Add setSharable support in QArrayData stack

Making use of the same feature added in RefCount.

To keep with the intention of avoiding the allocation of "empty" array
headers, this introduces an unsharable_empty, which allows users to
maintain the "unsharable bit" on empty containers, without imposing any
actual allocations.

(Before anyone asks, there is no point to a zero-sized capacity-reserved
container so no other combinations are needed for now.)

Change-Id: Icaa40ac3100ad954fdc20dee0c991861136a5b19
Reviewed-by: Bradley T. Hughes <bradley.hughes@nokia.com>

1 files changed, 11 insertions, 4 deletions

diff --git a/src/corelib/tools/qarraydata.h b/src/corelib/tools/qarraydata.h
index b7ab59257f..1fd60e2155 100644
--- a/src/corelib/tools/qarraydata.h
+++ b/src/corelib/tools/qarraydata.h
@@ -74,12 +74,13 @@ struct Q_CORE_EXPORT QArrayData
     }
 
     static QArrayData *allocate(size_t objectSize, size_t alignment,
-            size_t capacity, bool reserve) Q_REQUIRED_RESULT;
+            size_t capacity, bool reserve, bool sharable) Q_REQUIRED_RESULT;
     static void deallocate(QArrayData *data, size_t objectSize,
             size_t alignment);
 
     static const QArrayData shared_null;
     static const QArrayData shared_empty;
+    static const QArrayData unsharable_empty;
 };
 
 template <class T>
@@ -99,11 +100,11 @@ struct QTypedArrayData
 
     class AlignmentDummy { QArrayData header; T data; };
 
-    static QTypedArrayData *allocate(size_t capacity, bool reserve = false)
-            Q_REQUIRED_RESULT
+    static QTypedArrayData *allocate(size_t capacity, bool reserve = false,
+            bool sharable = true) Q_REQUIRED_RESULT
     {
         return static_cast<QTypedArrayData *>(QArrayData::allocate(sizeof(T),
-                    Q_ALIGNOF(AlignmentDummy), capacity, reserve));
+                    Q_ALIGNOF(AlignmentDummy), capacity, reserve, sharable));
     }
 
     static void deallocate(QArrayData *data)
@@ -122,6 +123,12 @@ struct QTypedArrayData
         return static_cast<QTypedArrayData *>(
                 const_cast<QArrayData *>(&QArrayData::shared_empty));
     }
+
+    static QTypedArrayData *unsharableEmpty()
+    {
+        return static_cast<QTypedArrayData *>(
+                const_cast<QArrayData *>(&QArrayData::unsharable_empty));
+    }
 };
 
 template <class T, size_t N>