From ad4d1d21ad5c515ba90355d13b14cbb74262edd2 Mon Sep 17 00:00:00 2001 From: Mike Crowe Date: Wed, 4 Sep 2019 22:43:29 +0000 Subject: [PATCH] PR libstdc++/41861 Add full steady_clock support to condition_variable The pthread_cond_clockwait function is available in glibc since the 2.30 release. If this function is available in the C library it can be used to fix PR libstdc++/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. 2019-09-04 Mike Crowe PR libstdc++/41861 * acinclude.m4 (GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT): Check for new pthread_cond_clockwait function. * configure.ac: Use GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT. * configure: Regenerate. * config.h.in: Regenerate. * include/std/condition_variable: (condition_variable): Rename __steady_clock_t typedef and add system_clock. Change __clock_t to be a typedef for the preferred clock to convert arbitrary other clocks to. [_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT] (wait_until): Add a steady_clock overload. (wait_until): Change __clock_t overload to use system_clock. [_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT] (__wait_until_impl): Add steady_clock overload that calls pthread_cond_clockwait. (__wait_until_impl): Change __clock_t overload to use system_clock. (condition_variable_any) [_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT]: Use steady_clock for __clock_t if pthread_cond_clockwait is available. From-SVN: r275390 --- libstdc++-v3/ChangeLog | 20 +++++ 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 | 62 ++++++++++++--- 6 files changed, 191 insertions(+), 11 deletions(-) diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index 678706dc94f..987bcb0938a 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,3 +1,23 @@ +2019-09-04 Mike Crowe + + PR libstdc++/41861 + * acinclude.m4 (GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT): Check for new + pthread_cond_clockwait function. + * configure.ac: Use GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT. + * configure: Regenerate. + * config.h.in: Regenerate. + * include/std/condition_variable: (condition_variable): Rename + __steady_clock_t typedef and add system_clock. Change __clock_t to be + a typedef for the preferred clock to convert arbitrary other clocks to. + [_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT] (wait_until): Add a steady_clock + overload. + (wait_until): Change __clock_t overload to use system_clock. + [_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT] (__wait_until_impl): Add + steady_clock overload that calls pthread_cond_clockwait. + (__wait_until_impl): Change __clock_t overload to use system_clock. + (condition_variable_any) [_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT]: Use + steady_clock for __clock_t if pthread_cond_clockwait is available. + 2019-09-04 Mike Crowe * testsuite/30_threads/condition_variable/members/2.cc (test01): diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4 index 727d6ce4239..bc9095f4799 100644 --- a/libstdc++-v3/acinclude.m4 +++ b/libstdc++-v3/acinclude.m4 @@ -4193,6 +4193,37 @@ AC_DEFUN([GLIBCXX_CHECK_PTHREADS_NUM_PROCESSORS_NP], [ AC_LANG_RESTORE ]) +dnl +dnl Check whether pthread_cond_clockwait is available in 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_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 $glibcxx_cv_PTHREAD_COND_CLOCKWAIT = yes; then + AC_DEFINE(_GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT, 1, [Define if pthread_cond_clockwait is available in .]) + fi + AC_MSG_RESULT($glibcxx_cv_PTHREAD_COND_CLOCKWAIT) + + CXXFLAGS="$ac_save_CXXFLAGS" + LIBS="$ac_save_LIBS" + AC_LANG_RESTORE +]) + dnl dnl Check whether sysctl is available in , and define _GLIBCXX_USE_SYSCTL_HW_NCPU. dnl diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in index 99286e67a27..3d13402f923 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 . */ #undef _GLIBCXX_USE_PTHREADS_NUM_PROCESSORS_NP +/* Define if pthread_cond_clockwait is available in . */ +#undef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT + /* Define if POSIX read/write locks are available in . */ #undef _GLIBCXX_USE_PTHREAD_RWLOCK_T diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure index e3ad6129c0a..f2f5098df91 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 ${glibcxx_cv_PTHREAD_COND_CLOCKWAIT+:} false; then : + $as_echo_n "(cached) " >&6 +else + + if test x$gcc_no_link = xyes; then + cat confdefs.h - <<_ACEOF >conftest.