If __gthread_cond_timedwaitonclock is available 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 __gthread_cond_timedwaitonclock 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 that aren't choosing to use std::chrono::system_clock.
Calls explicitly using std::chrono::system_clock continue to use
CLOCK_REALTIME.
If __gthread_cond_timedwaitonclock is not available then
std::chrono::system_clock is deemed to be the "best" clock available
which means that the previous suboptimal behaviour remains.
Signed-off-by: Mike Crowe <m...@mcrowe.com>
---
libstdc++-v3/include/std/condition_variable | 56 ++++++++++++++++++----
.../30_threads/condition_variable/members/2.cc | 8 ++--
2 files changed, 53 insertions(+), 11 deletions(-)
diff --git a/libstdc++-v3/include/std/condition_variable
b/libstdc++-v3/include/std/condition_variable
index f7da017..625ecfe 100644
--- a/libstdc++-v3/include/std/condition_variable
+++ b/libstdc++-v3/include/std/condition_variable
@@ -63,7 +63,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/// condition_variable
class condition_variable
{
- typedef chrono::system_clock __clock_t;
+#ifdef _GTHREAD_USE_COND_TIMEDWAITONCLOCK
+ 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 +104,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
wait(__lock);
}
+#ifdef _GTHREAD_USE_COND_TIMEDWAITONCLOCK
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 +123,8 @@ _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 +147,47 @@ _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:
+#ifdef _GTHREAD_USE_COND_TIMEDWAITONCLOCK
+ 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())
+ };
+
+ __gthread_cond_timedwaitonclock(&_M_cond,
__lock.mutex()->native_handle(),
+ __GTHREAD_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 +201,7 @@ _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 +221,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// Like above, but mutex is not required to have try_lock.
class condition_variable_any
{
+#ifdef _GTHREAD_USE_COND_TIMEDWAITONCLOCK
+ typedef chrono::steady_clock __clock_t;
+#else
typedef chrono::system_clock __clock_t;
+#endif
condition_variable _M_cond;
shared_ptr<mutex> _M_mutex;
diff --git a/libstdc++-v3/testsuite/30_threads/condition_variable/members/2.cc
b/libstdc++-v3/testsuite/30_threads/condition_variable/members/2.cc
index 04945f1..79d511e 100644
--- a/libstdc++-v3/testsuite/30_threads/condition_variable/members/2.cc
+++ b/libstdc++-v3/testsuite/30_threads/condition_variable/members/2.cc
@@ -27,6 +27,7 @@
#include <system_error>
#include <testsuite_hooks.h>
+template <typename CLOCK>
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 = CLOCK::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( (CLOCK::now() - then) >= ms );
VERIFY( l.owns_lock() );
}
catch (const std::system_error& e)
@@ -56,6 +57,7 @@ void test01()
int main()
{
- test01();
+ test01<std::chrono::steady_clock>();
+ test01<std::chrono::system_clock>();
return 0;
}
--
2.1.4
