QWaitCondition/Unix: do check for pthread_condattr_setclock()

Instead of guessing that Apple systems don't have it.

Because of this, we properly split the clockid_t constants in
qcore_unix_p.h between what the std::chrono::steady_clock uses and what
QWaitCondition will use. The difference is on Apple systems and on QNX.

Therefore, amends 5642b999754e75a9db3585b97ffbddac761f21b3.

Change-Id: Ibf5439b6cb4c332b0f24fffde43452e8ccd4e9c9
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>

src/corelib/configure.cmake

@@ -446,6 +446,20 @@ int main()
 }
 ")
 
+# pthread_condattr_setclock
+qt_config_compile_test(pthread_condattr_setclock
+    LABEL "pthread_condattr_setclock()"
+    LIBRARIES Threads::Threads
+    CODE
+"#include <pthread.h>
+#include <time.h>
+int main()
+{
+    pthread_condattr_t condattr;
+    return pthread_condattr_setclock(&condattr, CLOCK_REALTIME);
+}
+")
+
 # pthread_timedjoin
 qt_config_compile_test(pthread_timedjoin
     LABEL "pthread_timedjoin()"
@@ -730,6 +744,11 @@ qt_feature("pthread_clockjoin" PRIVATE
     AUTODETECT UNIX
     CONDITION UNIX AND QT_FEATURE_thread AND TEST_pthread_clockjoin
 )
+qt_feature("pthread_condattr_setclock" PRIVATE
+    LABEL "pthread_condattr_setclock() function"
+    AUTODETECT UNIX
+    CONDITION UNIX AND QT_FEATURE_thread AND TEST_pthread_condattr_setclock
+)
 qt_feature("pthread_timedjoin" PRIVATE
     LABEL "pthread_timedjoin() function"
     AUTODETECT UNIX

src/corelib/kernel/qcore_unix_p.h

@@ -75,14 +75,12 @@ static inline constexpr clockid_t SteadyClockClockId =
 #elif defined(__GLIBCXX__) && !defined(_GLIBCXX_USE_CLOCK_MONOTONIC)
         // libstdc++ falling back to system_clock
         CLOCK_REALTIME
-#elif defined(Q_OS_DARWIN)
+#elif defined(_LIBCPP_VERSION) && defined(Q_OS_DARWIN)
-        // Darwin lacks pthread_condattr_setclock()
+        // on Apple systems, libc++ uses CLOCK_MONOTONIC_RAW since LLVM 11
-        CLOCK_REALTIME
+        // https://github.com/llvm/llvm-project/blob/llvmorg-11.0.0/libcxx/src/chrono.cpp#L117-L129
-#elif defined(Q_OS_QNX)
+        CLOCK_MONOTONIC_RAW
-        // unknown why
-        CLOCK_REALTIME
 #elif defined(__GLIBCXX__) || defined(_LIBCPP_VERSION)
-        // both libstdc++ and libc++ do use CLOCK_MONOTONIC
+        // both libstdc++ and libc++ otherwise use CLOCK_MONOTONIC
         CLOCK_MONOTONIC
 #else
 #  warning "Unknown C++ Standard Library implementation - code may be sub-optimal"
@@ -90,6 +88,21 @@ static inline constexpr clockid_t SteadyClockClockId =
 #endif
         ;
 
+static inline constexpr clockid_t QWaitConditionClockId =
+#if !QT_CONFIG(thread)
+        // bootstrap mode, there are no wait conditions
+        CLOCK_REALTIME
+#elif !QT_CONFIG(pthread_condattr_setclock)
+        // OSes that lack pthread_condattr_setclock() (e.g., Darwin)
+        CLOCK_REALTIME
+#elif defined(Q_OS_QNX)
+        // unknown why use of the monotonic clock causes failures
+        CLOCK_REALTIME
+#else
+        SteadyClockClockId;
+#endif
+        ;
+
 static constexpr auto OneSecAsNsecs = std::chrono::nanoseconds(std::chrono::seconds{ 1 }).count();
 
 inline timespec durationToTimespec(std::chrono::nanoseconds timeout) noexcept
@@ -205,13 +218,14 @@ inline timespec qAbsTimespec(timespec ts)
     return normalizedTimespec(ts);
 }
 
+template <clockid_t ClockId = SteadyClockClockId>
 inline timespec deadlineToAbstime(QDeadlineTimer deadline)
 {
     using namespace std::chrono;
     using Clock =
-        std::conditional_t<SteadyClockClockId == CLOCK_REALTIME, system_clock, steady_clock>;
+        std::conditional_t<ClockId == CLOCK_REALTIME, system_clock, steady_clock>;
     auto timePoint = deadline.deadline<Clock>();
-    if (timePoint < Clock::time_point{})
+    if (timePoint < typename Clock::time_point{})
         return {};
     return durationToTimespec(timePoint.time_since_epoch());
 }

src/corelib/thread/qthread_unix.cpp

@@ -95,7 +95,7 @@ enum { ThreadPriorityResetFlag = 0x80000000 };
 //
 // To support this scenario, we start the thread in detached state.
 static constexpr bool UsingPThreadTimedJoin = QT_CONFIG(pthread_clockjoin)
-        || (QT_CONFIG(pthread_timedjoin) && SteadyClockClockId == CLOCK_REALTIME);
+        || (QT_CONFIG(pthread_timedjoin) && QWaitConditionClockId == CLOCK_REALTIME);
 #if !QT_CONFIG(pthread_clockjoin)
 int pthread_clockjoin_np(...) { return ENOSYS; }    // pretend
 #endif

src/corelib/thread/qwaitcondition_unix.cpp

@@ -30,14 +30,14 @@ static void qt_initialize_pthread_cond(pthread_cond_t *cond, const char *where)
 {
     pthread_condattr_t *attrp = nullptr;
 
-#if defined(CLOCK_MONOTONIC) && !defined(Q_OS_DARWIN)
+#if QT_CONFIG(pthread_condattr_setclock)
     pthread_condattr_t condattr;
     attrp = &condattr;
 
     pthread_condattr_init(&condattr);
     auto destroy = qScopeGuard([&] { pthread_condattr_destroy(&condattr); });
-    if (SteadyClockClockId != CLOCK_REALTIME)
+    if (QWaitConditionClockId != CLOCK_REALTIME)
-        pthread_condattr_setclock(&condattr, SteadyClockClockId);
+        pthread_condattr_setclock(&condattr, QWaitConditionClockId);
 #endif
 
     qt_report_pthread_error(pthread_cond_init(cond, attrp), where, "cv init");
@@ -53,7 +53,7 @@ public:
 
     int wait_relative(QDeadlineTimer deadline)
     {
-        timespec ti = deadlineToAbstime(deadline);
+        timespec ti = deadlineToAbstime<QWaitConditionClockId>(deadline);
         return pthread_cond_timedwait(&cond, &mutex, &ti);
     }