refPtr.h

Go to the documentation of this file.

//
// Copyright 2016 Pixar
//
// Licensed under the terms set forth in the LICENSE.txt file available at
// https://openusd.org/license.
//
#ifndef PXR_BASE_TF_REF_PTR_H
#define PXR_BASE_TF_REF_PTR_H
 
 
#include "pxr/pxr.h"
 
#include "pxr/base/tf/diagnosticLite.h"
#include "pxr/base/tf/hash.h"
#include "pxr/base/tf/nullPtr.h"
#include "pxr/base/tf/refBase.h"
#include "pxr/base/tf/safeTypeCompare.h"
#include "pxr/base/tf/typeFunctions.h"
#include "pxr/base/tf/api.h"
 
#include "pxr/base/arch/hints.h"
 
 
#include <typeinfo>
#include <type_traits>
#include <cstddef>
 
PXR_NAMESPACE_OPEN_SCOPE
 
// Tf_SupportsUniqueChanged is a metafunction that may be specialized to return
// false for classes (and all derived classes) that *cannot* ever invoke unique
// changed listeners.
template <class T>
struct Tf_SupportsUniqueChanged {
    static const bool Value = true;
};
 
// Remnants are never able to support weak changed listeners.
class Tf_Remnant;
template <>
struct Tf_SupportsUniqueChanged<Tf_Remnant> {
    static const bool Value = false;
};
 
class TfWeakBase;
 
template <class T> class TfWeakPtr;
template <template <class> class X, class Y>
class TfWeakPtrFacade;
 
// Functions used for tracking.  Do not implement these.
inline void
Tf_RefPtrTracker_FirstRef(const void*, const TfRefBase *, const void*) { }
inline void
Tf_RefPtrTracker_LastRef(const void*, const TfRefBase *, const void*) { }
inline void
Tf_RefPtrTracker_New(const void*, const TfRefBase *, const void*) { }
inline void
Tf_RefPtrTracker_Delete(const void*, const TfRefBase *, const void*) { }
inline void
Tf_RefPtrTracker_Assign(const void*, const TfRefBase *,
                        const TfRefBase *, const void*) { }
 
// This code is used to increment and decrement ref counts in the common case.
// It may lock and invoke the unique changed listener, if the reference count
// becomes unique or non-unique.
struct Tf_RefPtr_UniqueChangedCounter {
    static inline void
    AddRef(TfRefBase const *refBase) {
        if (ARCH_UNLIKELY(!refBase)) {
            return;
        }
        const auto relaxed = std::memory_order_relaxed;
        // Read the current count value.
        std::atomic_int &counter = refBase->_GetRefCount();
        int prevCount = counter.load(relaxed);
        if (ARCH_UNLIKELY(prevCount < 0)) {
            // We need to invoke the unique changed listener if count goes from
            // -1 -> -2.  Try to CAS the value to one more count if it looks
            // like we won't take it from -1 -> -2.  If that works, we're done.
            // If not, we'll call an out-of-line function that handles the
            // locking part.
            if (prevCount != -1 && counter.
                compare_exchange_weak(prevCount, prevCount-1, relaxed)) {
                return;
            }
            _AddRefMaybeLocked(refBase, prevCount);
        }
        else {
            // Just bump the count.
            counter.fetch_add(1, relaxed);
        }
    }
 
    static inline bool
    RemoveRef(TfRefBase const* refBase) {
        if (ARCH_UNLIKELY(!refBase)) {
            return false;
        }
        const auto relaxed = std::memory_order_relaxed;
        const auto release = std::memory_order_release;
        // Read the current count value.
        std::atomic_int &counter = refBase->_GetRefCount();
        int prevCount = counter.load(relaxed);
        if (ARCH_UNLIKELY(prevCount < 0)) {
            // We need to invoke the unique changed listener if count goes from
            // -2 -> -1.  Try to CAS the value to one less count if it looks
            // like we won't take it from -2 -> -1.  If that works, we're done.
            // If not, we'll call an out-of-line function that handles the
            // locking part.
            if (prevCount != -2 && counter.
                compare_exchange_weak(prevCount, prevCount+1, release)) {
                return prevCount == -1;
            }
            return _RemoveRefMaybeLocked(refBase, prevCount);
        }
        else {
            // Just drop the count.
            return counter.fetch_sub(1, release) == 1;
        }
    }
 
