avoid double reallocations in appending operations

operator+=() and co. would first detach, and then realloc if they found
the reservation too small. in particular, appending anything to an empty
list would trigger this double reallocation (first copy shared_null,
then grow the copy).

Reviewed-by: joao
Reviewed-by: denis

1 files changed, 18 insertions, 0 deletions

diff --git a/src/corelib/tools/qlist.cpp b/src/corelib/tools/qlist.cpp
index ac0dc46..a468c77 100644
--- a/src/corelib/tools/qlist.cpp
+++ b/src/corelib/tools/qlist.cpp
@@ -154,6 +154,19 @@ QListData::Data *QListData::detach(int alloc)
 }
 
 /*!
+ *  Detaches the QListData by allocating new memory for a list which will be bigger
+ *  than the copied one and is expected to grow further.
+ *  Returns the old (shared) data, it is up to the caller to deref() and free()
+ *  For the new data node_copy needs to be called.
+ *
+ *  \internal
+ */
+QListData::Data *QListData::detach_grow(int alloc)
+{
+    return detach(grow(alloc));
+}
+
+/*!
  *  Detaches the QListData by reallocating new memory.
  *  Returns the old (shared) data, it is up to the caller to deref() and free()
  *  For the new data node_copy needs to be called.
@@ -596,6 +609,11 @@ void **QListData::erase(void **xi)
     \internal
 */
 
+/*! \fn void QList::detach_grow(int alloc)
+
+    \internal
+*/
+
 /*! \fn void QList::detachShared()
 
     \internal