Source/JavaScriptCore/runtime/SparseArrayValueMap.h

/*
 * Copyright (C) 2011-2021 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
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 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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#pragma once

#include "JSCast.h"
#include "JSTypeInfo.h"
#include "PropertyDescriptor.h"
#include "PutDirectIndexMode.h"
#include "VM.h"
#include "WriteBarrier.h"
#include <wtf/HashMap.h>

namespace JSC {

class SparseArrayValueMap;

class SparseArrayEntry : private WriteBarrier<Unknown> {
    WTF_MAKE_FAST_ALLOCATED;
public:
    using Base = WriteBarrier<Unknown>;

    SparseArrayEntry()
    {
        Base::setWithoutWriteBarrier(jsUndefined());
    }

    void get(JSObject*, PropertySlot&) const;
    void get(PropertyDescriptor&) const;
    bool put(JSGlobalObject*, JSValue thisValue, SparseArrayValueMap*, JSValue, bool shouldThrow);
    JSValue getNonSparseMode() const;
    JSValue getConcurrently() const;

    unsigned attributes() const { return m_attributes; }

    void forceSet(unsigned attributes)
    {
        // FIXME: We can expand this for non x86 environments. Currently, loading ReadOnly | DontDelete property
        // from compiler thread is only supported in X86 architecture because of its TSO nature.
        // https://bugs.webkit.org/show_bug.cgi?id=134641
        if (isX86())
            WTF::storeStoreFence();
        m_attributes = attributes;
    }

    void forceSet(VM& vm, JSCell* map, JSValue value, unsigned attributes)
    {
        Base::set(vm, map, value);
        forceSet(attributes);
    }

    WriteBarrier<Unknown>& asValue() { return *this; }

private:
    unsigned m_attributes { 0 };
};

class SparseArrayValueMap final : public JSCell {
public:
    typedef JSCell Base;
    static constexpr unsigned StructureFlags = Base::StructureFlags | StructureIsImmortal;
    
private:
    typedef HashMap<uint64_t, SparseArrayEntry, WTF::IntHash<uint64_t>, WTF::UnsignedWithZeroKeyHashTraits<uint64_t>> Map;

    enum Flags {
        Normal = 0,
        SparseMode = 1,
        LengthIsReadOnly = 2,
    };

    SparseArrayValueMap(VM&);
    
    void finishCreation(VM&);

public:
    DECLARE_EXPORT_INFO;
    
    typedef Map::iterator iterator;
    typedef Map::const_iterator const_iterator;
    typedef Map::AddResult AddResult;

    static SparseArrayValueMap* create(VM&);
    
    static constexpr bool needsDestruction = true;
    static void destroy(JSCell*);

    template<typename CellType, SubspaceAccess>
    static IsoSubspace* subspaceFor(VM& vm)
    {
        return &vm.sparseArrayValueMapSpace;
    }
    
    static Structure* createStructure(VM&, JSGlobalObject*, JSValue prototype);

    DECLARE_VISIT_CHILDREN;

    bool sparseMode()
    {
        return m_flags & SparseMode;
    }

    void setSparseMode()
    {
        m_flags = static_cast<Flags>(m_flags | SparseMode);
    }

    bool lengthIsReadOnly()
    {
        return m_flags & LengthIsReadOnly;
    }

    void setLengthIsReadOnly()
    {
        m_flags = static_cast<Flags>(m_flags | LengthIsReadOnly);
    }

    // These methods may mutate the contents of the map
    bool putEntry(JSGlobalObject*, JSObject*, unsigned, JSValue, bool shouldThrow);
    bool putDirect(JSGlobalObject*, JSObject*, unsigned, JSValue, unsigned attributes, PutDirectIndexMode);
    AddResult add(JSObject*, unsigned);
    iterator find(unsigned i) { return m_map.find(i); }
    // This should ASSERT the remove is valid (check the result of the find).
    void remove(iterator it);
    void remove(unsigned i);

    JSValue getConcurrently(unsigned index);

    // These methods do not mutate the contents of the map.
    iterator notFound() { return m_map.end(); }
    bool isEmpty() const { return m_map.isEmpty(); }
    bool contains(unsigned i) const { return m_map.contains(i); }
    size_t size() const { return m_map.size(); }
    // Only allow const begin/end iteration.
    const_iterator begin() const { return m_map.begin(); }
    const_iterator end() const { return m_map.end(); }

private:
    Map m_map;
    Flags m_flags { Normal };
    size_t m_reportedCapacity { 0 };
};

} // namespace JSC