    // Increment ptr's count if it is not zero.  Return true if done so
    // successfully, false if its count is zero.
    TF_API static bool
    AddRefIfNonzero(TfRefBase const *refBase);
    
    TF_API static void
    _AddRefMaybeLocked(TfRefBase const *refBase, int prevCount);
 
    TF_API static bool
    _RemoveRefMaybeLocked(TfRefBase const *refBase, int prevCount);
 
};
 
// This code is used to increment and decrement ref counts in the case where
// the object pointed to explicitly does not support unique changed listeners.
struct Tf_RefPtr_Counter {
    static inline void
    AddRef(TfRefBase const *refBase) {
        if (ARCH_UNLIKELY(!refBase)) {
            return;
        }
        refBase->_GetRefCount().fetch_add(1, std::memory_order_relaxed);
    }
 
    static inline bool
    RemoveRef(TfRefBase const *refBase) {
        if (ARCH_UNLIKELY(!refBase)) {
            return false;
        }
        return refBase->_GetRefCount()
            .fetch_sub(1, std::memory_order_release) == 1;
    }
 
    // Increment ptr's count if it is not zero.  Return true if done so
    // successfully, false if its count is zero.
    static inline bool
    AddRefIfNonzero(TfRefBase const *refBase) {
        if (ARCH_UNLIKELY(!refBase)) {
            return false;
        }
        auto &counter = refBase->_GetRefCount();
        int prevCount = counter.load(std::memory_order_relaxed);
        while (prevCount) {
            if (counter.compare_exchange_weak(prevCount, prevCount+1)) {
                return true;
            }
        }
        return false;
    }
};
 
// Helper to post a fatal error when a NULL Tf pointer is dereferenced.
[[noreturn]]
TF_API void
Tf_PostNullSmartPtrDereferenceFatalError(const TfCallContext &, const char *);
 
template <class T>
class TfRefPtr {
    // Select the counter based on whether T supports unique changed listeners.
    using _Counter = typename std::conditional<
        Tf_SupportsUniqueChanged<T>::Value &&
        !std::is_convertible<T*, TfSimpleRefBase*>::value,
        Tf_RefPtr_UniqueChangedCounter,
        Tf_RefPtr_Counter>::type;
 
    static constexpr T *_NullT = nullptr;
    
public:
    typedef T DataType;
 
    template <class U> struct Rebind {
        typedef TfRefPtr<U> Type;
    };
 
    TfRefPtr() : _refBase(nullptr) {
        Tf_RefPtrTracker_New(this, _refBase, _NullT);
    }
 
    TfRefPtr(TfRefPtr<T>&& p) : _refBase(p._refBase) {
        p._refBase = nullptr;
        Tf_RefPtrTracker_New(this, _refBase, _NullT);
        Tf_RefPtrTracker_Assign(&p, p._refBase, _refBase, _NullT);
    }
 
    TfRefPtr(const TfRefPtr<T>& p) : _refBase(p._refBase) {
        _AddRef();
        Tf_RefPtrTracker_New(this, _refBase, _NullT);
    }
 
    template <template <class> class X, class U>
    inline TfRefPtr(const TfWeakPtrFacade<X, U>& p,
                    typename std::enable_if<
                        std::is_convertible<U*, T*>::value
                    >::type * = 0);
 
