libstdc++: PR 78237 Add full steady_clock support to timed_mutex

The pthread_mutex_clocklock 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++/78237 by supporting steady_clock properly with
timed_mutex.

This means that code using timed_mutex::try_lock_for or
timed_mutex::wait_until with 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_mutex_clocklock is available then steady_clock is deemed to
be the "best" clock available which means that it is used for the
relative try_lock_for calls and absolute try_lock_until calls using
steady_clock and user-defined clocks. Calls explicitly using
system_clock (aka high_resolution_clock) continue to use CLOCK_REALTIME
via __gthread_cond_timedwait.

If pthread_mutex_clocklock is not available then system_clock is deemed
to be the "best" clock available which means that the previous
suboptimal behaviour remains.

2019-12-02  Mike Crowe  <mac@mcrowe.com>

	PR libstdc++/78237 Add full steady_clock support to timed_mutex
	* acinclude.m4 (GLIBCXX_CHECK_PTHREAD_MUTEX_CLOCKLOCK): Define to
	detect presence of pthread_mutex_clocklock function.
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* configure.ac: Call GLIBCXX_CHECK_PTHREAD_MUTEX_CLOCKLOCK.
	* include/std/mutex (__timed_mutex_impl): Remove unnecessary __clock_t.
	(__timed_mutex_impl::_M_try_lock_for): Use best clock to turn relative
	timeout into absolute timeout.
	(__timed_mutex_impl::_M_try_lock_until): Keep existing implementation
	for system_clock. Add new implementation for steady_clock that calls
	_M_clocklock. Modify overload for user-defined clock to use a relative
	wait so that it automatically uses the best clock.
	[_GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK] (timed_mutex::_M_clocklock):
	New member function.
	(recursive_timed_mutex::_M_clocklock): Likewise.

From-SVN: r278901

6 files changed, 179 insertions, 8 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 24a4a35..d39a06f 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,22 @@
 2019-12-02  Mike Crowe  <mac@mcrowe.com>
 
+	PR libstdc++/78237 Add full steady_clock support to timed_mutex
+	* acinclude.m4 (GLIBCXX_CHECK_PTHREAD_MUTEX_CLOCKLOCK): Define to
+	detect presence of pthread_mutex_clocklock function.
+	* config.h.in: Regenerate.
+	* configure: Regenerate.
+	* configure.ac: Call GLIBCXX_CHECK_PTHREAD_MUTEX_CLOCKLOCK.
+	* include/std/mutex (__timed_mutex_impl): Remove unnecessary __clock_t.
+	(__timed_mutex_impl::_M_try_lock_for): Use best clock to turn relative
+	timeout into absolute timeout.
+	(__timed_mutex_impl::_M_try_lock_until): Keep existing implementation
+	for system_clock. Add new implementation for steady_clock that calls
+	_M_clocklock. Modify overload for user-defined clock to use a relative
+	wait so that it automatically uses the best clock.
+	[_GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK] (timed_mutex::_M_clocklock):
+	New member function.
+	(recursive_timed_mutex::_M_clocklock): Likewise.
+
 	* testsuite/30_threads/recursive_timed_mutex/try_lock_until/3.cc:
 	New test. Ensure that timed_mutex::try_lock_until actually times out
 	after the specified time when using both system_clock and
diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 73e07e5..7e685bb 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -4228,6 +4228,37 @@ AC_DEFUN([GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT], [
 ])
 
 dnl
+dnl Check whether pthread_mutex_clocklock is available in <pthread.h> for std::timed_mutex to use,
+dnl and define _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK.
+dnl
+AC_DEFUN([GLIBCXX_CHECK_PTHREAD_MUTEX_CLOCKLOCK], [
+
+  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_mutex_clocklock])
+  AC_CACHE_VAL(glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK, [
+    GCC_TRY_COMPILE_OR_LINK(
+      [#include <pthread.h>],
+      [pthread_mutex_t mutex; struct timespec ts; int n = pthread_mutex_clocklock(&mutex, CLOCK_REALTIME, &ts);],
+      [glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK=yes],
+      [glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK=no])
+  ])
+  if test $glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK = yes; then
+    AC_DEFINE(_GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK, 1, [Define if pthread_mutex_clocklock is available in <pthread.h>.])
+  fi
+  AC_MSG_RESULT($glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK)
+
+  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 32f7863..3d51534 100644
--- a/libstdc++-v3/config.h.in
+++ b/libstdc++-v3/config.h.in
@@ -1002,6 +1002,9 @@
 /* Define if pthread_cond_clockwait is available in <pthread.h>. */
 #undef _GLIBCXX_USE_PTHREAD_COND_CLOCKWAIT
 
