From c000143ee472fc613b91a4f16f321509e4f0ee18 Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Wed, 15 Jun 2016 00:34:10 -0700
Subject: [PATCH] QDeadlineTimer: optimize when std::chrono::steady_clock is
 the same

Change-Id: Ib57b52598e2f452985e9fffd14583173716343b0
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/kernel/qdeadlinetimer.h           | 28 +++++++++++++++++++
 .../qdeadlinetimer/tst_qdeadlinetimer.cpp     | 12 ++++++++
 2 files changed, 40 insertions(+)

diff --git a/src/corelib/kernel/qdeadlinetimer.h b/src/corelib/kernel/qdeadlinetimer.h
index 180d5fe4317..8ec9380916c 100644
--- a/src/corelib/kernel/qdeadlinetimer.h
+++ b/src/corelib/kernel/qdeadlinetimer.h
@@ -192,6 +192,34 @@ public:
     QPair<qint64, unsigned> _q_data() const { return qMakePair(t1, t2); }
 };
 
+#if QT_HAS_INCLUDE(<chrono>) && (defined(Q_OS_DARWIN) || defined(Q_OS_LINUX) || (defined(Q_CC_MSVC) && Q_CC_MSVC >= 1900))
+// We know for these OS/compilers that the std::chrono::steady_clock uses the same
+// reference time as QDeadlineTimer
+
+template <> inline std::chrono::steady_clock::time_point
+QDeadlineTimer::deadline<std::chrono::steady_clock, std::chrono::steady_clock::duration>() const
+{
+    return std::chrono::steady_clock::time_point(std::chrono::nanoseconds(deadlineNSecs()));
+}
+
+template <> inline void
+QDeadlineTimer::setDeadline<std::chrono::steady_clock, std::chrono::steady_clock::duration>(std::chrono::steady_clock::time_point tp, Qt::TimerType type_)
+{
+    using namespace std::chrono;
+    if (tp == tp.max()) {
+        *this = Forever;
+        type = type_;
+    } else if (type_ != Qt::PreciseTimer) {
+        // if we aren't using PreciseTimer, then we need to convert
+        setPreciseRemainingTime(0, duration_cast<nanoseconds>(tp - steady_clock::now()).count(), type_);
+    } else {
+        setPreciseDeadline(0,
+                           duration_cast<nanoseconds>(tp.time_since_epoch()).count(),
+                           type_);
+    }
+}
+#endif
+
 Q_DECLARE_SHARED(QDeadlineTimer)
 
 QT_END_NAMESPACE
diff --git a/tests/auto/corelib/kernel/qdeadlinetimer/tst_qdeadlinetimer.cpp b/tests/auto/corelib/kernel/qdeadlinetimer/tst_qdeadlinetimer.cpp
index e4ab2eb1db4..74ab52ee7ea 100644
--- a/tests/auto/corelib/kernel/qdeadlinetimer/tst_qdeadlinetimer.cpp
+++ b/tests/auto/corelib/kernel/qdeadlinetimer/tst_qdeadlinetimer.cpp
@@ -596,6 +596,18 @@ void tst_QDeadlineTimer::stdchrono()
     QTRY_VERIFY2_WITH_TIMEOUT(timersExecuted,
         "Looks like timers didn't fire on time.", 4 * minResolution);
 
+#if defined(Q_OS_DARWIN) || defined(Q_OS_LINUX) || (defined(Q_CC_MSVC) && Q_CC_MSVC >= 1900)
+    {
+        // We know for these OS/compilers that the std::chrono::steady_clock uses the same
+        // reference time as QDeadlineTimer
+        qint64 before = duration_cast<nanoseconds>(steady_before.time_since_epoch()).count();
+        qint64 after = duration_cast<nanoseconds>(steady_after.time_since_epoch()).count();
+        QVERIFY2(now.deadlineNSecs() > before, QByteArray::number(now.deadlineNSecs()) +
+                 " > " + QByteArray::number(before));
+        QVERIFY2(now.deadlineNSecs() < after, QByteArray::number(now.deadlineNSecs()) +
+                 " < " + QByteArray::number(after));
+    }
+#endif
     {
         auto diff = duration_cast<milliseconds>(steady_after - steady_deadline);
         QVERIFY2(diff.count() > minResolution / 2, QByteArray::number(qint64(diff.count())));