#if defined(doxygen)
    friend inline TfRefPtr TfCreateRefPtr(T*);
#else
    template <class U>
    friend inline TfRefPtr<U> TfCreateRefPtr(U*);
#endif
 
    template <class U>
    explicit TfRefPtr(
        U* ptr, typename std::enable_if<
            std::is_convertible<U*, T*>::value>::type * = nullptr) :
        _refBase(ptr)
    {
        _AddRef();
        Tf_RefPtrTracker_New(this, _refBase, _NullT);
    }
 
    TfRefPtr(TfNullPtrType) : _refBase(nullptr)
    {
        Tf_RefPtrTracker_New(this, _refBase, _NullT);
    }
 
    TfRefPtr(std::nullptr_t) : _refBase(nullptr)
    {
        Tf_RefPtrTracker_New(this, _refBase, _NullT);
    }
 
    TfRefPtr<T>& operator=(const TfRefPtr<T>& p) {
        //
        // It is quite possible for
        //   ptr = TfNullPtr;
        // to delete the space that ptr actually lives in (this happens
        // when you use a circular reference to keep an object alive).
        // To avoid a crash, we have to ensure that deletion of the object
        // is the last thing done in the assignment; so we use some
        // local variables to help us out.
        //
 
        Tf_RefPtrTracker_Assign(this, p._refBase, _refBase, _NullT);
 
        const TfRefBase* tmp = _refBase;
        _refBase = p._refBase;
 
        p._AddRef();            // first!
        _RemoveRef(tmp);        // second!
        return *this;
    }
 
    TfRefPtr<T>& operator=(TfRefPtr<T>&& p) {
        // See comment in assignment operator.
        Tf_RefPtrTracker_Assign(this, p._refBase, _refBase, _NullT);
        Tf_RefPtrTracker_Assign(&p, nullptr, p._refBase, _NullT);
 
        const TfRefBase* tmp = _refBase;
        _refBase = p._refBase;
        p._refBase = nullptr;
        
        _RemoveRef(tmp);
        return *this;
    }
 
    ~TfRefPtr() {
        Tf_RefPtrTracker_Delete(this, _refBase, _NullT);
        _RemoveRef(_refBase);
    }
 
#if !defined(doxygen)
    template <class U>
#endif
    TfRefPtr(const TfRefPtr<U>& p) : _refBase(p._refBase) {
        static_assert(std::is_convertible<U*, T*>::value, "");
        _AddRef();
        Tf_RefPtrTracker_New(this, _refBase, _NullT);
    }
 
#if !defined(doxygen)
    template <class U>
#endif
    TfRefPtr(TfRefPtr<U>&& p) : _refBase(p._refBase) {
        static_assert(std::is_convertible<U*, T*>::value, "");
        p._refBase = nullptr;
        Tf_RefPtrTracker_New(this, _refBase, _NullT);
        Tf_RefPtrTracker_Assign(&p, p._refBase, _refBase, _NullT);
    }
 
#if !defined(doxygen)
    template <class U>
#endif
    TfRefPtr<T>& operator=(const TfRefPtr<U>& p) {
        static_assert(std::is_convertible<U*, T*>::value, "");
 
        Tf_RefPtrTracker_Assign(this, p._refBase, _refBase, _NullT);
        const TfRefBase* tmp = _refBase;
        _refBase = p._GetData();
        p._AddRef();            // first!
        _RemoveRef(tmp);        // second!
        return *this;
    }
 
#if !defined(doxygen)
    template <class U>
#endif
    TfRefPtr<T>& operator=(TfRefPtr<U>&& p) {
        static_assert(std::is_convertible<U*, T*>::value, "");
 
        Tf_RefPtrTracker_Assign(this, p._refBase, _refBase, _NullT);
        Tf_RefPtrTracker_Assign(&p, nullptr, p._refBase, _NullT);
        const TfRefBase* tmp = _refBase;
        _refBase = p._GetData();
        p._refBase = nullptr;
        _RemoveRef(tmp);
        return *this;
    }
 
