refcnt.hh

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#ifndef __BASE_REFCNT_HH__
#define __BASE_REFCNT_HH__
 
#include <type_traits>
 
#include "base/compiler.hh"

 
namespace gem5
{

class RefCounted
{
  private:
    // The reference count is mutable because one may want to
    // reference count a const pointer.  This really is OK because
    // const is about logical constness of the object not really about
    // strictly disallowing an object to change.
    mutable int count;
 
  private:
    // Don't allow a default copy constructor or copy operator on
    // these objects because the default operation will copy the
    // reference count as well and we certainly don't want that.
    RefCounted(const RefCounted &);
    RefCounted &operator=(const RefCounted &);
 
  public:
    RefCounted() : count(0) {}

    virtual ~RefCounted() {}

    void incref() const { ++count; }

    bool
    decref() const
    {
        return --count <= 0;
    }
};

template <class T>
class RefCountingPtr
{
  public:
    using PtrType = T*;
 
  protected:
    static constexpr auto TisConst = std::is_const_v<T>;
    using ConstT = typename std::conditional_t<TisConst,
            RefCountingPtr<T>,
            RefCountingPtr<typename std::add_const<T>::type>>;
    friend ConstT;
    using NonConstT = typename std::conditional_t<TisConst,
            RefCountingPtr<typename std::remove_const<T>::type>,
            RefCountingPtr<T>>;
    friend NonConstT;
    T *data;

    void
    copy(T *d)
    {
        data = d;
        if (data)
            data->incref();
    }

    GEM5_NO_INLINE void
    del()
    {
        if (data && data->decref()) {
            delete data;
        }
    }

    void
    set(T *d)
    {
        // Need to check if we're actually changing because otherwise
        // we could delete the last reference before adding the new
        // reference.
        if (data != d) {
            del();
            copy(d);
        }
    }
 
  public:
    RefCountingPtr() : data(0) {}

    RefCountingPtr(T *data) { copy(data); }

    RefCountingPtr(const RefCountingPtr &r) { copy(r.data); }

    RefCountingPtr(RefCountingPtr&& r)
    {
        data = r.data;
        r.data = nullptr;
    }
 
    template <bool B = TisConst>
    RefCountingPtr(const NonConstT &r) { copy(r.data); }

    ~RefCountingPtr() { del(); }
 
    // The following pointer access functions are const because they
    // don't actually change the pointer, though the user could change
    // what is pointed to.  This is analagous to a "Foo * const".

    T *operator->() const { return data; }

    T &operator*() const { return *data; }

    T *get() const { return data; }
 
    template <bool B = TisConst>
    operator RefCountingPtr<typename std::enable_if_t<!B, ConstT>>()
    {
        return RefCountingPtr<const T>(*this);
    }

    const RefCountingPtr &operator=(T *p) { set(p); return *this; }

    const RefCountingPtr &
    operator=(const RefCountingPtr &r)
    {
        return operator=(r.data);
    }

    const RefCountingPtr &
    operator=(RefCountingPtr&& r)
    {
        /* This happens regardless of whether the pointer is the same or not,
         * because of the move semantics, the rvalue needs to be 'destroyed'.
         */
        del();
        data = r.data;
        r.data = nullptr;
        return *this;
    }

    bool operator!() const { return data == 0; }

    operator bool() const { return data != 0; }
};

template<class T>
inline bool
operator==(const RefCountingPtr<T> &l, const RefCountingPtr<T> &r)
{
    return l.get() == r.get();
}

template<class T>
inline bool
operator==(const RefCountingPtr<T> &l, const T *r)
{
    return l.get() == r;
}

template<class T>
inline bool
operator==(const T *l, const RefCountingPtr<T> &r)
{
    return l == r.get();
}

template<class T>
inline bool
operator!=(const RefCountingPtr<T> &l, const RefCountingPtr<T> &r)
{
    return l.get() != r.get();
}

template<class T>
inline bool
operator!=(const RefCountingPtr<T> &l, const T *r)
{
    return l.get() != r;
}

template<class T>
inline bool
operator!=(const T *l, const RefCountingPtr<T> &r)
{
    return l != r.get();
}
 
} // namespace gem5
 
#endif // __BASE_REFCNT_HH__