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#ifndef INTRUSIVE_PTR_H
#define INTRUSIVE_PTR_H
#include <utility>
#include "atomic.h"
#include "opthelpers.h"
namespace al {
template<typename T>
class intrusive_ref {
std::atomic<unsigned int> mRef{1u};
public:
unsigned int add_ref() noexcept { return IncrementRef(mRef); }
unsigned int dec_ref() noexcept
{
auto ref = DecrementRef(mRef);
if(ref == 0) UNLIKELY
delete static_cast<T*>(this);
return ref;
}
/**
* Release only if doing so would not bring the object to 0 references and
* delete it. Returns false if the object could not be released.
*
* NOTE: The caller is responsible for handling a failed release, as it
* means the object has no other references and needs to be be deleted
* somehow.
*/
bool releaseIfNoDelete() noexcept
{
auto val = mRef.load(std::memory_order_acquire);
while(val > 1 && !mRef.compare_exchange_strong(val, val-1, std::memory_order_acq_rel))
{
/* val was updated with the current value on failure, so just try
* again.
*/
}
return val >= 2;
}
};
template<typename T>
class intrusive_ptr {
T *mPtr{nullptr};
public:
intrusive_ptr() noexcept = default;
intrusive_ptr(const intrusive_ptr &rhs) noexcept : mPtr{rhs.mPtr}
{ if(mPtr) mPtr->add_ref(); }
intrusive_ptr(intrusive_ptr&& rhs) noexcept : mPtr{rhs.mPtr}
{ rhs.mPtr = nullptr; }
intrusive_ptr(std::nullptr_t) noexcept { }
explicit intrusive_ptr(T *ptr) noexcept : mPtr{ptr} { }
~intrusive_ptr() { if(mPtr) mPtr->dec_ref(); }
intrusive_ptr& operator=(const intrusive_ptr &rhs) noexcept
{
static_assert(noexcept(std::declval<T*>()->dec_ref()), "dec_ref must be noexcept");
if(rhs.mPtr) rhs.mPtr->add_ref();
if(mPtr) mPtr->dec_ref();
mPtr = rhs.mPtr;
return *this;
}
intrusive_ptr& operator=(intrusive_ptr&& rhs) noexcept
{
if(&rhs != this) LIKELY
{
if(mPtr) mPtr->dec_ref();
mPtr = std::exchange(rhs.mPtr, nullptr);
}
return *this;
}
explicit operator bool() const noexcept { return mPtr != nullptr; }
T& operator*() const noexcept { return *mPtr; }
T* operator->() const noexcept { return mPtr; }
T* get() const noexcept { return mPtr; }
void reset(T *ptr=nullptr) noexcept
{
if(mPtr)
mPtr->dec_ref();
mPtr = ptr;
}
T* release() noexcept { return std::exchange(mPtr, nullptr); }
void swap(intrusive_ptr &rhs) noexcept { std::swap(mPtr, rhs.mPtr); }
void swap(intrusive_ptr&& rhs) noexcept { std::swap(mPtr, rhs.mPtr); }
};
#define AL_DECL_OP(op) \
template<typename T> \
inline bool operator op(const intrusive_ptr<T> &lhs, const T *rhs) noexcept \
{ return lhs.get() op rhs; } \
template<typename T> \
inline bool operator op(const T *lhs, const intrusive_ptr<T> &rhs) noexcept \
{ return lhs op rhs.get(); }
AL_DECL_OP(==)
AL_DECL_OP(!=)
AL_DECL_OP(<=)
AL_DECL_OP(>=)
AL_DECL_OP(<)
AL_DECL_OP(>)
#undef AL_DECL_OP
} // namespace al
#endif /* INTRUSIVE_PTR_H */
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