#if !defined(doxygen)
    template <class U>
#endif
    auto operator==(const TfRefPtr<U>& p) const 
        -> decltype(std::declval<T *>() == std::declval<U *>(), bool()) {
        return _refBase == p._refBase;
    }
 
#if !defined(doxygen)
    template <class U>
#endif
    auto operator!=(const TfRefPtr<U>& p) const
        -> decltype(std::declval<T *>() != std::declval<U *>(), bool()) {
        return _refBase != p._refBase;
    }
 
#if !defined(doxygen)
    template <class U>
#endif
    auto operator<(const TfRefPtr<U>& p) const
        -> decltype(std::declval<T *>() < std::declval<U *>(), bool()) {
        return _refBase < p._refBase;
    }
 
#if !defined(doxygen)
    template <class U>
#endif
    auto operator>(const TfRefPtr<U>& p) const
        -> decltype(std::declval<T *>() > std::declval<U *>(), bool()) {
        return _refBase > p._refBase;
    }
 
#if !defined(doxygen)
    template <class U>
#endif
    auto operator<=(const TfRefPtr<U>& p) const
        -> decltype(std::declval<T *>() <= std::declval<U *>(), bool()) {
        return _refBase <= p._refBase;
    }
 
#if !defined(doxygen)
    template <class U>
#endif
    auto operator>=(const TfRefPtr<U>& p) const
        -> decltype(std::declval<T *>() >= std::declval<U *>(), bool()) {
        return _refBase >= p._refBase;
    }
 
    T* operator->() const {
        if (_refBase) {
            return static_cast<T*>(const_cast<TfRefBase*>(_refBase));
        }
        Tf_PostNullSmartPtrDereferenceFatalError(
            TF_CALL_CONTEXT, typeid(TfRefPtr).name());
    }
 
    T& operator *() const {
        return *operator->();
    }
 
#if !defined(doxygen)
    using UnspecifiedBoolType = const TfRefBase * (TfRefPtr::*);
#endif
 
    operator UnspecifiedBoolType() const {
        return _refBase ? &TfRefPtr::_refBase : nullptr;
    }
 
    bool operator !() const {
        return _refBase == nullptr;
    }
 
    void swap(TfRefPtr &other) {
        Tf_RefPtrTracker_Assign(this, other._refBase, _refBase, _NullT);
        Tf_RefPtrTracker_Assign(&other, _refBase, other._refBase, _NullT);
        std::swap(_refBase, other._refBase);
    }
 
    void Reset() {
        *this = TfNullPtr;
    }        
 
private:
    const TfRefBase* _refBase;
    
    template <class HashState, class U>
    friend inline void TfHashAppend(HashState &, const TfRefPtr<U>&);
    template <class U>
    friend inline size_t hash_value(const TfRefPtr<U>&);
 
    friend T *get_pointer(TfRefPtr const &p) {
        return static_cast<T *>(const_cast<TfRefBase *>(p._refBase));
    }
 
    // Used to distinguish construction in TfCreateRefPtr.
    class _CreateRefPtr { };
 
    // private constructor, used by TfCreateRefPtr()
    TfRefPtr(T* ptr, _CreateRefPtr /* unused */)
        : _refBase(ptr)
    {
        /* reference count is NOT bumped */
        Tf_RefPtrTracker_FirstRef(this, _refBase, _NullT);
        Tf_RefPtrTracker_New(this, _refBase, _NullT);
    }
 
    // Hide confusing internals of actual C++ definition (e.g. DataType)
    // for doxygen output:
 
#if defined(doxygen)
    // Sanitized for documentation:
    template <class D>
    friend inline TfRefPtr<D> TfDynamic_cast(const TfRefPtr<T>&);
#else
    template <class D, class B>
    friend TfRefPtr<typename D::DataType>
    TfDynamic_cast(const TfRefPtr<B>&);
 
    template <class D, class B>
    friend TfRefPtr<typename D::DataType>
    TfSafeDynamic_cast(const TfRefPtr<B>&);
#endif
 
