[09/11] libstdc++ shared_mutex: Add full steady_clock support to shared_timed_mutex

Message ID 7df79aa7977218282444035759bef1ffa3e608a6.1569660153.git-series.mac@mcrowe.com
State Superseded
Headers show
Series
  • timed_mutex, shared_timed_mutex: Add full steady clock support
Related show

Commit Message

Mike Crowe Sept. 28, 2019, 8:44 a.m.
The pthread_rwlock_clockrdlock and pthread_rwlock_clockwrlock functions
were added to glibc in v2.30. They have also been added to Android
Bionic. If these functions are available in the C library then they can be
used to implement shared_timed_mutex::try_lock_until,
shared_timed_mutex::try_lock_for, shared_timed_mutex::try_lock_shared_until
and shared_timed_mutex::try_lock_shared_for so that they are no longer
unaffected by the system clock being warped. (This is the shared_mutex
equivalent of PR libstdc++/78237 for mutex.)

If the new functions are 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. It's not possible to have
_GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK defined without
_GLIBCXX_USE_PTHREAD_RWLOCK_T, so the requirement that the clock be the
same as condition_variable is maintained. Calls explicitly using
system_clock (aka high_resolution_clock) continue to use CLOCK_REALTIME via
the old pthread_rwlock_timedrdlock and pthread_rwlock_timedwrlock
functions.

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

	* libstdc++-v3/acinclude.m4: Define
	GLIBCXX_CHECK_PTHREAD_RWLOCK_CLOCKLOCK to check for the presence of
	both pthread_rwlock_clockrdlock and pthread_rwlock_clockwrlock.

	* config.h.in: Add _GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK define.

	* configure.ac: Call GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK.

	* configure: Add generated part to detect
	pthread_rwlock_clockrdlock and pthread_rwlock_clockwrlock
	functions.

	* include/std/shared_mutex (shared_timed_mutex): Define __clock_t
	as the best clock to use for relative waits. (try_lock_until): Use
	existing try_lock_until implementation for system_clock (which
	matches __clock_t when _GLIBCCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK is
	not defined). Add new overload for steady_clock that uses
	pthread_rwlock_clockwrlock if it is available. Simplify overload
	for non-standard clock to just call try_lock_for with a relative
	timeout. (try_lock_shared_until): Likewise.
---
 libstdc++-v3/acinclude.m4             | 33 +++++++++++-
 libstdc++-v3/config.h.in              |  4 +-
 libstdc++-v3/configure                | 88 ++++++++++++++++++++++++++++-
 libstdc++-v3/configure.ac             |  3 +-
 libstdc++-v3/include/std/shared_mutex | 87 ++++++++++++++++++++++------
 5 files changed, 198 insertions(+), 17 deletions(-)

-- 
git-series 0.9.1

Patch

diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 9ecfa96..d860dbe 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -4259,6 +4259,39 @@  AC_DEFUN([GLIBCXX_CHECK_PTHREAD_MUTEX_CLOCKLOCK], [
 ])
 
 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_RWLOCK_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_rwlock_clockrdlock, pthread_wlock_clockwrlock])
+  AC_CACHE_VAL(glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK, [
+    GCC_TRY_COMPILE_OR_LINK(
+      [#include <pthread.h>],
+      [pthread_rwlock_t rwl; struct timespec ts;]
+      [int n = pthread_rwlock_clockrdlock(&rwl, CLOCK_REALTIME, &ts);]
+      [int m = pthread_rwlock_clockwrlock(&rwl, CLOCK_REALTIME, &ts);],
+      [glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK=yes],
+      [glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK=no])
+  ])
+  if test $glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK = yes; then
+    AC_DEFINE(_GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK, 1, [Define if pthread_rwlock_clockrdlock and pthread_rwlock_clockwrlock are available in <pthread.h>.])
+  fi
+  AC_MSG_RESULT($glibcxx_cv_PTHREAD_RWLOCK_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 9670176..6935797 100644
--- a/libstdc++-v3/config.h.in
+++ b/libstdc++-v3/config.h.in
@@ -997,6 +997,10 @@ 
 /* Define if pthread_mutex_clocklock is available in <pthread.h>. */
 #undef _GLIBCXX_USE_PTHREAD_MUTEX_CLOCKLOCK
 
