| 1 | // Copyright (C) 2016 The Qt Company Ltd. |
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| 2 | // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only |
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| 3 | #ifndef QV4WRITEBARRIER_P_H |
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| 4 | #define QV4WRITEBARRIER_P_H |
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| 5 | |
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| 6 | // |
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| 7 | // W A R N I N G |
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| 8 | // ------------- |
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| 9 | // |
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| 10 | // This file is not part of the Qt API. It exists purely as an |
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| 11 | // implementation detail. This header file may change from version to |
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| 12 | // version without notice, or even be removed. |
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| 13 | // |
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| 14 | // We mean it. |
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| 15 | // |
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| 16 | |
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| 17 | #include <private/qv4global_p.h> |
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| 18 | #include <private/qv4enginebase_p.h> |
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| 19 | |
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| 20 | QT_BEGIN_NAMESPACE |
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| 21 | |
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| 22 | namespace QV4 { |
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| 23 | struct EngineBase; |
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| 24 | typedef quint64 ReturnedValue; |
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| 25 | |
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| 26 | struct WriteBarrier { |
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| 27 | |
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| 28 | static constexpr bool isInsertionBarrier = true; |
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| 29 | |
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| 30 | Q_ALWAYS_INLINE static void write(EngineBase *engine, Heap::Base *base, ReturnedValue *slot, ReturnedValue value) |
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| 31 | { |
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| 32 | if (engine->isGCOngoing) |
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| 33 | write_slowpath(engine, base, slot, value); |
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| 34 | *slot = value; |
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| 35 | } |
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| 36 | Q_QML_EXPORT Q_NEVER_INLINE static void write_slowpath( |
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| 37 | EngineBase *engine, Heap::Base *base, |
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| 38 | ReturnedValue *slot, ReturnedValue value); |
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| 39 | |
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| 40 | Q_ALWAYS_INLINE static void write(EngineBase *engine, Heap::Base *base, Heap::Base **slot, Heap::Base *value) |
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| 41 | { |
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| 42 | if (engine->isGCOngoing) |
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| 43 | write_slowpath(engine, base, slot, value); |
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| 44 | *slot = value; |
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| 45 | } |
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| 46 | Q_QML_EXPORT Q_NEVER_INLINE static void write_slowpath( |
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| 47 | EngineBase *engine, Heap::Base *base, |
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| 48 | Heap::Base **slot, Heap::Base *value); |
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| 49 | |
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| 50 | // MemoryManager isn't a complete type here, so make Engine a template argument |
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| 51 | // so that we can still call engine->memoryManager->markStack() |
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| 52 | template<typename F, typename Engine = EngineBase> |
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| 53 | static void markCustom(Engine *engine, F &&markFunction) { |
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| 54 | if (engine->isGCOngoing) |
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| 55 | (std::forward<F>(markFunction))(engine->memoryManager->markStack()); |
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| 56 | } |
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| 57 | |
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| 58 | // HeapObjectWrapper(Base) are helper classes to ensure that |
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| 59 | // we always use a WriteBarrier when setting heap-objects |
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| 60 | // they are also trivial; if triviality is not required, use Pointer instead |
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| 61 | struct HeapObjectWrapperBase |
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| 62 | { |
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| 63 | // enum class avoids accidental construction via brace-init |
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| 64 | enum class PointerWrapper : quintptr {}; |
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| 65 | PointerWrapper wrapped; |
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| 66 | |
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| 67 | void clear() { wrapped = PointerWrapper(quintptr(0)); } |
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| 68 | }; |
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| 69 | |
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| 70 | template<typename HeapType> |
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| 71 | struct HeapObjectWrapperCommon : HeapObjectWrapperBase |
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| 72 | { |
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| 73 | HeapType *get() const { return reinterpret_cast<HeapType *>(wrapped); } |
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| 74 | operator HeapType *() const { return get(); } |
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| 75 | HeapType * operator->() const { return get(); } |
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| 76 | |
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| 77 | template <typename ConvertibleToHeapType> |
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| 78 | void set(QV4::EngineBase *engine, ConvertibleToHeapType *heapObject) |
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| 79 | { |
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| 80 | WriteBarrier::markCustom(engine, [heapObject](QV4::MarkStack *ms){ |
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| 81 | if (heapObject) |
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| 82 | heapObject->mark(ms); |
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| 83 | }); |
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| 84 | wrapped = static_cast<HeapObjectWrapperBase::PointerWrapper>(quintptr(heapObject)); |
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| 85 | } |
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| 86 | }; |
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| 87 | |
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| 88 | // all types are trivial; we however want to block copies bypassing the write barrier |
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| 89 | // therefore, all members use a PhantomTag to reduce the likelihood |
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| 90 | template<typename HeapType, int PhantomTag> |
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| 91 | struct HeapObjectWrapper : HeapObjectWrapperCommon<HeapType> {}; |
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| 92 | |
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| 93 | /* similar Heap::Pointer, but without the Base conversion (and its inUse assert) |
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| 94 | and for storing references in engine classes stored on the native heap |
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| 95 | Stores a "non-owning" reference to a heap-item (in the C++ sense), but should |
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| 96 | generally mark the heap-item; therefore set goes through a write-barrier |
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| 97 | */ |
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| 98 | template<typename T> |
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| 99 | struct Pointer |
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| 100 | { |
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| 101 | Pointer() = default; |
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| 102 | ~Pointer() = default; |
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| 103 | Q_DISABLE_COPY_MOVE(Pointer) |
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| 104 | T* operator->() const { return get(); } |
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| 105 | operator T* () const { return get(); } |
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| 106 | |
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| 107 | void set(EngineBase *e, T *newVal) { |
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| 108 | WriteBarrier::markCustom(e, [newVal](QV4::MarkStack *ms) { |
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| 109 | if (newVal) |
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| 110 | newVal->mark(ms); |
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| 111 | }); |
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| 112 | ptr = newVal; |
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| 113 | } |
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| 114 | |
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| 115 | T* get() const { return ptr; } |
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| 116 | |
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| 117 | |
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| 118 | |
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| 119 | private: |
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| 120 | T *ptr = nullptr; |
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| 121 | }; |
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| 122 | }; |
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| 123 | |
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| 124 | // ### this needs to be filled with a real memory fence once marking is concurrent |
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| 125 | Q_ALWAYS_INLINE void fence() {} |
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| 126 | |
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| 127 | } |
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| 128 | |
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| 129 | QT_END_NAMESPACE |
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| 130 | |
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| 131 | #endif |
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| 132 | |
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