#if defined(doxygen)
    // Sanitized for documentation:
    template <class D>
    friend inline TfRefPtr<D> TfStatic_cast(const TfRefPtr<T>&);
#else
    template <class D, class B>
    friend TfRefPtr<typename D::DataType>
    TfStatic_cast(const TfRefPtr<B>&);
 
#endif
 
#if defined(doxygen)
    // Sanitized for documentation:
    template <class D>
    friend inline TfRefPtr<D> TfConst_cast(const TfRefPtr<const D>&);
#else
    template <class D>
    friend TfRefPtr<typename D::DataType>
    TfConst_cast(const TfRefPtr<const typename D::DataType>&);
#endif
 
    T* _GetData() const {
        return static_cast<T*>(const_cast<TfRefBase*>(_refBase));
    }
 
 
    template <class U>
    friend const std::type_info& TfTypeid(const TfRefPtr<U>& ptr);
 
    void _AddRef() const {
        _Counter::AddRef(_refBase);
    }
 
    void _RemoveRef(const TfRefBase* ptr) const {
        if (_Counter::RemoveRef(ptr)) {
            // Synchronize with the release decrements of all other owners so
            // their prior accesses to *ptr happen-before its destruction.
            std::atomic_thread_fence(std::memory_order_acquire);
            Tf_RefPtrTracker_LastRef(this, ptr, _NullT);
            delete ptr;
        }
    }
 
#if ! defined(doxygen)
    // doxygen is very confused by this. It declares all TfRefPtrs
    // to be friends.
    template <class U> friend class TfRefPtr;
    template <class U> friend class TfWeakPtr;
    friend class Tf_Remnant;
 
    template <class U>
    friend TfRefPtr<U> TfCreateRefPtrFromProtectedWeakPtr(TfWeakPtr<U> const &);
#endif
    friend class TfWeakBase;
};
 
#if !defined(doxygen)
 
//
// nullptr comparisons
//
// These are provided to avoid ambiguous overloads due to
// TfWeakPtrFacade::Derived comparisons with TfRefPtr.
//
 
template <class T>
inline bool operator== (const TfRefPtr<T> &p, std::nullptr_t)
{
    return !p;
}
template <class T>
inline bool operator== (std::nullptr_t, const TfRefPtr<T> &p)
{
    return !p;
}
 
template <class T>
inline bool operator!= (const TfRefPtr<T> &p, std::nullptr_t)
{
    return !(p == nullptr);
}
template <class T>
inline bool operator!= (std::nullptr_t, const TfRefPtr<T> &p)
{
    return !(nullptr == p);
}
 
template <class T>
inline bool operator< (const TfRefPtr<T> &p, std::nullptr_t)
{
    return std::less<const TfRefBase *>()(get_pointer(p), nullptr);
}
template <class T>
inline bool operator< (std::nullptr_t, const TfRefPtr<T> &p)
{
    return std::less<const TfRefBase *>()(nullptr, get_pointer(p));
}
 
template <class T>
inline bool operator<= (const TfRefPtr<T> &p, std::nullptr_t)
{
    return !(nullptr < p);
}
template <class T>
inline bool operator<= (std::nullptr_t, const TfRefPtr<T> &p)
{
    return !(p < nullptr);
}
 
template <class T>
inline bool operator> (const TfRefPtr<T> &p, std::nullptr_t)
{
    return nullptr < p;
}
template <class T>
inline bool operator> (std::nullptr_t, const TfRefPtr<T> &p)
{
    return p < nullptr;
}
 
template <class T>
inline bool operator>= (const TfRefPtr<T> &p, std::nullptr_t)
{
    return !(p < nullptr);
}
template <class T>
inline bool operator>= (std::nullptr_t, const TfRefPtr<T> &p)
{
    return !(nullptr < p);
}
 
