4 files changed, 86 insertions, 3 deletions

diff --git a/src/corelib/thread/qfutureinterface.cpp b/src/corelib/thread/qfutureinterface.cpp
index f29f950a1f..dfc905e828 100644
--- a/src/corelib/thread/qfutureinterface.cpp
+++ b/src/corelib/thread/qfutureinterface.cpp
@@ -858,12 +858,25 @@ void QFutureInterfaceBase::setContinuation(std::function<void(const QFutureInter
     }
 }
 
+void QFutureInterfaceBase::cleanContinuation()
+{
+    if (!d)
+        return;
+
+    // This is called when the associated QPromise is being destroyed.
+    // Clear the continuation, to make sure it doesn't keep any ref-counted
+    // copies of this, so that the allocated memory can be freed.
+    QMutexLocker lock(&d->continuationMutex);
+    d->continuation = nullptr;
+}
+
 void QFutureInterfaceBase::runContinuation() const
 {
     QMutexLocker lock(&d->continuationMutex);
     if (d->continuation) {
+        auto fn = std::exchange(d->continuation, nullptr);
         lock.unlock();
-        d->continuation(*this);
+        fn(*this);
     }
 }
 
diff --git a/src/corelib/thread/qfutureinterface.h b/src/corelib/thread/qfutureinterface.h
index 3130c91420..205b2de9f9 100644
--- a/src/corelib/thread/qfutureinterface.h
+++ b/src/corelib/thread/qfutureinterface.h
@@ -212,10 +212,14 @@ private:
     friend class QtPrivate::FailureHandler;
 #endif
 
+    template<class T>
+    friend class QPromise;
+
 protected:
     void setContinuation(std::function<void(const QFutureInterfaceBase &)> func);
     void setContinuation(std::function<void(const QFutureInterfaceBase &)> func,
                          QFutureInterfaceBasePrivate *continuationFutureData);
+    void cleanContinuation();
     void runContinuation() const;
 
     void setLaunchAsync(bool value);
diff --git a/src/corelib/thread/qpromise.h b/src/corelib/thread/qpromise.h
index a970f40d12..f62a2a54e3 100644
--- a/src/corelib/thread/qpromise.h
+++ b/src/corelib/thread/qpromise.h
@@ -66,12 +66,16 @@ public:
     {
         const int state = d.loadState();
         // If QFutureInterface has no state, there is nothing to be done
-        if (state == static_cast<int>(QFutureInterfaceBase::State::NoState))
+        if (state == static_cast<int>(QFutureInterfaceBase::State::NoState)) {
+            d.cleanContinuation();
             return;
+        }
         // Otherwise, if computation is not finished at this point, cancel
         // potential waits
-        if (!(state & QFutureInterfaceBase::State::Finished))
+        if (!(state & QFutureInterfaceBase::State::Finished)) {
             d.cancelAndFinish(); // cancel and finalize the state
+            d.cleanContinuation();
+        }
     }
 
     // Core QPromise APIs
diff --git a/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp b/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp
index 7b272cf5a3..943ea2ea34 100644
--- a/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp
+++ b/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp
@@ -194,6 +194,8 @@ private slots:
     void whenAnyDifferentTypesWithCanceled();
     void whenAnyDifferentTypesWithFailed();
 
+    void continuationsDontLeak();
+
 private:
     using size_type = std::vector<int>::size_type;
 
@@ -4355,5 +4357,65 @@ void tst_QFuture::whenAnyDifferentTypesWithFailed()
 #endif
 }
 
+struct InstanceCounter
+{
+    InstanceCounter() { ++count; }
+    InstanceCounter(const InstanceCounter &) { ++count; }
+    ~InstanceCounter() { --count; }
+    static int count;
+};
+int InstanceCounter::count = 0;
+
+void tst_QFuture::continuationsDontLeak()
+{
+    {
+        // QFuture isn't started and isn't finished (has no state)
+        QPromise<InstanceCounter> promise;
+        auto future = promise.future();
+
+        bool continuationIsRun = false;
+        future.then([future, &continuationIsRun](InstanceCounter) { continuationIsRun = true; });
+
+        promise.addResult(InstanceCounter {});
+
+        QVERIFY(!continuationIsRun);
+    }
+    QCOMPARE(InstanceCounter::count, 0);
+
+    {
+        // QFuture is started, but not finished
+        QPromise<InstanceCounter> promise;
+        auto future = promise.future();
+
+        bool continuationIsRun = false;
+        future.then([future, &continuationIsRun](InstanceCounter) { continuationIsRun = true; });
+
+        promise.start();
+        promise.addResult(InstanceCounter {});
+
+        QVERIFY(!continuationIsRun);
+    }
+    QCOMPARE(InstanceCounter::count, 0);
+
+    {
+        // QFuture is started and finished, the continuation is run
+        QPromise<InstanceCounter> promise;
+        auto future = promise.future();
+
+        bool continuationIsRun = false;
+        future.then([future, &continuationIsRun](InstanceCounter) {
+            QVERIFY(future.isFinished());
+            continuationIsRun = true;
+        });
+
+        promise.start();
+        promise.addResult(InstanceCounter {});
+        promise.finish();
+
+        QVERIFY(continuationIsRun);
+    }
+    QCOMPARE(InstanceCounter::count, 0);
+}
+
 QTEST_MAIN(tst_QFuture)
 #include "tst_qfuture.moc"