+/* Define if pthread_rwlock_clockrdlock and pthread_rwlock_clockwrlock are
+   available in <pthread.h>. */
+#undef _GLIBCXX_USE_PTHREAD_RWLOCK_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 41df34c..0265c1a 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -21760,6 +21760,94 @@  ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
+# For pthread_rwlock_clockrdlock and pthread_rwlock_clockwrlock
+
+
+
+  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_rwlock_clockrdlock, pthread_wlock_clockwrlock" >&5
+$as_echo_n "checking for pthread_rwlock_clockrdlock, pthread_wlock_clockwrlock... " >&6; }
+  if ${glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+
+    if test x$gcc_no_link = xyes; then
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <pthread.h>
+int
+main ()
+{
+pthread_rwlock_t rwl; struct timespec ts;
+      int n = pthread_rwlock_clockrdlock(&rwl, CLOCK_REALTIME, &ts);
+      int m = pthread_rwlock_clockwrlock(&rwl, CLOCK_REALTIME, &ts);
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK=yes
+else
+  glibcxx_cv_PTHREAD_RWLOCK_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.$ac_ext
+/* end confdefs.h.  */
+#include <pthread.h>
+int
+main ()
+{
+pthread_rwlock_t rwl; struct timespec ts;
+      int n = pthread_rwlock_clockrdlock(&rwl, CLOCK_REALTIME, &ts);
+      int m = pthread_rwlock_clockwrlock(&rwl, CLOCK_REALTIME, &ts);
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_link "$LINENO"; then :
+  glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK=yes
+else
+  glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+fi
+
+fi
+
+  if test $glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK = yes; then
+
+$as_echo "#define _GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK 1" >>confdefs.h
+
+  fi
+  { $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK" >&5
+$as_echo "$glibcxx_cv_PTHREAD_RWLOCK_CLOCKLOCK" >&6; }
+
+  CXXFLAGS="$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 35d346f..f5d2768 100644
--- a/libstdc++-v3/configure.ac
+++ b/libstdc++-v3/configure.ac
@@ -226,6 +226,9 @@  GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT
 # For pthread_mutex_clocklock
 GLIBCXX_CHECK_PTHREAD_MUTEX_CLOCKLOCK
 
+# For pthread_rwlock_clockrdlock and pthread_rwlock_clockwrlock
+GLIBCXX_CHECK_PTHREAD_RWLOCK_CLOCKLOCK
+
 AC_LC_MESSAGES
 
 # For hardware_concurrency
diff --git a/libstdc++-v3/include/std/shared_mutex b/libstdc++-v3/include/std/shared_mutex
index ffd93fb..b637bdc 100644
--- a/libstdc++-v3/include/std/shared_mutex
+++ b/libstdc++-v3/include/std/shared_mutex
@@ -450,7 +450,11 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
     using _Base = __shared_timed_mutex_base;
 
     // Must use the same clock as condition_variable for __shared_mutex_cv.
-    typedef chrono::system_clock	__clock_t;
+#ifdef _GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK
+    using __clock_t = chrono::steady_clock;
+#else
+    using __clock_t = chrono::system_clock;
+#endif
 
   public:
     shared_timed_mutex() = default;
@@ -491,7 +495,8 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     template<typename _Duration>
       bool
-      try_lock_until(const chrono::time_point<__clock_t, _Duration>& __atime)
+      try_lock_until(const chrono::time_point<chrono::system_clock,
+                     _Duration>& __atime)
       {
 	auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
 	auto __ns = chrono::duration_cast<chrono::nanoseconds>(__atime - __s);
@@ -512,23 +517,47 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return true;
       }
 
+#ifdef _GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK
+    template<typename _Duration>
+      bool
+      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())
+	  };
+
+	int __ret = pthread_rwlock_clockwrlock(&_M_rwlock, CLOCK_MONOTONIC,
+                                             &__ts);
+	// On self-deadlock, we just fail to acquire the lock.  Technically,
+	// the program violated the precondition.
+	if (__ret == ETIMEDOUT || __ret == EDEADLK)
+	  return false;
+	// Errors not handled: EINVAL
+	__glibcxx_assert(__ret == 0);
+	return true;
+      }
+#endif
+
     template<typename _Clock, typename _Duration>
       bool
-      try_lock_until(const chrono::time_point<_Clock, _Duration>& __abs_time)
+      try_lock_until(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 = __abs_time - __c_entry;
-	const auto __s_atime = __s_entry + __delta;
-	return try_lock_until(__s_atime);
+        typename _Clock::time_point __now = _Clock::now();
+        auto __rtime = __atime - __now;
+        return try_lock_for(__rtime);
       }
 
     // Shared ownership
 
     template<typename _Duration>
       bool
-      try_lock_shared_until(const chrono::time_point<__clock_t,
+      try_lock_shared_until(const chrono::time_point<chrono::system_clock,
 			    _Duration>& __atime)
       {
 	auto __s = chrono::time_point_cast<chrono::seconds>(__atime);
@@ -564,17 +593,41 @@  _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	return true;
       }
 
+#ifdef _GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK
+    template<typename _Duration>
+      bool
+      try_lock_shared_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())
+	  };
+
+	int __ret = pthread_rwlock_clockrdlock(&_M_rwlock, CLOCK_MONOTONIC,
+                                             &__ts);
+	// On self-deadlock, we just fail to acquire the lock.  Technically,
+	// the program violated the precondition.
+	if (__ret == ETIMEDOUT || __ret == EDEADLK)
+	  return false;
+	// Errors not handled: EINVAL
+	__glibcxx_assert(__ret == 0);
+	return true;
+      }
+#endif
+
     template<typename _Clock, typename _Duration>
       bool
       try_lock_shared_until(const chrono::time_point<_Clock,
-						     _Duration>& __abs_time)
+						     _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 = __abs_time - __c_entry;
-	const auto __s_atime = __s_entry + __delta;
-	return try_lock_shared_until(__s_atime);
+        typename _Clock::time_point __now = _Clock::now();
+        auto __rtime = __atime - __now;
+        return try_lock_shared_for(__rtime);
       }
 
 #else // ! (_GLIBCXX_USE_PTHREAD_RWLOCK_T && _GTHREAD_USE_MUTEX_TIMEDLOCK)