+/* Define if pthread_mutex_clocklock is available in <pthread.h>. */
+#undef _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK
+
 /* 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 e1d24132..a439bb8 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -21880,6 +21880,89 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
+# For pthread_mutex_clocklock
+
+
+
+  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_mutex_clocklock" >&5
+$as_echo_n "checking for pthread_mutex_clocklock... " >&6; }
+  if ${glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+
+    if test x$gcc_no_link = xyes; then
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <pthread.h>
+int
+main ()
+{
+pthread_mutex_t mutex; struct timespec ts; int n = pthread_mutex_clocklock(&mutex, CLOCK_REALTIME, &ts);
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK=yes
+else
+  glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK=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.$ac_ext
+/* end confdefs.h.  */
+#include <pthread.h>
+int
+main ()
+{
+pthread_mutex_t mutex; struct timespec ts; int n = pthread_mutex_clocklock(&mutex, CLOCK_REALTIME, &ts);
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_link "$LINENO"; then :
+  glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK=yes
+else
+  glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+fi
+
+fi
+
+  if test $glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK = yes; then
+
+$as_echo "#define _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK 1" >>confdefs.h
+
+  fi
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK" >&5
+$as_echo "$glibcxx_cv_PTHREAD_MUTEX_CLOCKLOCK" >&6; }
+
+  CXXFLAGS="$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 154819a..c1ecc67 100644
--- a/libstdc++-v3/configure.ac
+++ b/libstdc++-v3/configure.ac
@@ -225,6 +225,9 @@ GLIBCXX_CHECK_TMPNAM
 # For pthread_cond_clockwait
 GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT
 
+# For pthread_mutex_clocklock
+GLIBCXX_CHECK_PTHREAD_MUTEX_CLOCKLOCK
+
 AC_LC_MESSAGES
 
 # For hardware_concurrency
diff --git a/libstdc++-v3/include/std/mutex b/libstdc++-v3/include/std/mutex
index 981b672..26ee084 100644
--- a/libstdc++-v3/include/std/mutex
+++ b/libstdc++-v3/include/std/mutex
@@ -134,22 +134,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     class __timed_mutex_impl
     {
     protected:
-      typedef chrono::high_resolution_clock 	__clock_t;
-
       template<typename _Rep, typename _Period>
 	bool
 	_M_try_lock_for(const chrono::duration<_Rep, _Period>& __rtime)
 	{
-	  using chrono::steady_clock;
-	  auto __rt = chrono::duration_cast<steady_clock::duration>(__rtime);
-	  if (ratio_greater<steady_clock::period, _Period>())
+#if _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK
+	  using __clock = chrono::steady_clock;
+#else
+	  using __clock = chrono::system_clock;
+#endif
+
+	  auto __rt = chrono::duration_cast<__clock::duration>(__rtime);
+	  if (ratio_greater<__clock::period, _Period>())
 	    ++__rt;
-	  return _M_try_lock_until(steady_clock::now() + __rt);
+	  return _M_try_lock_until(__clock::now() + __rt);
 	}
 
       template<typename _Duration>
 	bool
-	_M_try_lock_until(const chrono::time_point<__clock_t,
+	_M_try_lock_until(const chrono::time_point<chrono::system_clock,
 						   _Duration>& __atime)
 	{
 	  auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
@@ -163,12 +166,31 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  return static_cast<_Derived*>(this)->_M_timedlock(__ts);
 	}
 
+#ifdef _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK
+      template<typename _Duration>
+	bool
+	_M_try_lock_until(const chrono::time_point<chrono::steady_clock,
+						   _Duration>& __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())
+	  };
+
+	  return static_cast<_Derived*>(this)->_M_clocklock(CLOCK_MONOTONIC,
+							    __ts);
+	}
+#endif
+
       template<typename _Clock, typename _Duration>
 	bool
 	_M_try_lock_until(const chrono::time_point<_Clock, _Duration>& __atime)
 	{
 	  auto __rtime = __atime - _Clock::now();
-	  return _M_try_lock_until(__clock_t::now() + __rtime);
+	  return _M_try_lock_for(__rtime);
 	}
     };
 
@@ -229,6 +251,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       bool
       _M_timedlock(const __gthread_time_t& __ts)
       { return !__gthread_mutex_timedlock(&_M_mutex, &__ts); }
+
+#if _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK
+      bool
+      _M_clocklock(clockid_t clockid, const __gthread_time_t& __ts)
+      { return !pthread_mutex_clocklock(&_M_mutex, clockid, &__ts); }
+#endif
   };
 
   /// recursive_timed_mutex
@@ -289,6 +317,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       bool
       _M_timedlock(const __gthread_time_t& __ts)
       { return !__gthread_recursive_mutex_timedlock(&_M_mutex, &__ts); }
+
+#ifdef _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK
+      bool
+      _M_clocklock(clockid_t clockid, const __gthread_time_t& __ts)
+      { return !pthread_mutex_clocklock(&_M_mutex, clockid, &__ts); }
+#endif
   };
 
 #else // !_GTHREAD_USE_MUTEX_TIMEDLOCK