4 files changed, 49 insertions, 9 deletions

diff --git a/src/corelib/tools/qarraydata.cpp b/src/corelib/tools/qarraydata.cpp
index 5ed3ce015f..8498d0e4d5 100644
--- a/src/corelib/tools/qarraydata.cpp
+++ b/src/corelib/tools/qarraydata.cpp
@@ -40,6 +40,7 @@
 ****************************************************************************/
 
 #include <QtCore/qarraydata.h>
+#include <QtCore/private/qtools_p.h>
 
 #include <stdlib.h>
 
@@ -63,14 +64,20 @@ QArrayData *QArrayData::allocate(size_t objectSize, size_t alignment,
             ? const_cast<QArrayData *>(&qt_array_empty)
             : const_cast<QArrayData *>(&qt_array_unsharable_empty);
 
-    size_t allocSize = sizeof(QArrayData) + objectSize * capacity;
+    size_t headerSize = sizeof(QArrayData);
 
     // Allocate extra (alignment - Q_ALIGNOF(QArrayData)) padding bytes so we
     // can properly align the data array. This assumes malloc is able to
     // provide appropriate alignment for the header -- as it should!
     // Padding is skipped when allocating a header for RawData.
     if (!(options & RawData))
-        allocSize += (alignment - Q_ALIGNOF(QArrayData));
+        headerSize += (alignment - Q_ALIGNOF(QArrayData));
+
+    // Allocate additional space if array is growing
+    if (options & Grow)
+        capacity = qAllocMore(objectSize * capacity, headerSize) / objectSize;
+
+    size_t allocSize = headerSize + objectSize * capacity;
 
     QArrayData *header = static_cast<QArrayData *>(::malloc(allocSize));
     if (header) {
diff --git a/src/corelib/tools/qarraydata.h b/src/corelib/tools/qarraydata.h
index da2058dccf..351a75aade 100644
--- a/src/corelib/tools/qarraydata.h
+++ b/src/corelib/tools/qarraydata.h
@@ -81,9 +81,10 @@ struct Q_CORE_EXPORT QArrayData
     }
 
     enum AllocationOption {
-        CapacityReserved = 0x1,
-        Unsharable = 0x2,
-        RawData = 0x4,
+        CapacityReserved    = 0x1,
+        Unsharable          = 0x2,
+        RawData             = 0x4,
+        Grow                = 0x8,
 
         Default = 0
     };
diff --git a/tests/auto/corelib/tools/qarraydata/simplevector.h b/tests/auto/corelib/tools/qarraydata/simplevector.h
index a0a9b5f764..fe8108bff2 100644
--- a/tests/auto/corelib/tools/qarraydata/simplevector.h
+++ b/tests/auto/corelib/tools/qarraydata/simplevector.h
@@ -178,7 +178,7 @@ public:
                 || capacity() - size() < size_t(last - first)) {
             SimpleVector detached(Data::allocate(
                         qMax(capacity(), size() + (last - first)),
-                        d->detachFlags()));
+                        d->detachFlags() | Data::Grow));
 
             detached.d->copyAppend(first, last);
             detached.d->copyAppend(begin, begin + d->size);
@@ -199,7 +199,7 @@ public:
                 || capacity() - size() < size_t(last - first)) {
             SimpleVector detached(Data::allocate(
                         qMax(capacity(), size() + (last - first)),
-                        d->detachFlags()));
+                        d->detachFlags() | Data::Grow));
 
             if (d->size) {
                 const T *const begin = constBegin();
@@ -239,7 +239,7 @@ public:
                 || capacity() - size() < size_t(last - first)) {
             SimpleVector detached(Data::allocate(
                         qMax(capacity(), size() + (last - first)),
-                        d->detachFlags()));
+                        d->detachFlags() | Data::Grow));
 
             if (position)
                 detached.d->copyAppend(begin, where);
diff --git a/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp b/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp
index 36bf7516a9..f3f1daba0f 100644
--- a/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp
+++ b/tests/auto/corelib/tools/qarraydata/tst_qarraydata.cpp
@@ -87,6 +87,7 @@ private slots:
     void literals();
     void variadicLiterals();
     void rValueReferences();
+    void grow();
 };
 
 template <class T> const T &const_(const T &t) { return t; }
@@ -651,6 +652,7 @@ void tst_QArrayData::allocate_data()
             QArrayData::CapacityReserved | QArrayData::Unsharable, true, false,
             unsharable_empty },
         { "Unsharable", QArrayData::Unsharable, false, false, unsharable_empty },
+        { "Grow", QArrayData::Grow, false, true, shared_empty }
     };
 
     for (size_t i = 0; i < sizeof(types)/sizeof(types[0]); ++i)
@@ -690,7 +692,10 @@ void tst_QArrayData::allocate()
         keeper.headers.append(data);
 
         QCOMPARE(data->size, 0);
-        QVERIFY(data->alloc >= uint(capacity));
+        if (allocateOptions & QArrayData::Grow)
+            QVERIFY(data->alloc > uint(capacity));
+        else
+            QCOMPARE(data->alloc, uint(capacity));
         QCOMPARE(data->capacityReserved, uint(isCapacityReserved));
         QCOMPARE(data->ref.isSharable(), isSharable);
 
@@ -1385,5 +1390,32 @@ void tst_QArrayData::rValueReferences()
 #endif
 }
 
+void tst_QArrayData::grow()
+{
+    SimpleVector<int> vector;
+
+    QCOMPARE(vector.size(), size_t(0));
+
+    size_t previousCapacity = vector.capacity();
+    size_t allocations = 0;
+    for (size_t i = 1; i <=  (1 << 20); ++i) {
+        int source[1] = { i };
+        vector.append(source, source + 1);
+        QCOMPARE(vector.size(), i);
+        if (vector.capacity() != previousCapacity) {
+            previousCapacity = vector.capacity();
+            ++allocations;
+        }
+    }
+    QCOMPARE(vector.size(), size_t(1 << 20));
+
+    // QArrayData::Grow prevents excessive allocations on a growing container
+    QVERIFY(allocations > 20 / 2);
+    QVERIFY(allocations < 20 * 2);
+
+    for (size_t i = 0; i < (1 << 20); ++i)
+        QCOMPARE(const_(vector).at(i), int(i + 1));
+}
+
 QTEST_APPLESS_MAIN(tst_QArrayData)
 #include "tst_qarraydata.moc"