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, 11 insertions, 4 deletions

diff --git a/src/corelib/concurrent/qfutureinterface.h b/src/corelib/concurrent/qfutureinterface.h
index 30bfbdb60e..dfe79416de 100644
--- a/src/corelib/concurrent/qfutureinterface.h
+++ b/src/corelib/concurrent/qfutureinterface.h
@@ -132,6 +132,8 @@ public:
 
 protected:
     bool referenceCountIsOne() const;
+    bool refT() const;
+    bool derefT() const;
 public:
 
 #ifndef QFUTURE_TEST
@@ -150,13 +152,17 @@ class QFutureInterface : public QFutureInterfaceBase
 public:
     QFutureInterface(State initialState = NoState)
         : QFutureInterfaceBase(initialState)
-    { }
+    {
+        refT();
+    }
     QFutureInterface(const QFutureInterface &other)
         : QFutureInterfaceBase(other)
-    { }
+    {
+        refT();
+    }
     ~QFutureInterface()
     {
-        if (referenceCountIsOne())
+        if (!derefT())
             resultStore().clear();
     }
 
@@ -165,7 +171,8 @@ public:
 
     QFutureInterface &operator=(const QFutureInterface &other)
     {
-        if (referenceCountIsOne())
+        other.refT();
+        if (!derefT())
             resultStore().clear();
         QFutureInterfaceBase::operator=(other);
         return *this;