QList: re-use the prepend buffer, if any, on assign()
Task-number: QTBUG-106196 Change-Id: I62d8610529cab528ae1b114d29707133b4fc28dc Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io> Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
This commit is contained in:
Marc Mutz
parent
06830bd78d
commit
782ccc6de5
@ -8,6 +8,7 @@
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#include <QtCore/qcontainertools_impl.h>
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#include <QtCore/q20functional.h>
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#include <QtCore/q20memory.h>
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QT_BEGIN_NAMESPACE
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@ -317,9 +318,7 @@ public:
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if constexpr (IsFwdIt) {
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const qsizetype n = std::distance(first, last);
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// Use of freeSpaceAtBegin() isn't, yet, implemented.
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const auto usableCapacity = constAllocatedCapacity() - freeSpaceAtBegin();
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if (needsDetach() || n > usableCapacity) {
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if (needsDetach() || n > constAllocatedCapacity()) {
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QArrayDataPointer allocated(Data::allocate(detachCapacity(n)));
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swap(allocated);
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}
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@ -329,8 +328,48 @@ public:
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// We don't want to copy data that we know we'll overwrite
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}
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auto dst = begin();
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auto offset = freeSpaceAtBegin();
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const auto capacityBegin = begin() - offset;
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const auto prependBufferEnd = begin();
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if constexpr (!std::is_nothrow_constructible_v<T, decltype(proj(*first))>) {
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// If construction can throw, and we have freeSpaceAtBegin(),
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// it's easiest to just clear the container and start fresh.
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// The alternative would be to keep track of two active, disjoint ranges.
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if (offset) {
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(*this)->truncate(0);
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setBegin(capacityBegin);
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offset = 0;
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}
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}
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auto dst = capacityBegin;
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const auto dend = end();
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if (offset) { // avoids dead stores
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setBegin(capacityBegin); // undo prepend optimization
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// By construction, the following loop is nothrow!
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// (otherwise, we can't reach here)
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// Assumes InputIterator operations don't throw.
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// (but we can't statically assert that, as these operations
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// have preconditons, so typically aren't noexcept)
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while (true) {
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if (dst == prependBufferEnd) { // ran out of prepend buffer space
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size += offset;
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// we now have a contiguous buffer, continue with the main loop:
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break;
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}
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if (first == last) { // ran out of elements to assign
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std::destroy(prependBufferEnd, dend);
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size = dst - begin();
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return;
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}
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q20::construct_at(dst, proj(*first)); // construct element in prepend buffer
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++dst;
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++first;
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}
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}
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while (true) {
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if (first == last) { // ran out of elements to assign
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std::destroy(dst, dend);
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@ -234,6 +234,12 @@ private slots:
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void assignInt() const { assign<int>(); }
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void assignMovable() const { assign<Movable>(); }
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void assignCustom() const { assign<Custom>(); }
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void assignUsesPrependBuffer_int_data() { assignUsesPrependBuffer_data(); }
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void assignUsesPrependBuffer_int() const { assignUsesPrependBuffer<int>(); }
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void assignUsesPrependBuffer_Movable_data() { assignUsesPrependBuffer_data(); }
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void assignUsesPrependBuffer_Movable() const { assignUsesPrependBuffer<Movable>(); }
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void assignUsesPrependBuffer_Custom_data() { assignUsesPrependBuffer_data(); }
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void assignUsesPrependBuffer_Custom() const { assignUsesPrependBuffer<Custom>(); }
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void at() const;
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void capacityInt() const { capacity<int>(); }
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void capacityMovable() const { capacity<Movable>(); }
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@ -400,6 +406,8 @@ private:
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template<typename T> void add() const;
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template<typename T> void append() const;
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template<typename T> void assign() const;
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void assignUsesPrependBuffer_data() const;
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template<typename T> void assignUsesPrependBuffer() const;
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template<typename T> void assignFromInitializerList() const;
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template<typename T> void capacity() const;
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template<typename T> void clear() const;
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@ -796,21 +804,98 @@ void tst_QList::assign() const
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QVERIFY(!myvecCopy.isSharedWith(myvec));
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QCOMPARE(myvecCopy, QList<T>() << T_FOO << T_FOO);
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}
