Optimize QPromise destructor

Unify cancel and finish in QPromise destructor in a single call. This
saves us one extra mutex lock and atomic state change.

Task-number: QTBUG-84977
Change-Id: Iac06302c39a2863008b27325fcf6792d4f58c8ae
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/thread/qfutureinterface.cpp

@@ -110,14 +110,36 @@ static inline int switch_from_to(QAtomicInt &a, int from, int to)
 
 void QFutureInterfaceBase::cancel()
 {
-    QMutexLocker locker(&d->m_mutex);
-    if (d->state.loadRelaxed() & Canceled)
-        return;
+    cancel(CancelMode::CancelOnly);
+}
+
+void QFutureInterfaceBase::cancel(QFutureInterfaceBase::CancelMode mode)
+{
+    QMutexLocker locker(&d->m_mutex);
+
+    const auto oldState = d->state.loadRelaxed();
+
+    switch (mode) {
+    case CancelMode::CancelAndFinish:
+        if ((oldState & Finished) && (oldState & Canceled))
+            return;
+        switch_from_to(d->state, suspendingOrSuspended | Running, Canceled | Finished);
+        break;
+    case CancelMode::CancelOnly:
+        if (oldState & Canceled)
+            return;
+        switch_from_to(d->state, suspendingOrSuspended, Canceled);
+        break;
+    }
 
-    switch_from_to(d->state, suspendingOrSuspended, Canceled);
     d->waitCondition.wakeAll();
     d->pausedWaitCondition.wakeAll();
-    d->sendCallOut(QFutureCallOutEvent(QFutureCallOutEvent::Canceled));
+
+    if (!(oldState & Canceled))
+        d->sendCallOut(QFutureCallOutEvent(QFutureCallOutEvent::Canceled));
+    if (mode == CancelMode::CancelAndFinish && !(oldState & Finished))
+        d->sendCallOut(QFutureCallOutEvent(QFutureCallOutEvent::Finished));
+
     d->isValid = false;
 }
 

src/corelib/thread/qfutureinterface.h

@@ -154,6 +154,8 @@ public:
     int loadState() const;
 
     void cancel();
+    void cancelAndFinish() { cancel(CancelMode::CancelAndFinish); }
+
     void setSuspended(bool suspend);
     void toggleSuspended();
     void reportSuspended() const;
@@ -216,6 +218,9 @@ protected:
     bool launchAsync() const;
 
     bool isRunningOrPending() const;
+
+    enum class CancelMode { CancelOnly, CancelAndFinish };
+    void cancel(CancelMode mode);
 };
 
 inline void swap(QFutureInterfaceBase &lhs, QFutureInterfaceBase &rhs) noexcept

src/corelib/thread/qpromise.h

@@ -70,10 +70,8 @@ public:
             return;
         // Otherwise, if computation is not finished at this point, cancel
         // potential waits
-        if (!(state & QFutureInterfaceBase::State::Finished)) {
-            d.cancel();
-            finish();  // required to finalize the state
-        }
+        if (!(state & QFutureInterfaceBase::State::Finished))
+            d.cancelAndFinish(); // cancel and finalize the state
     }
 
     // Core QPromise APIs

tests/auto/corelib/thread/qfuture/tst_qfuture.cpp

@@ -107,6 +107,7 @@ private slots:
     void futureInterface();
     void refcounting();
     void cancel();
+    void cancelAndFinish();
     void statePropagation();
     void multipleResults();
     void indexedResults();
@@ -865,6 +866,39 @@ void tst_QFuture::cancel()
     }
 }
 
+void tst_QFuture::cancelAndFinish()
+{
+    {
+        QFutureInterface<void> fi;
+
+        fi.reportStarted();
+        fi.cancelAndFinish();
+
+        QVERIFY(fi.isStarted());
+        QVERIFY(!fi.isRunning());
+        QVERIFY(!fi.isSuspended());
+        QVERIFY(!fi.isSuspending());
+        QVERIFY(fi.isCanceled());
+        QVERIFY(fi.isFinished());
+    }
+
+    // The same with suspended state
+    {
+        QFutureInterface<void> fi;
+
+        fi.reportStarted();
+        fi.setSuspended(true);
+        fi.cancelAndFinish();
+
+        QVERIFY(fi.isStarted());
+        QVERIFY(!fi.isRunning());
+        QVERIFY(!fi.isSuspended());
+        QVERIFY(!fi.isSuspending());
+        QVERIFY(fi.isCanceled());
+        QVERIFY(fi.isFinished());
+    }
+}
+
 void tst_QFuture::statePropagation()
 {
     QFuture<void> f1;

tests/auto/corelib/thread/qfuturewatcher/tst_qfuturewatcher.cpp

@@ -46,6 +46,8 @@ private slots:
     void startFinish();
     void progressValueChanged();
     void canceled();
+    void cancelAndFinish_data();
+    void cancelAndFinish();
     void resultAt();
     void resultReadyAt();
     void futureSignals();
@@ -229,6 +231,42 @@ void tst_QFutureWatcher::canceled()
     future.waitForFinished();
 }
 
+void tst_QFutureWatcher::cancelAndFinish_data()
+{
+    QTest::addColumn<bool>("isCanceled");
+    QTest::addColumn<bool>("isFinished");
+
+    QTest::addRow("running") << false << false;
+    QTest::addRow("canceled") << true << false;
+    QTest::addRow("finished") << false << true;
+    QTest::addRow("canceledAndFinished") << true << true;
+}
+
+void tst_QFutureWatcher::cancelAndFinish()
+{
+    QFETCH(bool, isCanceled);
+    QFETCH(bool, isFinished);
+
+    QFutureInterface<void> fi;
+    QFutureWatcher<void> futureWatcher;
+    QSignalSpy finishedSpy(&futureWatcher, &QFutureWatcher<void>::finished);
+    QSignalSpy canceledSpy(&futureWatcher, &QFutureWatcher<void>::canceled);
+    futureWatcher.setFuture(fi.future());
+
+    fi.reportStarted();
+
+    if (isCanceled)
+        fi.cancel();
+    if (isFinished)
+        fi.reportFinished();
+
+    fi.cancelAndFinish();
+
+    // The signals should be emitted only once
+    QTRY_COMPARE(canceledSpy.count(), 1);
+    QTRY_COMPARE(finishedSpy.count(), 1);
+}
+
 class IntTask : public RunFunctionTaskBase<int>
 {
 public: