CellPtr.h

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// -*- mode: c++; c-file-style: "linux"; c-basic-offset: 2; indent-tabs-mode: nil -*-
//
//  Copyright (C) 2020      Kuba Ober <kuba@bertec.com>
//
//  This program is free software; you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation; either version 2 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//
//  You should have received a copy of the GNU General Public License
//  along with this program; if not, write to the Free Software
//  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
//
//  SPDX-License-Identifier: GPL-2.0+
 
#ifndef CELLPTR_H
#define CELLPTR_H
 
#include <wx/debug.h>
#include <wx/log.h>
#include <cstddef>
#include <cstdint>
#include <cinttypes>
#include <memory>
#include <type_traits>
 
#define CELLPTR_CAST_TO_PTR 1
 
#ifndef CELLPTR_COUNT_INSTANCES
#define CELLPTR_COUNT_INSTANCES 0
#endif
 
#ifndef CELLPTR_LOG_REFS
#define CELLPTR_LOG_REFS 0
#endif
 
#ifndef CELLPTR_LOG_INSTANCES
#define CELLPTR_LOG_INSTANCES 0
#endif
 
#ifndef CELLPTR_LOG_METHOD
#define CELLPTR_LOG_METHOD wxLogDebug
#endif
 
class CellPtrBase;
 
class Observed
{
  class ControlBlock final
  {
    Observed *m_object = {};
    unsigned int m_refCount = 0;
    static size_t m_instanceCount;
 
  #if CELLPTR_LOG_REFS
    void LogConstruct(const Observed *) const;
    void LogRef(const CellPtrBase *) const;
    void LogDeref(const CellPtrBase *) const;
    void LogDestruct() const;
  #else
    void LogConstruct(const Observed *) const {}
    void LogRef(const CellPtrBase *) const {}
    void LogDeref(const CellPtrBase *) const {}
    void LogDestruct() const {}
  #endif
 
  public:
    explicit ControlBlock(Observed *object) : m_object(object)
    {
    #if CELLPTR_COUNT_INSTANCES
      ++ m_instanceCount;
    #endif
      LogConstruct(object);
      wxASSERT(object);
    }
    ~ControlBlock() {
    #if CELLPTR_COUNT_INSTANCES
      -- m_instanceCount;
    #endif
      LogDestruct();
    }
    ControlBlock(const ControlBlock &) = delete;
    void operator=(const ControlBlock &) = delete;
 
    void reset() noexcept { m_object = nullptr; }
    inline Observed *Get() const noexcept { return m_object; }
 
    ControlBlock *Ref(const CellPtrBase *cellptr)
    {
      LogRef(cellptr);
      ++m_refCount;
      return this;
    }
 
    bool Deref(const CellPtrBase *cellptr)
    {
      LogDeref(cellptr);
      wxASSERT(m_refCount >= 1);
      return --m_refCount;
    }
 
    static size_t GetLiveInstanceCount() { return m_instanceCount; }
  };
 
  static_assert(alignof(ControlBlock) >= 4, "Observed::ControlBlock doesn't have minimum viable alignment");
 
  class CellPtrImplPointer final
  {
    friend void swap(CellPtrImplPointer &a, CellPtrImplPointer &b) noexcept;
    uintptr_t m_ptr = {};
    enum Tag : uintptr_t {
      to_Observed = 0,
      to_ControlBlock = 1,
      to_CellPtrBase = 2,
      to_MASK = 3,
      to_MASK_OUT = uintptr_t(-intptr_t(to_MASK + 1)),
    };
  static uintptr_t ReprFor(Observed *ptr) noexcept
    { return reinterpret_cast<uintptr_t>(ptr) | to_Observed; }
  static uintptr_t ReprFor(ControlBlock *ptr) noexcept
    { return reinterpret_cast<uintptr_t>(ptr) | to_ControlBlock; }
  static uintptr_t ReprFor(CellPtrBase *ptr) noexcept
    { return reinterpret_cast<uintptr_t>(ptr) | to_CellPtrBase; }
  public:
    constexpr CellPtrImplPointer() noexcept {}
    constexpr CellPtrImplPointer(const CellPtrImplPointer &) noexcept = default;
    // cppcheck-suppress noExplicitConstructor
    constexpr CellPtrImplPointer(decltype(nullptr)) noexcept {}
    // cppcheck-suppress noExplicitConstructor
    CellPtrImplPointer(Observed *ptr) noexcept     : m_ptr(ReprFor(ptr)) {}
    // cppcheck-suppress noExplicitConstructor
    CellPtrImplPointer(ControlBlock *ptr) noexcept : m_ptr(ReprFor(ptr)) {}
    // cppcheck-suppress noExplicitConstructor
    CellPtrImplPointer(CellPtrBase *ptr) noexcept  : m_ptr(ReprFor(ptr)) {}
 
    constexpr CellPtrImplPointer &operator=(decltype(nullptr)) noexcept    { m_ptr = {};           return *this; }
    constexpr CellPtrImplPointer &operator=(CellPtrImplPointer o) noexcept { m_ptr = o.m_ptr;      return *this; }
    CellPtrImplPointer &operator=(Observed *ptr) noexcept                  { m_ptr = ReprFor(ptr); return *this; }
    CellPtrImplPointer &operator=(ControlBlock *ptr) noexcept              { m_ptr = ReprFor(ptr); return *this; }
    CellPtrImplPointer &operator=(CellPtrBase *ptr) noexcept               { m_ptr = ReprFor(ptr); return *this; }
 
    constexpr explicit inline operator bool() const noexcept { return m_ptr != 0; }
    constexpr inline bool HasObserved() const noexcept     { return (m_ptr & to_MASK) == to_Observed; }
    constexpr inline bool HasControlBlock() const noexcept { return (m_ptr & to_MASK) == to_ControlBlock; }
    constexpr inline bool HasCellPtrBase() const noexcept  { return (m_ptr & to_MASK) == to_CellPtrBase; }
    constexpr inline auto GetObserved() const noexcept     { static_assert((to_Observed & to_MASK_OUT) == 0, "");
                                                             return HasObserved()     ? reinterpret_cast<Observed *>    (m_ptr) : nullptr;               }
    constexpr inline auto GetControlBlock() const noexcept { return HasControlBlock() ? reinterpret_cast<ControlBlock *>(m_ptr & to_MASK_OUT) : nullptr; }
    constexpr inline auto GetCellPtrBase() const noexcept  { return HasCellPtrBase()  ? reinterpret_cast<CellPtrBase *> (m_ptr & to_MASK_OUT) : nullptr; }
 
    constexpr inline auto GetImpl() const noexcept { return m_ptr; }
    inline auto CastAsObserved() const noexcept     { return reinterpret_cast<Observed *>(m_ptr); }
    inline auto CastAsControlBlock() const noexcept { return reinterpret_cast<ControlBlock *>(m_ptr & to_MASK_OUT); }
  };
 
  friend void swap(CellPtrImplPointer &a, CellPtrImplPointer &b) noexcept;
  friend class CellPtrBase;
  static size_t m_instanceCount;
 
  CellPtrImplPointer m_ptr;
 
  Observed(const Observed &) = delete;
  void operator=(const Observed &) = delete;
  void OnEndOfLife() noexcept;
 
