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

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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
This commit is contained in:
Mike Crowe 2019-12-02 16:23:01 +00:00 committed by Jonathan Wakely
parent 49638674a4
commit 3b2fb54353
6 changed files with 179 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
libstdc++-v3/ChangeLog
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@ -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

31
libstdc++-v3/acinclude.m4
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@ -4227,6 +4227,37 @@ AC_DEFUN([GLIBCXX_CHECK_PTHREAD_COND_CLOCKWAIT], [
AC_LANG_RESTORE
])
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

3
libstdc++-v3/config.h.in
View File

@ -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

83
libstdc++-v3/configure vendored
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@ -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 :

3
libstdc++-v3/configure.ac
View File

@ -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

50
libstdc++-v3/include/std/mutex
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@ -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