libstdc++: Add full steady_clock support to shared_timed_mutex

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.

Additionally, the user-defined clock used with
shared_timed_mutex::try_lock_for and shared_mutex::try_lock_shared_for
may have higher precision than __clock_t. We may need to round the
duration up to ensure that the timeout is long enough. (See
__timed_mutex_impl::_M_try_lock_for)

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

	Add full steady_clock support to shared_timed_mutex
	* acinclude.m4 (GLIBCXX_CHECK_PTHREAD_RWLOCK_CLOCKLOCK): Define
	to check for the presence of both pthread_rwlock_clockrdlock and
	pthread_rwlock_clockwrlock.
	* config.h.in: Regenerate.
	* configure.ac: Call GLIBCXX_USE_PTHREAD_RWLOCK_CLOCKLOCK.
	* configure: Regenerate.
	* include/std/shared_mutex (shared_timed_mutex): Define __clock_t as
	the best clock to use for relative waits.
	(shared_timed_mutex::try_lock_for) Round up wait duration if necessary.
	(shared_timed_mutex::try_lock_shared_for): Likewise.
	(shared_timed_mutex::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.
	(shared_timed_mutex::try_lock_shared_until): Likewise.

From-SVN: r278903

1 files changed, 87 insertions, 0 deletions

diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index a439bb86e6e..b7242157107 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -21963,6 +21963,93 @@ 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 :