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}
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inline namespace Scenarios {
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Q_NAMESPACE
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enum ListState {
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UnsharedList,
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SharedList,
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};
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Q_ENUM_NS(ListState)
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enum RelationWithPrependBuffer {
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FitsIntoFreeSpaceAtBegin,
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FitsFreeSpaceAtBeginExactly,
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ExceedsFreeSpaceAtBegin,
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FitsFreeSpaceAtBeginPlusSizeExactly,
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FullCapacity,
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};
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Q_ENUM_NS(RelationWithPrependBuffer)
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} // namespace Scenarios
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void tst_QList::assignUsesPrependBuffer_data() const
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{
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QTest::addColumn<ListState>("listState");
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QTest::addColumn<RelationWithPrependBuffer>("relationWithPrependBuffer");
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const auto sme = QMetaEnum::fromType<ListState>();
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const auto rme = QMetaEnum::fromType<RelationWithPrependBuffer>();
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for (int i = 0, s = sme.value(i); s != -1; s = sme.value(++i)) {
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for (int j = 0, r = rme.value(j); r != -1; r = rme.value(++j)) {
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QTest::addRow("%s-%s", sme.key(i), rme.key(j))
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<< ListState(s) << RelationWithPrependBuffer(r);
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}
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}
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}
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template <typename T>
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void tst_QList::assignUsesPrependBuffer() const
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{
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QFETCH(const ListState, listState);
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QFETCH(const RelationWithPrependBuffer, relationWithPrependBuffer);
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const auto capBegin = [](const QList<T> &l) {
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return l.begin() - l.d.freeSpaceAtBegin();
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};
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const auto capEnd = [](const QList<T> &l) {
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return l.end() + l.d.freeSpaceAtEnd();
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};
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TST_QLIST_CHECK_LEAKS(T)
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{
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// Test the prepend optimization.
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QList<T> withFreeSpaceAtBegin(16, T_FOO);
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// try at most 100 times to create freeSpaceAtBegin():
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for (int i = 0; i < 100 && !withFreeSpaceAtBegin.d.freeSpaceAtBegin(); ++i)
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for (int i = 0; i < 100 && withFreeSpaceAtBegin.d.freeSpaceAtBegin() < 2; ++i)
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withFreeSpaceAtBegin.prepend(T_FOO);
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QCOMPARE_GT(withFreeSpaceAtBegin.d.freeSpaceAtBegin(), 0);
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const auto oldData = withFreeSpaceAtBegin.constData();
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std::vector<T> v(withFreeSpaceAtBegin.capacity(), T_BAR);
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withFreeSpaceAtBegin.assign(v.begin(), v.end());
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QCOMPARE_EQ(withFreeSpaceAtBegin.d.freeSpaceAtBegin(), 0);
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// TODO: Check for equality after the prepend optimization
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// the following test checks that we didn't reallocate, but re-used the prepend buffer
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QEXPECT_FAIL("","Use of freeSpaceAtBegin() isn't, yet, implemented", Continue);
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QVERIFY(QtPrivate::q_points_into_range(oldData, withFreeSpaceAtBegin));
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QCOMPARE_GT(withFreeSpaceAtBegin.d.freeSpaceAtBegin(), 1);
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auto c = [&] {
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switch (listState) {
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case UnsharedList: return std::move(withFreeSpaceAtBegin);
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case SharedList: return withFreeSpaceAtBegin;
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}
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Q_UNREACHABLE_RETURN(withFreeSpaceAtBegin);
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}();
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const auto n = [&] () -> qsizetype {
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switch (relationWithPrependBuffer) {
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case FitsIntoFreeSpaceAtBegin:
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return qsizetype(1);
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case FitsFreeSpaceAtBeginExactly:
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return c.d.freeSpaceAtBegin();
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case ExceedsFreeSpaceAtBegin:
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return c.d.freeSpaceAtBegin() + 1;
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case FitsFreeSpaceAtBeginPlusSizeExactly:
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return c.d.freeSpaceAtBegin() + c.size();
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case FullCapacity:
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return c.capacity();
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};
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Q_UNREACHABLE_RETURN(0);
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}();
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const auto oldCapBegin = capBegin(c);
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const auto oldCapEnd = capEnd(c);
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const std::vector v(n, T_BAR);
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c.assign(v.begin(), v.end());
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QCOMPARE_EQ(c.d.freeSpaceAtBegin(), 0); // we used the prepend-buffer
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if (listState != SharedList) {
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// check that we didn't reallocate
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QCOMPARE_EQ(capBegin(c), oldCapBegin);
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QCOMPARE_EQ(capEnd(c), oldCapEnd);
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}
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}
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}
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