#if CELLPTR_LOG_REFS
  void LogRef(const CellPtrBase *) const;
  void LogDeref(const CellPtrBase *) const;
#else
  void LogRef(const CellPtrBase *) const {}
  void LogDeref(const CellPtrBase *) const {}
#endif
 
protected:
  Observed() noexcept
#if CELLPTR_COUNT_INSTANCES
  { ++ m_instanceCount; }
#else
  = default;
#endif
  ~Observed()
  {
    if (m_ptr) OnEndOfLife();
  #if CELLPTR_COUNT_INSTANCES
    -- m_instanceCount;
  #endif
  }
 
public:
  static size_t GetLiveInstanceCount() { return m_instanceCount; }
  static size_t GetLiveControlBlockInstanceCount() { return ControlBlock::GetLiveInstanceCount(); }
  bool IsNull() const { return !m_ptr.GetImpl(); }
  bool HasControlBlock() const { return m_ptr.GetControlBlock(); }
  bool HasOneCellPtr() const { return m_ptr.GetCellPtrBase(); }
};
 
inline void swap(Observed::CellPtrImplPointer &a, Observed::CellPtrImplPointer &b) noexcept
{ std::swap(a.m_ptr, b.m_ptr); }
 
class Cell;
class GroupCell;
 
class CellPtrBase
{
  using CellPtrImplPointer = Observed::CellPtrImplPointer;
  using ControlBlock = Observed::ControlBlock;
  static size_t m_instanceCount;
 
  mutable CellPtrImplPointer m_ptr;
 
  void Ref(Observed *obj);
 
  void Deref() noexcept;
 
  decltype(nullptr) DerefControlBlock() const noexcept;
 
#if CELLPTR_LOG_INSTANCES
  void LogConstruction(Observed *obj) const;
  void LogMove(const CellPtrBase &o) const;
  void LogAssignment(const CellPtrBase &o) const;
  void LogDestruction() const;
#else
  inline void LogConstruction(Observed *) const {}
  inline void LogMove(const CellPtrBase &) const {}
  inline void LogAssignment(const CellPtrBase &) const {}
  inline void LogDestruction() const {}
#endif
 
protected:
  explicit CellPtrBase(Observed *obj = nullptr) noexcept
  {
  #if CELLPTR_COUNT_INSTANCES
    ++m_instanceCount;
  #endif
    if (obj) Ref(obj);
    LogConstruction(obj);
  }
 
  CellPtrBase(const CellPtrBase &o) noexcept : CellPtrBase(o.base_get()) {}
 
  CellPtrBase(CellPtrBase &&o) noexcept
  {
  #if CELLPTR_COUNT_INSTANCES
    ++m_instanceCount;
  #endif
    LogMove(o);
    using namespace std;
 
    auto *thisObserved = m_ptr.GetObserved();
    if (thisObserved)
    {
      wxASSERT(thisObserved->m_ptr.GetCellPtrBase() == this);
      thisObserved->LogDeref(this);
      thisObserved->LogRef(&o);
      thisObserved->m_ptr = &o;
    }
 
    auto *otherObserved = o.m_ptr.GetObserved();
    if (otherObserved)
    {
      wxASSERT(otherObserved->m_ptr.GetCellPtrBase() == &o);
      otherObserved->LogDeref(&o);
      otherObserved->LogRef(this);
      otherObserved->m_ptr = this;
    }
 
    swap(m_ptr, o.m_ptr);
  }
 
  ~CellPtrBase() noexcept
  {
  #if CELLPTR_COUNT_INSTANCES
    --m_instanceCount;
  #endif
    LogDestruction();
    Deref();
  }
 
  CellPtrBase &operator=(const CellPtrBase &o) noexcept
  {
    base_reset(o.base_get());
    return *this;
  }
 
  CellPtrBase &operator=(CellPtrBase &&o) noexcept
  {
    LogAssignment(o);
    using namespace std;
    swap(m_ptr, o.m_ptr);
    return *this;
  }
 
  inline Observed *base_get() const noexcept
  {
    // Warning: This function is CRITICAL to the performance of wxMaxima
    // as a whole!
    //
    // The common hot path that iterates cells via the m_nextToDraw uses
    // this function and is intimately tied to its performance. Small
    // changes here can cause performance regressions - or small performance
    // improvements.
    //
    // If you change anything, do before- and after- measurements to verify
    // that whatever improvement you sought is in fact achieved. Changes that
    // don't measurably improve performance are discouraged.
 
