@@ -3652,6 +3652,37 @@ AC_DEFUN([GLIBCXX_CHECK_PTHREADS_NUM_PROCESSORS_NP], [
])
dnl
+dnl Check whether pthread_cond_timedwaitonclock_np is available in <pthread.h> for std::condition_variable to use,
+dnl and define _GLIBCXX_USE_PTHREAD_COND_TIMEDWAITONCLOCK_NP.
+dnl
+AC_DEFUN([GLIBCXX_CHECK_PTHREAD_COND_TIMEDWAITONCLOCK_NP], [
+
+ 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_timedwaitonclock_np])
+ AC_CACHE_VAL(glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP, [
+ GCC_TRY_COMPILE_OR_LINK(
+ [#include <pthread.h>],
+ [pthread_mutex_t mutex; pthread_cond_t cond; struct timespec ts; int n = pthread_cond_timedwaitonclock_np(&cond, &mutex, 0, &ts);],
+ [glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP=yes],
+ [glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP=no])
+ ])
+ if test $glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP = yes; then
+ AC_DEFINE(_GLIBCXX_USE_PTHREAD_COND_TIMEDWAITONCLOCK_NP, 1, [Define if pthread_cond_timedwaitonclock_np is available in <pthread.h>.])
+ fi
+ AC_MSG_RESULT($glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP)
+
+ 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], [
@@ -869,6 +869,9 @@
/* Define if pthreads_num_processors_np is available in <pthread.h>. */
#undef _GLIBCXX_USE_PTHREADS_NUM_PROCESSORS_NP
+/* Define if pthread_cond_timedwaitonclock_np is available in <pthread.h>. */
+#undef _GLIBCXX_USE_PTHREAD_COND_TIMEDWAITONCLOCK_NP
+
/* Define if POSIX read/write locks are available in <gthr.h>. */
#undef _GLIBCXX_USE_PTHREAD_RWLOCK_T
@@ -20220,6 +20220,89 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
+# For pthread_cond_timedwaitonclock_np
+
+
+
+ ac_ext=cpp
+ac_cpp='$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_timedwaitonclock_np" >&5
+$as_echo_n "checking for pthread_cond_timedwaitonclock_np... " >&6; }
+ if test "${glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP+set}" = set; then :
+ $as_echo_n "(cached) " >&6
+else
+
+ if test x$gcc_no_link = xyes; then
+ cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h. */
+#include <pthread.h>
+int
+main ()
+{
+pthread_mutex_t mutex; pthread_cond_t cond; struct timespec ts; int n = pthread_cond_timedwaitonclock_np(&cond, &mutex, 0, &ts);
+ ;
+ return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+ glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP=yes
+else
+ glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP=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.$ac_ext
+/* end confdefs.h. */
+#include <pthread.h>
+int
+main ()
+{
+pthread_mutex_t mutex; pthread_cond_t cond; struct timespec ts; int n = pthread_cond_timedwaitonclock_np(&cond, &mutex, 0, &ts);
+ ;
+ return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_link "$LINENO"; then :
+ glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP=yes
+else
+ glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+ conftest$ac_exeext conftest.$ac_ext
+fi
+
+fi
+
+ if test $glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP = yes; then
+
+$as_echo "#define _GLIBCXX_USE_PTHREAD_COND_TIMEDWAITONCLOCK_NP 1" >>confdefs.h
+
+ fi
+ { $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP" >&5
+$as_echo "$glibcxx_cv_PTHREAD_COND_TIMEDWAITONCLOCK_NP" >&6; }
+
+ CXXFLAGS="$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" = x""yes; then :
@@ -218,6 +218,9 @@ GLIBCXX_ENABLE_LIBSTDCXX_TIME
# Check for tmpnam which is obsolescent in POSIX.1-2008
GLIBCXX_CHECK_TMPNAM
+# For pthread_cond_timedwaitonclock_np
+GLIBCXX_CHECK_PTHREAD_COND_TIMEDWAITONCLOCK_NP
+
AC_LC_MESSAGES
# For hardware_concurrency
@@ -35,6 +35,7 @@
# include <bits/c++0x_warning.h>
#else
+#include <bits/c++config.h>
#include <chrono>
#include <mutex>
#include <ext/concurrence.h>
@@ -63,7 +64,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/// condition_variable
class condition_variable
{
- typedef chrono::system_clock __clock_t;
+#if defined(_GLIBCXX_USE_PTHREAD_COND_TIMEDWAITONCLOCK_NP)
+ typedef chrono::steady_clock __steady_clock_t;
+ 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
@@ -98,10 +105,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
wait(__lock);
}
+#if defined(_GLIBCXX_USE_PTHREAD_COND_TIMEDWAITONCLOCK_NP)
template<typename _Duration>
cv_status
wait_until(unique_lock<mutex>& __lock,
- const chrono::time_point<__clock_t, _Duration>& __atime)
+ 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<__system_clock_t, _Duration>& __atime)
{ return __wait_until_impl(__lock, __atime); }
template<typename _Clock, typename _Duration>
@@ -109,9 +124,8 @@ _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;
@@ -134,24 +148,47 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
cv_status
