QSingleShotTimer: use nanoseconds precision

This is a step towards making QChronoTimer have nanoseconds precision.

Not changing QTimer::singleShot() methods to take nanoseconds; QTimer
uses milliseconds for the most part, having the static singleShot()
methods take nanoseconds would be a bit surprising?

[ChangeLog][Core][QObject] Added startTimer() nanoseconds overload and
removed the milliseconds overload. This change is backwards compatible.

Change-Id: I69e79c8feb6354846c6d3be57dc529af7abd1313
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

4 files changed, 43 insertions, 19 deletions

diff --git a/src/corelib/compat/removed_api.cpp b/src/corelib/compat/removed_api.cpp
index a2d8d6f63e..b214ca4f36 100644
--- a/src/corelib/compat/removed_api.cpp
+++ b/src/corelib/compat/removed_api.cpp
@@ -4,6 +4,7 @@
 #define QT_CORE_BUILD_REMOVED_API
 
 #include "qglobal.h"
+#include "qnumeric.h"
 
 QT_USE_NAMESPACE
 
@@ -954,6 +955,20 @@ bool QUrlQuery::operator==(const QUrlQuery &other) const
     return comparesEqual(*this, other);
 }
 
+#include "qobject.h"
+
+int QObject::startTimer(std::chrono::milliseconds time, Qt::TimerType timerType)
+{
+    using namespace std::chrono;
+    using ratio = std::ratio_divide<std::milli, std::nano>;
+    if (nanoseconds::rep r; qMulOverflow<ratio::num>(time.count(), &r)) {
+        qWarning("QObject::startTimer(std::chrono::milliseconds time ...): "
+                 "'time' arg will overflow when converted to nanoseconds.");
+    }
+    return startTimer(nanoseconds{time}, timerType);
+}
+
+
 // #include "qotherheader.h"
 // // implement removed functions from qotherheader.h
 // order sections alphabetically to reduce chances of merge conflicts
diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp
index f386891dc7..828a48e21e 100644
--- a/src/corelib/kernel/qobject.cpp
+++ b/src/corelib/kernel/qobject.cpp
@@ -1850,7 +1850,6 @@ int QObject::startTimer(int interval, Qt::TimerType timerType)
 /*!
     \since 5.9
     \overload
-    \fn int QObject::startTimer(std::chrono::milliseconds interval, Qt::TimerType timerType)
 
     Starts a timer and returns a timer identifier, or returns zero if
     it could not start a timer.
@@ -1884,14 +1883,19 @@ int QObject::startTimer(int interval, Qt::TimerType timerType)
     less clumsy than using timer IDs directly.
 
     \sa timerEvent(), killTimer(), QTimer::singleShot()
+
+    \note Starting from Qt 6.8 the type of \a interval
+    is \c std::chrono::nanoseconds, prior to that it was \c
+    std::chrono::milliseconds. This change is backwards compatible with
+    older releases of Qt.
 */
-int QObject::startTimer(std::chrono::milliseconds interval, Qt::TimerType timerType)
+int QObject::startTimer(std::chrono::nanoseconds interval, Qt::TimerType timerType)
 {
     Q_D(QObject);
 
     using namespace std::chrono_literals;
 
-    if (Q_UNLIKELY(interval < 0ms)) {
+    if (Q_UNLIKELY(interval < 0ns)) {
         qWarning("QObject::startTimer: Timers cannot have negative intervals");
         return 0;
     }
@@ -1907,7 +1911,8 @@ int QObject::startTimer(std::chrono::milliseconds interval, Qt::TimerType timerT
     }
 
     auto dispatcher = thisThreadData->eventDispatcher.loadRelaxed();
-    int timerId = dispatcher->registerTimer(interval.count(), timerType, this);
+    const auto msecs = std::chrono::ceil<std::chrono::milliseconds>(interval);
+    int timerId = dispatcher->registerTimer(msecs.count(), timerType, this);
     d->ensureExtraData();
     d->extraData->runningTimers.append(timerId);
     return timerId;
diff --git a/src/corelib/kernel/qobject.h b/src/corelib/kernel/qobject.h
index 76863d66bc..9d4f4bcbff 100644
--- a/src/corelib/kernel/qobject.h
+++ b/src/corelib/kernel/qobject.h
@@ -19,6 +19,7 @@
 
 #include <QtCore/qobject_impl.h>
 #include <QtCore/qbindingstorage.h>
+#include <QtCore/qtcoreexports.h>
 
