Source/JavaScriptCore/runtime/CagedBarrierPtr.h

/*
 * Copyright (C) 2017 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
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 *
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 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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#pragma once

#include "AuxiliaryBarrier.h"
#include <wtf/CagedPtr.h>

namespace JSC {

class JSCell;
class VM;

// This is a convenient combo of AuxiliaryBarrier and CagedPtr.

template<Gigacage::Kind passedKind, typename T, bool shouldTag = false>
class CagedBarrierPtr {
public:
    static constexpr Gigacage::Kind kind = passedKind;
    using Type = T;
    using CagedType = CagedPtr<kind, Type, shouldTag>;
    
    CagedBarrierPtr() = default;
    
    template<typename U>
    CagedBarrierPtr(VM& vm, JSCell* cell, U&& value, size_t size)
    {
        m_barrier.set(vm, cell, CagedType(std::forward<U>(value), size));
    }
    
    void clear() { m_barrier.clear(); }
    
    template<typename U>
    void set(VM& vm, JSCell* cell, U&& value, size_t size)
    {
        m_barrier.set(vm, cell, CagedType(std::forward<U>(value), size));
    }
    
    T* get(size_t size) const { return m_barrier.get().get(size); }
    T* getMayBeNull(size_t size) const { return m_barrier.get().getMayBeNull(size); }
    T* getUnsafe() const { return m_barrier.get().getUnsafe(); }

    // We need the template here so that the type of U is deduced at usage time rather than class time. U should always be T.
    template<typename U = T>
    typename std::enable_if<!std::is_same<void, U>::value, T>::type&
    /* T& */ at(size_t index, size_t size) const { return get(size)[index]; }

    bool operator==(const CagedBarrierPtr& other) const
    {
        return m_barrier.get() == other.m_barrier.get();
    }
    
    bool operator!=(const CagedBarrierPtr& other) const
    {
        return !(*this == other);
    }
    
    explicit operator bool() const
    {
        return !!m_barrier.get();
    }
    
    template<typename U>
    void setWithoutBarrier(U&& value, size_t size) { m_barrier.setWithoutBarrier(CagedType(std::forward<U>(value), size)); }

    T* rawBits() const
    {
        return m_barrier.get().rawBits();
    }
    
private:
    AuxiliaryBarrier<CagedType> m_barrier;
};

} // namespace JSC