QtConcurrent: Fix for leak in QFuture

To avoid leaking when converting a QFuture<T> to a QFuture<void> we need
to have a separate ref. counter for QFuture<T>. When the last QFuture<T>
goes out of scope, we need to clean out the result data.

backported from qt/qtbase commit 731ba8ed08f80644b403556638c7f6229e678ebe
Original commit by Christian Strømme

Task-number: QTBUG-27224
Change-Id: I0c6b525cf241b5c559a1bab4e0066cd4de556ea8
Reviewed-by: Christian Stromme <christian.stromme@digia.com>

1 files changed, 25 insertions, 1 deletions

diff --git a/src/corelib/concurrent/qfutureinterface_p.h b/src/corelib/concurrent/qfutureinterface_p.h
index 407c926137..8431b1ad37 100644
--- a/src/corelib/concurrent/qfutureinterface_p.h
+++ b/src/corelib/concurrent/qfutureinterface_p.h
@@ -129,7 +129,31 @@ class QFutureInterfaceBasePrivate
 public:
     QFutureInterfaceBasePrivate(QFutureInterfaceBase::State initialState);
 
-    QAtomicInt refCount;
+    // When the last QFuture<T> reference is removed, we need to make
+    // sure that data stored in the ResultStore is cleaned out.
+    // Since QFutureInterfaceBasePrivate can be shared between QFuture<T>
+    // and QFuture<void> objects, we use a separate ref. counter
+    // to keep track of QFuture<T> objects.
+    class RefCount
+    {
+    public:
+        inline RefCount(int r = 0, int rt = 0)
+            : m_refCount(r), m_refCountT(rt) {}
+        // Default ref counter for QFIBP
+        inline bool ref() { return m_refCount.ref(); }
+        inline bool deref() { return m_refCount.deref(); }
+        // Ref counter for type T
+        inline bool refT() { return m_refCountT.ref(); }
+        inline bool derefT() { return m_refCountT.deref(); }
+        inline operator int() const { return int(m_refCount); }
+        inline bool operator==(int value) const { return m_refCount == value; }
+
+    private:
+        QAtomicInt m_refCount;
+        QAtomicInt m_refCountT;
+    };
+
+    RefCount refCount;
     mutable QMutex m_mutex;
     QWaitCondition waitCondition;
     QList<QFutureCallOutInterface *> outputConnections;