$ac_ext +/* end confdefs.h. */ +#include +int +main () +{ +pthread_mutex_t mutex; pthread_cond_t cond; struct timespec ts; int n = pthread_cond_clockwait(&cond, &mutex, 0, &ts); + ; + return 0; +} +_ACEOF +if ac_fn_cxx_try_compile "$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.$ac_ext +/* end confdefs.h. */ +#include +int +main () +{ +pthread_mutex_t mutex; pthread_cond_t cond; struct timespec ts; int n = pthread_cond_clockwait(&cond, &mutex, 0, &ts); + ; + return 0; +} +_ACEOF +if ac_fn_cxx_try_link "$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 80d8202c337..ad4ae0c3b7d 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 a83996aca3d..cc96661e94c 100644 --- a/libstdc++-v3/include/std/condition_variable +++ b/libstdc++-v3/include/std/condition_variable @@ -65,8 +65,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION /// condition_variable class condition_variable { - typedef chrono::system_clock __clock_t; - typedef chrono::steady_clock __steady_clock_t; + using steady_clock = chrono::steady_clock; + using system_clock = chrono::system_clock; +#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT + using __clock_t = steady_clock; +#else + using __clock_t = system_clock; +#endif typedef __gthread_cond_t __native_type; #ifdef __GTHREAD_COND_INIT @@ -101,10 +106,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION wait(__lock); } +#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT + template + cv_status + wait_until(unique_lock& __lock, + const chrono::time_point& __atime) + { return __wait_until_impl(__lock, __atime); } +#endif + template cv_status wait_until(unique_lock& __lock, - const chrono::time_point<__clock_t, _Duration>& __atime) + const chrono::time_point& __atime) { return __wait_until_impl(__lock, __atime); } template @@ -112,7 +125,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION wait_until(unique_lock& __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 auto __delta = __atime - __c_entry; @@ -145,11 +157,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION wait_for(unique_lock& __lock, const chrono::duration<_Rep, _Period>& __rtime) { - using __dur = typename __steady_clock_t::duration; + using __dur = typename steady_clock::duration; auto __reltime = chrono::duration_cast<__dur>(__rtime); if (__reltime < __rtime) ++__reltime; - return wait_until(__lock, __steady_clock_t::now() + __reltime); + return wait_until(__lock, steady_clock::now() + __reltime); } template @@ -158,11 +170,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION const chrono::duration<_Rep, _Period>& __rtime, _Predicate __p) { - using __dur = typename __steady_clock_t::duration; + using __dur = typename steady_clock::duration; auto __reltime = chrono::duration_cast<__dur>(__rtime); if (__reltime < __rtime) ++__reltime; - return wait_until(__lock, __steady_clock_t::now() + __reltime, + return wait_until(__lock, steady_clock::now() + __reltime, std::move(__p)); } @@ -171,10 +183,34 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION { return &_M_cond; } private: +#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT + template + cv_status + __wait_until_impl(unique_lock& __lock, + const chrono::time_point& __atime) + { + auto __s = chrono::time_point_cast(__atime); + auto __ns = chrono::duration_cast(__atime - __s); + + __gthread_time_t __ts = + { + static_cast(__s.time_since_epoch().count()), + static_cast(__ns.count()) + }; + + pthread_cond_clockwait(&_M_cond, __lock.mutex()->native_handle(), + CLOCK_MONOTONIC, + &__ts); + + return (steady_clock::now() < __atime + ? cv_status::no_timeout : cv_status::timeout); + } +#endif + template cv_status __wait_until_impl(unique_lock& __lock, - const chrono::time_point<__clock_t, _Dur>& __atime) + const chrono::time_point& __atime) { auto __s = chrono::time_point_cast(__atime); auto __ns = chrono::duration_cast(__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::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 { - typedef chrono::system_clock __clock_t; +#ifdef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT + using __clock_t = chrono::steady_clock; +#else + using __clock_t = chrono::system_clock; +#endif condition_variable _M_cond; shared_ptr _M_mutex; -- 2.30.2