++-v3/configure @@ -21581,6 +21581,89 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu +# For pthread_cond_clockwait + + + + ac_ext=cpp +ac_cpp='$CXXCPP $CPPFLAGS' +ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5' +ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5' +ac_compiler_gnu=$ac_cv_cxx_compiler_gnu + + ac_save_CXXFLAGS="$CXXFLAGS" + CXXFLAGS="$CXXFLAGS -fno-exceptions" + ac_save_LIBS="$LIBS" + LIBS="$LIBS -lpthread" + + { $as_echo "$as_me:${as_lineno-$LINENO}: checking for pthread_cond_clockwait" >&5 +$as_echo_n "checking for pthread_cond_clockwait... " >&6; } + if test "${glibcxx_cv_PTHREAD_COND_CLOCKWAIT+set}" = set; then : + $as_echo_n "(cached) " >&6 +else + + if test x$gcc_no_link = xyes; then + cat confdefs.h - <<_ACEOF >conftest.$ac_ext +/* end confdefs.h. */ +#include <pthread.h> +int +main () +{ +pthread_mutex_t mutex; pthread_cond_t cond; struct timespec ts; int n = pthread_cond_clockwait(&cond, &mutex, 0, &ts); + ; + return 0; +} +_ACEOF +if ac_fn_cxx_try_compile "$LINENO"; then : + glibcxx_cv_PTHREAD_COND_CLOCKWAIT=yes +else + glibcxx_cv_PTHREAD_COND_CLOCKWAIT=no +fi +rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext +else + if test x$gcc_no_link = xyes; then + as_fn_error "Link tests are not allowed after GCC_NO_EXECUTABLES." "$LINENO" 5 +fi +cat confdefs.h - <<_ACEOF >conftest.$ac_ext +/* end confdefs.h. */ +#include <pthread.h> +int +main () +{ +pthread_mutex_t mutex; pthread_cond_t cond; struct timespec ts; int n = pthread_cond_clockwait(&cond, &mutex, 0, &ts); + ; + return 0; +} +_ACEOF +if ac_fn_cxx_try_link "$LINENO"; then : + glibcxx_cv_PTHREAD_COND_CLOCKWAIT=yes +else + glibcxx_cv_PTHREAD_COND_CLOCKWAIT=no +fi +rm -f core conftest.err conftest.$ac_objext \ + conftest$ac_exeext conftest.$ac_ext +fi + +fi + + if test $glibcxx_cv_PTHREAD_COND_CLOCKWAIT = yes; then + +$as_echo "#define _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT 1" >>confdefs.h + + fi + { $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_PTHREAD_COND_CLOCKWAIT" >&5 +$as_echo "$glibcxx_cv_PTHREAD_COND_CLOCKWAIT" >&6; } + + CXXFLAGS="$ac_save_CXXFLAGS" + LIBS="$ac_save_LIBS" + ac_ext=c +ac_cpp='$CPP $CPPFLAGS' +ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5' +ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5' +ac_compiler_gnu=$ac_cv_c_compiler_gnu + + + ac_fn_c_check_header_mongrel "$LINENO" "locale.h" "ac_cv_header_locale_h" "$ac_includes_default" if test "x$ac_cv_header_locale_h" = xyes; then : diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac index 80d8202..ad4ae0c 100644 --- a/libstdc++-v3/configure.ac +++ b/libstdc++-v3/configure.ac @@ -220,6 +220,9 @@ GLIBCXX_ENABLE_LIBSTDCXX_TIME # Check for tmpnam which is obsolescent in POSIX.1-2008 GLIBCXX_CHECK_TMPNAM +# For pthread_cond_clockwait +GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT + AC_LC_MESSAGES # For hardware_concurrency diff --git a/libstdc++-v3/include/std/condition_variable b/libstdc++-v3/include/std/condition_variable index a83996a..0e1bdf7 100644 --- a/libstdc++-v3/include/std/condition_variable +++ b/libstdc++-v3/include/std/condition_variable @@ -35,6 +35,7 @@ # include <bits/c++0x_warning.h> #else +#include <bits/c++config.h> #include <chrono> #include <bits/std_mutex.h> #include <bits/unique_lock.h> @@ -65,8 +66,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION /// condition_variable class condition_variable { - typedef chrono::system_clock __clock_t; typedef chrono::steady_clock __steady_clock_t; +#if defined(_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT) + typedef chrono::steady_clock __best_clock_t; +#else + typedef chrono::system_clock __best_clock_t; +#endif + typedef chrono::system_clock __system_clock_t; typedef __gthread_cond_t __native_type; #ifdef __GTHREAD_COND_INIT @@ -101,10 +107,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION wait(__lock); } +#if defined(_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT) + template<typename _Duration> + cv_status + wait_until(unique_lock<mutex>& __lock, + const chrono::time_point<__steady_clock_t, _Duration>& __atime) + { return __wait_until_impl(__lock, __atime); } +#endif + template<typename _Duration> cv_status wait_until(unique_lock<mutex>& __lock, - const chrono::time_point<__clock_t, _Duration>& __atime) + const chrono::time_point<__system_clock_t, _Duration>& __atime) { return __wait_until_impl(__lock, __atime); } template<typename _Clock, typename _Duration> @@ -112,9 +126,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION wait_until(unique_lock<mutex>& __lock, const chrono::time_point<_Clock, _Duration>& __atime) { - // DR 887 - Sync unknown clock to known clock. const typename _Clock::time_point __c_entry = _Clock::now(); - const __clock_t::time_point __s_entry = __clock_t::now(); + const __best_clock_t::time_point __s_entry = __best_clock_t::now(); const auto __delta = __atime - __c_entry; const auto __s_atime = __s_entry + __delta; @@ -171,10 +184,33 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { return &_M_cond; } private: +#if defined(_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT) + template<typename _Dur> + cv_status + __wait_until_impl(unique_lock<mutex>& __lock, + const chrono::time_point<__steady_clock_t, _Dur>& __atime) + { + auto __s = chrono::time_point_cast<chrono::seconds>(__atime); + auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s); + + __gthread_time_t __ts = + { + static_cast<std::time_t>(__s.time_since_epoch().count()), + static_cast<long>(__ns.count()) + }; + + pthread_cond_clockwait(&_M_cond, __lock.mutex()->native_handle(), + CLOCK_MONOTONIC, + &__ts); + + return (__steady_clock_t::now() < __atime + ? cv_status::no_timeout : cv_status::timeout); + } +#endif template<typename _Dur> cv_status __wait_until_impl(unique_lock<mutex>& __lock, - const chrono::time_point<__clock_t, _Dur>& __atime) + const chrono::time_point<__system_clock_t, _Dur>& __atime) { auto __s = chrono::time_point_cast<chrono::seconds>(__atime); auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s); @@ -188,7 +224,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION __gthread_cond_timedwait(&_M_cond, __lock.mutex()->native_handle(), &__ts); - return (__clock_t::now() < __atime + return (__system_clock_t::now() < __atime ? cv_status::no_timeout : cv_status::timeout); } }; @@ -208,7 +244,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION // Like above, but mutex is not required to have try_lock. class condition_variable_any { +#if defined(_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT) + typedef chrono::steady_clock __clock_t; +#else typedef chrono::system_clock __clock_t; +#endif condition_variable _M_cond; shared_ptr<mutex> _M_mutex; -- git-series 0.9.1