 #include <chrono>
 
@@ -141,7 +142,12 @@ public:
     bool moveToThread(QThread *thread QT6_DECL_NEW_OVERLOAD_TAIL);
 
     int startTimer(int interval, Qt::TimerType timerType = Qt::CoarseTimer);
+
+#if QT_CORE_REMOVED_SINCE(6, 8)
     int startTimer(std::chrono::milliseconds time, Qt::TimerType timerType = Qt::CoarseTimer);
+#endif
+    int startTimer(std::chrono::nanoseconds time, Qt::TimerType timerType = Qt::CoarseTimer);
+
     void killTimer(int id);
 
     template<typename T>
diff --git a/src/corelib/kernel/qsingleshottimer_p.h b/src/corelib/kernel/qsingleshottimer_p.h
index aeaf310659..06656ec79c 100644
--- a/src/corelib/kernel/qsingleshottimer_p.h
+++ b/src/corelib/kernel/qsingleshottimer_p.h
@@ -31,12 +31,12 @@ class QSingleShotTimer : public QObject
 
 public:
     inline ~QSingleShotTimer();
-    inline QSingleShotTimer(std::chrono::milliseconds msec, Qt::TimerType timerType, const QObject *r,
-                            const char *member);
-    inline QSingleShotTimer(std::chrono::milliseconds msec, Qt::TimerType timerType, const QObject *r,
-                            QtPrivate::QSlotObjectBase *slotObj);
+    inline QSingleShotTimer(std::chrono::nanoseconds interval, Qt::TimerType timerType,
+                            const QObject *r, const char *member);
+    inline QSingleShotTimer(std::chrono::nanoseconds interval, Qt::TimerType timerType,
+                            const QObject *r, QtPrivate::QSlotObjectBase *slotObj);
 
-    inline void startTimerForReceiver(std::chrono::milliseconds msec, Qt::TimerType timerType,
+    inline void startTimerForReceiver(std::chrono::nanoseconds interval, Qt::TimerType timerType,
                                       const QObject *receiver);
 
 Q_SIGNALS:
@@ -46,15 +46,15 @@ private:
     inline void timerEvent(QTimerEvent *) override;
 };
 
-QSingleShotTimer::QSingleShotTimer(std::chrono::milliseconds msec, Qt::TimerType timerType,
+QSingleShotTimer::QSingleShotTimer(std::chrono::nanoseconds interval, Qt::TimerType timerType,
                                    const QObject *r, const char *member)
     : QObject(QAbstractEventDispatcher::instance())
 {
     connect(this, SIGNAL(timeout()), r, member);
-    startTimerForReceiver(msec, timerType, r);
+    startTimerForReceiver(interval, timerType, r);
 }
 
-QSingleShotTimer::QSingleShotTimer(std::chrono::milliseconds msec, Qt::TimerType timerType,
+QSingleShotTimer::QSingleShotTimer(std::chrono::nanoseconds interval, Qt::TimerType timerType,
                                    const QObject *r, QtPrivate::QSlotObjectBase *slotObj)
     : QObject(QAbstractEventDispatcher::instance())
 {
@@ -63,7 +63,7 @@ QSingleShotTimer::QSingleShotTimer(std::chrono::milliseconds msec, Qt::TimerType
     QObjectPrivate::connectImpl(this, signal_index, r ? r : this, nullptr, slotObj,
                                 Qt::AutoConnection, nullptr, &staticMetaObject);
 
-    startTimerForReceiver(msec, timerType, r);
+    startTimerForReceiver(interval, timerType, r);
 }
 
 QSingleShotTimer::~QSingleShotTimer()
@@ -77,7 +77,7 @@ QSingleShotTimer::~QSingleShotTimer()
     the same thread as where it will be handled, so that it fires reliably even
     if the thread that set up the timer is busy.
 */
-void QSingleShotTimer::startTimerForReceiver(std::chrono::milliseconds msec,
+void QSingleShotTimer::startTimerForReceiver(std::chrono::nanoseconds interval,
                                              Qt::TimerType timerType, const QObject *receiver)
 {
     if (receiver && receiver->thread() != thread()) {
@@ -88,20 +88,18 @@ void QSingleShotTimer::startTimerForReceiver(std::chrono::milliseconds msec,
         setParent(nullptr);
         moveToThread(receiver->thread());
 
-        QDeadlineTimer deadline(msec, timerType);
+        QDeadlineTimer deadline(interval, timerType);
         auto invokable = [this, deadline, timerType] {
             if (deadline.hasExpired()) {
                 Q_EMIT timeout();
             } else {
                 auto nsecs = deadline.remainingTimeAsDuration();
-                // Use std::chrono::ceil<milliseconds> to match what
-                // QDeadlineTimer::remainingTime() did
-                timerId = startTimer(std::chrono::ceil<std::chrono::milliseconds>(nsecs), timerType);
+                timerId = startTimer(nsecs, timerType);
             }
         };
         QMetaObject::invokeMethod(this, invokable, Qt::QueuedConnection);
     } else {
-        timerId = startTimer(msec, timerType);
+        timerId = startTimer(interval, timerType);
     }
 }