 
template <typename T>
inline TfRefPtr<T> TfCreateRefPtr(T* ptr) {
    return TfRefPtr<T>(ptr, typename TfRefPtr<T>::_CreateRefPtr());
}
 
template <class T>
const std::type_info&
TfTypeid(const TfRefPtr<T>& ptr)
{
    if (ARCH_UNLIKELY(!ptr._refBase))
        TF_FATAL_ERROR("called TfTypeid on NULL TfRefPtr");
 
    return typeid(*ptr._GetData());
}
 
template <class D, class T>
inline
TfRefPtr<typename D::DataType>
TfDynamic_cast(const TfRefPtr<T>& ptr)
{
    typedef TfRefPtr<typename D::DataType> RefPtr;
    return RefPtr(dynamic_cast<typename D::DataType*>(ptr._GetData()));
}
 
template <class D, class T>
inline
TfRefPtr<typename D::DataType>
TfSafeDynamic_cast(const TfRefPtr<T>& ptr)
{
    typedef TfRefPtr<typename D::DataType> RefPtr;
    return RefPtr(TfSafeDynamic_cast<typename D::DataType*>(ptr._GetData()));
}
 
template <class D, class T>
inline
TfRefPtr<typename D::DataType>
TfStatic_cast(const TfRefPtr<T>& ptr)
{
    typedef TfRefPtr<typename D::DataType> RefPtr;
    return RefPtr(static_cast<typename D::DataType*>(ptr._GetData()));
}
 
template <class T>
inline
TfRefPtr<typename T::DataType>
TfConst_cast(const TfRefPtr<const typename T::DataType>& ptr)
{
    // this ugly cast allows TfConst_cast to work without requiring
    // a definition for T.
    typedef TfRefPtr<typename T::DataType> NonConstRefPtr;
    return *((NonConstRefPtr*)(&ptr));
}
 
// Specialization: prevent construction of a TfRefPtr<TfRefBase>.
 
template <>
class TfRefPtr<TfRefBase> {
private:
    TfRefPtr() = delete;
};
 
template <>
class TfRefPtr<const TfRefBase> {
private:
    TfRefPtr() = delete;
};
 
template <class T>
struct TfTypeFunctions<TfRefPtr<T> > {
    static T* GetRawPtr(const TfRefPtr<T>& t) {
        return t.operator-> ();
    }
 
    static TfRefPtr<T> ConstructFromRawPtr(T* ptr) {
        return TfRefPtr<T>(ptr);
    }
    
    static bool IsNull(const TfRefPtr<T>& t) {
        return !t;
    }
 
    static void Class_Object_MUST_Be_Passed_By_Address() { }
    static void Class_Object_MUST_Not_Be_Const() { }
};
 
template <class T>
struct TfTypeFunctions<TfRefPtr<const T> > {
    static const T* GetRawPtr(const TfRefPtr<const T>& t) {
        return t.operator-> ();
    }
 
    static TfRefPtr<const T> ConstructFromRawPtr(T* ptr) {
        return TfRefPtr<const T>(ptr);
    }
 
    static bool IsNull(const TfRefPtr<const T>& t) {
        return !t;
    }
 
    static void Class_Object_MUST_Be_Passed_By_Address() { }
};
 
#endif
 
#if !defined(doxygen)
 
template <class T>
inline void
swap(TfRefPtr<T>& lhs, TfRefPtr<T>& rhs)
{
    lhs.swap(rhs);
}
 
template <class T>
inline size_t
hash_value(const TfRefPtr<T>& ptr)
{
    return TfHash()(ptr);
}
 
template <class HashState, class T>
inline void
TfHashAppend(HashState &h, const TfRefPtr<T> &ptr)
{
    h.Append(get_pointer(ptr));
}
 
#endif // !doxygen
 
#define TF_SUPPORTS_REFPTR(T) std::is_base_of_v<TfRefBase, T>
 
PXR_NAMESPACE_CLOSE_SCOPE
 
#endif // PXR_BASE_TF_REF_PTR_H