wait_for(unique_lock<mutex>& __lock,
const chrono::duration<_Rep, _Period>& __rtime)
- { return wait_until(__lock, __clock_t::now() + __rtime); }
+ { return wait_until(__lock, __best_clock_t::now() + __rtime); }
template<typename _Rep, typename _Period, typename _Predicate>
bool
wait_for(unique_lock<mutex>& __lock,
const chrono::duration<_Rep, _Period>& __rtime,
_Predicate __p)
- { return wait_until(__lock, __clock_t::now() + __rtime, std::move(__p)); }
+ { return wait_until(__lock, __best_clock_t::now() + __rtime, std::move(__p)); }
native_handle_type
native_handle()
{ return &_M_cond; }
private:
+#if defined(_GLIBCXX_USE_PTHREAD_COND_TIMEDWAITONCLOCK_NP)
+ 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_timedwaitonclock_np(&_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);
@@ -165,7 +202,7 @@ _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);
}
};
@@ -185,7 +222,11 @@ _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_TIMEDWAITONCLOCK_NP)
+ typedef chrono::steady_clock __clock_t;
+#else
typedef chrono::system_clock __clock_t;
+#endif
condition_variable _M_cond;
shared_ptr<mutex> _M_mutex;
@@ -27,6 +27,7 @@
#include <system_error>
#include <testsuite_hooks.h>
+template <typename ClockType>
void test01()
{
bool test __attribute__((unused)) = true;
@@ -38,10 +39,10 @@ void test01()
std::mutex m;
std::unique_lock<std::mutex> l(m);
- auto then = std::chrono::steady_clock::now();
+ auto then = ClockType::now();
std::cv_status result = c1.wait_until(l, then + ms);
VERIFY( result == std::cv_status::timeout );
- VERIFY( (std::chrono::steady_clock::now() - then) >= ms );
+ VERIFY( (ClockType::now() - then) >= ms );
VERIFY( l.owns_lock() );
}
catch (const std::system_error& e)
@@ -54,8 +55,28 @@ void test01()
}
}
+/* User defined clock that ticks in two-thousandths of a second
+ forty-two minutes ahead of steady_clock. */
+struct user_defined_clock
+{
+ typedef std::chrono::steady_clock::rep rep;
+ typedef std::ratio<1,2000> period;
+ typedef std::chrono::duration<rep, period> duration;
+ typedef std::chrono::time_point<user_defined_clock> time_point;
+
+ const bool is_steady = true;
+
+ static time_point now() noexcept
+ {
+ using namespace std::chrono;
+ return time_point(duration_cast<duration>(steady_clock::now().time_since_epoch()) + minutes(42));
+ }
+};
+
int main()
{
- test01();
+ test01<std::chrono::steady_clock>();
+ test01<std::chrono::system_clock>();
+ test01<user_defined_clock>();
return 0;
}
@@ -52,6 +52,7 @@ struct Mutex
};
+template <typename ClockType>
void test01()
{
bool test __attribute__((unused)) = true;
@@ -63,10 +64,10 @@ void test01()
Mutex m;
m.lock();
- auto then = std::chrono::steady_clock::now();
+ auto then = ClockType::now();
std::cv_status result = c1.wait_until(m, then + ms);
VERIFY( result == std::cv_status::timeout );
- VERIFY( (std::chrono::steady_clock::now() - then) >= ms );
+ VERIFY( (ClockType::now() - then) >= ms );
VERIFY( m.locked );
}
catch (const std::system_error& e)
@@ -79,8 +80,28 @@ void test01()
}
}
+/* User defined clock that ticks in two-thousandths of a second
+ forty-two minutes ahead of steady_clock. */
+struct user_defined_clock
+{
+ typedef std::chrono::steady_clock::rep rep;
+ typedef std::ratio<1,2000> period;
+ typedef std::chrono::duration<rep, period> duration;
+ typedef std::chrono::time_point<user_defined_clock> time_point;
+
+ const bool is_steady = true;
+
+ static time_point now() noexcept
+ {
+ using namespace std::chrono;
+ return time_point(duration_cast<duration>(steady_clock::now().time_since_epoch()) + minutes(42));
+ }
+};
+
int main()
{
- test01();
+ test01<std::chrono::steady_clock>();
+ test01<std::chrono::system_clock>();
+ test01<user_defined_clock>();
return 0;
}
If pthread_cond_timedwaitonclock_np is available in the C library it can be used it to fix part of 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 changed at an inopportune moment. If pthread_cond_timedwaitonclock_np 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. If pthread_cond_timedwaitonclock_np is not available then std::chrono::system_clock is deemed to be the "best" clock available which means that the previous suboptimal behaviour remains. (I have a patch that adds pthread_cond_timedwaitonclock_np to glibc ready to submit but I wanted to get feedback on this part of the change before submitting the glibc patch. See https://gitlab.com/mikecrowe/glibc-monotonic .) Signed-off-by: Mike Crowe <mac@mcrowe.com> --- 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 | 57 ++++++++++++--- .../30_threads/condition_variable/members/2.cc | 27 ++++++- .../30_threads/condition_variable_any/members/2.cc | 27 ++++++- 7 files changed, 217 insertions(+), 14 deletions(-)