    // The common path, meant to be hot: if we point directly at the observed object,
    // just return that. This is also where null is returned if the pointer is null.
    // `HasObserved()` is a simple bitmask test, and `CastAsObserved` is a binary
    // NO-OP.
 
    if (m_ptr.HasObserved())
      return m_ptr.CastAsObserved();
 
    // Otherwise, we must be pointing to a control block: get the pointed-to
    // observed from the control block. Since such use case is meant to be
    // rare, the overhead of pointer chasing (one extra layer of indirection)
    // is acceptable.
 
    auto *const observed = m_ptr.CastAsControlBlock()->Get();
    if (observed)
      return observed;
 
    // We have a control block, but the observed object is gone: we dereference
    // the zombie control block, to deallocate it as soon as possible, and we
    // reset ourselves to null. This happens only once per observed object, and
    // subsequent calls will go via the common path.
 
    return DerefControlBlock(); // returns null - allows a tail call optimization
  }
 
  void base_reset(Observed *obj = nullptr) noexcept;
 
public:
  template <typename U>
  static bool constexpr is_pointer() {
    return std::is_same<U, decltype(nullptr)>::value
           || (std::is_pointer<U>::value && std::is_convertible<U, Observed*>::value);
  }
 
  explicit operator bool() const noexcept { return base_get(); }
 
  inline void reset() noexcept { base_reset(); }
 
  auto cmpPointers(const CellPtrBase &o) const noexcept { return m_ptr.GetImpl() - o.m_ptr.GetImpl(); }
 
  auto cmpObjects(const CellPtrBase &o) const noexcept { return base_get() - o.base_get(); }
 
  auto cmpObjects(const Observed *o) const noexcept { return base_get() - o; }
 
  static size_t GetLiveInstanceCount() noexcept { return m_instanceCount; }
 
  bool IsNull() const { return !m_ptr.GetImpl(); }
  bool HasOneObserved() const { return m_ptr.GetObserved(); }
  bool HasControlBlock() const { return m_ptr.GetControlBlock(); }
};
 
static_assert(alignof(Observed) >= 4, "Observed doesn't have minimum viable alignment");
static_assert(alignof(CellPtrBase) >= 4, "CellPtrBase doesn't have minimum viable alignment");
 
template <typename T>
class CellPtr final : public CellPtrBase
{
  template <typename U>
  static bool constexpr is_pointer() {
    return std::is_same<U, decltype(nullptr)>::value
           || (std::is_pointer<U>::value && std::is_convertible<U, pointer>::value);
  }
public:
  using value_type = T;
  using pointer = T*;
  using const_pointer = const T*;
  using reference = T&;
 
  CellPtr() noexcept = default;
 
  // Observers
  //
  pointer get() const noexcept;
  inline reference operator*() const noexcept { return *get(); }
  inline pointer operator->() const noexcept { return get(); }
 
#if CELLPTR_CAST_TO_PTR
  operator pointer() const noexcept { return get(); }
#endif
 
  template <typename PtrT, typename std::enable_if<std::is_pointer<PtrT>::value, bool>::type = true>
  PtrT CastAs() const noexcept;
 
  // Operations with NULL and integers in general
  //
  explicit CellPtr(int) = delete;
  explicit CellPtr(void *) = delete;
 
  // Operations with nullptr_t
  //
  void reset() noexcept { base_reset(); }
  explicit CellPtr(decltype(nullptr)) noexcept {}
  CellPtr &operator=(decltype(nullptr)) noexcept { base_reset(); return *this; }
  bool operator==(decltype(nullptr)) const noexcept { return !bool(*this); }
  bool operator!=(decltype(nullptr)) const noexcept { return bool(*this); }
 
