Add support for creating the object alongside the Data structure in

one go.

This avoids one memory allocation. Currently, we only support calling
the default constructors. I will *NOT* implement argument passing for
C++03. I will implement it with rvalue references for C++0x-capable
compilers.

1 files changed, 47 insertions, 0 deletions

diff --git a/src/corelib/tools/qsharedpointer_impl.h b/src/corelib/tools/qsharedpointer_impl.h
index df31fec..cb78f29 100644
--- a/src/corelib/tools/qsharedpointer_impl.h
+++ b/src/corelib/tools/qsharedpointer_impl.h
@@ -48,6 +48,7 @@
 #pragma qt_sync_stop_processing
 #endif
 
+#include <new>
 #include <QtCore/qatomic.h>
 #include <QtCore/qobject.h>    // for qobject_cast
 
@@ -190,6 +191,34 @@ namespace QtSharedPointer {
     };
 
     template <class T>
+    struct ExternalRefCountWithContiguousData: public ExternalRefCountData
+    {
+#ifdef Q_DECL_ALIGN
+# ifdef Q_ALIGNOF
+#   define QSP_ALIGNOF(T) Q_ALIGNOF(T)
+# else
+#   define QSP_ALIGNOF(T) (sizeof(T) >= 16 ? 16 : sizeof(T) >= 8 ? 8 : sizeof(T) >= 4 ? 4 : sizeof(T) >= 2 ? 2 : 1)
+# endif
+
+        char data[sizeof(T)] Q_DECL_ALIGN(QSP_ALIGNOF(T));
+        inline T *pointer() { return reinterpret_cast<T *>(data); }
+
+# undef QSP_ALIGNOF
+#else
+        union {
+            char data[sizeof(T) + 16];
+            double dummy1;
+# ifndef Q_OS_DARWIN
+            long double dummy2;
+# endif
+        };
+        inline T *pointer() { return reinterpret_cast<T *>(data + 16 - (quintptr(data) & 0xf)); }
+#endif
+
+        inline bool destroy() { this->pointer()->~T(); return true; }
+    };
+
+    template <class T>
     class ExternalRefCount: public Basic<T>
     {
         typedef ExternalRefCountData Data;
@@ -220,6 +249,16 @@ namespace QtSharedPointer {
                 d = new ExternalRefCountWithSpecializedDeleter<T, Deleter>(ptr, deleter);
         }
 
+        inline void internalCreate()
+        {
+            ExternalRefCountWithContiguousData<T> *dd = new ExternalRefCountWithContiguousData<T>;
+            T *ptr = dd->pointer();
+            new (ptr) T(); // create
+
+            Basic<T>::internalConstruct(ptr);
+            d = dd;
+        }
+
         inline ExternalRefCount() : d(0) { }
         inline ~ExternalRefCount() { if (d && !deref()) delete d; }
         inline ExternalRefCount(const ExternalRefCount<T> &other) : Basic<T>(other), d(other.d)
@@ -347,6 +386,14 @@ public:
     inline void clear() { *this = QSharedPointer<T>(); }
 
     QWeakPointer<T> toWeakRef() const;
+
+public:
+    static QSharedPointer<T> create()
+    {
+        QSharedPointer<T> result;
+        result.internalCreate();
+        return result;
+    }
 };
 
 template <class T>