add QList::reserve()

while this reserves memory "only" for the pointer list, this still
amounts to 100% of the re-allocs for small simple types. for
big/complex/static types the gain is lower, but still.

Reviewed-by: Denis
Reviewed-by: Joao

1 files changed, 23 insertions, 3 deletions

diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index 1d08c41d74..3b9eefa1f8 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -72,9 +72,10 @@ struct Q_CORE_EXPORT QListData {
     };
     enum { DataHeaderSize = sizeof(Data) - sizeof(void *) };
 
+    Data *detach(int alloc);
     Data *detach(); // remove in 5.0
     Data *detach2(); // remove in 5.0
-    Data *detach3();
+    Data *detach3(); // remove in 5.0
     void realloc(int alloc);
     static Data shared_null;
     Data *d;
@@ -140,6 +141,7 @@ public:
     const T &operator[](int i) const;
     T &operator[](int i);
 
+    void reserve(int size);
     void append(const T &t);
     void append(const QList<T> &t);
     void prepend(const T &t);
@@ -331,6 +333,7 @@ public:
 #endif
 
 private:
+    void detach_helper(int alloc);
     void detach_helper();
     void free(QListData::Data *d);
 
@@ -464,6 +467,17 @@ inline T QList<T>::takeLast()
 { T t = last(); removeLast(); return t; }
 
 template <typename T>
+Q_OUTOFLINE_TEMPLATE void QList<T>::reserve(int alloc)
+{
+    if (d->alloc < alloc) {
+        if (d->ref != 1)
+            detach_helper(alloc);
+        else
+            p.realloc(alloc);
+    }
+}
+
+template <typename T>
 Q_OUTOFLINE_TEMPLATE void QList<T>::append(const T &t)
 {
     detach();
@@ -599,10 +613,10 @@ Q_OUTOFLINE_TEMPLATE T QList<T>::value(int i, const T& defaultValue) const
 }
 
 template <typename T>
-Q_OUTOFLINE_TEMPLATE void QList<T>::detach_helper()
+Q_OUTOFLINE_TEMPLATE void QList<T>::detach_helper(int alloc)
 {
     Node *n = reinterpret_cast<Node *>(p.begin());
-    QListData::Data *x = p.detach3();
+    QListData::Data *x = p.detach(alloc);
     QT_TRY {
         node_copy(reinterpret_cast<Node *>(p.begin()), reinterpret_cast<Node *>(p.end()), n);
     } QT_CATCH(...) {
@@ -616,6 +630,12 @@ Q_OUTOFLINE_TEMPLATE void QList<T>::detach_helper()
 }
 
 template <typename T>
+Q_OUTOFLINE_TEMPLATE void QList<T>::detach_helper()
+{
+    detach_helper(d->alloc);
+}
+
+template <typename T>
 Q_OUTOFLINE_TEMPLATE QList<T>::~QList()
 {
     if (d && !d->ref.deref())