  // Operations with convertible-to-pointer types
  //
  template <typename U, typename std::enable_if<is_pointer<U>(), bool>::type = true>
  explicit CellPtr(U obj) noexcept : CellPtrBase(obj) {}
 
  template <typename U, typename std::enable_if<is_pointer<U>(), bool>::type = true>
  CellPtr &operator=(U obj) noexcept
  {
    base_reset(obj);
    return *this;
  }
 
  template <typename U, typename std::enable_if<is_pointer<U>(), bool>::type = true>
  void reset(U obj) noexcept
  { base_reset(obj); }
  // Operations with compatible CellPtrs
  //
  CellPtr(CellPtr &o) noexcept : CellPtrBase(o) {}
  CellPtr(CellPtr &&o) noexcept : CellPtrBase(std::move(o)) {}
  CellPtr &operator=(const CellPtr &o) noexcept { CellPtrBase::operator=(o); return *this; }
  CellPtr &operator=(CellPtr &&o) noexcept { CellPtrBase::operator=(std::move(o)); return *this; }
 
  template <typename U,
           typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, pointer>::value, bool>::type = true>
  // cppcheck-suppress noExplicitConstructor
  CellPtr(CellPtr<U> &&o) noexcept : CellPtrBase(o) {}
 
  template <typename U,
           typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, pointer>::value, bool>::type = true>
  // cppcheck-suppress noExplicitConstructor
  CellPtr(const CellPtr<U> &o) noexcept : CellPtrBase(o.get()) {}
 
  template <typename U,
           typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, pointer>::value, bool>::type = true>
  CellPtr &operator=(CellPtr<U> &&o) noexcept
  {
    CellPtrBase::operator=(o);
    return *this;
  }
  template <typename U,
           typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, pointer>::value, bool>::type = true>
  CellPtr &operator=(const CellPtr<U> &o) noexcept
  {
    CellPtrBase::operator=(o);
    return *this;
  }
 
#if !CELLPTR_CAST_TO_PTR
  template <typename U,
           typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, pointer>::value, bool>::type = true>
  bool operator==(const CellPtr<U> &ptr) const noexcept { return cmpControlBlocks(ptr) == 0; }
  template <typename U,
           typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, pointer>::value, bool>::type = true>
  bool operator!=(const CellPtr<U> &ptr) const noexcept { return cmpControlBlocks(ptr) != 0; }
  template <typename U,
           typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, pointer>::value, bool>::type = true>
  bool operator<(const CellPtr<U> &ptr) const noexcept { return cmpObjects(ptr) < 0; }
#endif
 
  // Operations with compatible unique_ptr
  //
  template <typename U, typename Del>
  explicit CellPtr(std::unique_ptr<U, Del> &&) = delete;
 
  template <typename U, typename Del,
           typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, pointer>::value, bool>::type = true>
  explicit CellPtr(const std::unique_ptr<U, Del> &ptr) noexcept : CellPtrBase(ptr.get()) {}
 
  template <typename U, typename Del>
  CellPtr &operator=(std::unique_ptr<U, Del> &&) = delete;
 
  template <typename U, typename Del,
           typename std::enable_if<std::is_convertible<typename std::add_pointer<U>::type, pointer>::value, bool>::type = true>
  CellPtr &operator=(const std::unique_ptr<U, Del> &o) noexcept
  { return *this = o.get(); }
};
 
//
 
template <typename T> typename
CellPtr<T>::pointer CellPtr<T>::get() const noexcept { return static_cast<pointer>(base_get()); }
 
template <>
CellPtr<GroupCell>::pointer CellPtr<GroupCell>::get() const noexcept;
 
//
 
template <typename T, typename U>
bool operator==(const CellPtr<T> &left, const CellPtr<U> &right) noexcept { return left.cmpPointers(right) == 0; }
 
#if !CELLPTR_CAST_TO_PTR
template <typename T, typename U,
         typename std::enable_if<CellPtrBase::is_pointer<U>(), bool>::type = true>
bool operator==(U left, const CellPtr<T> &right) noexcept { return right.cmpObjects(left) == 0; }
#endif
 
template <typename T, typename U,
         typename std::enable_if<CellPtrBase::is_pointer<U>(), bool>::type = true>
bool operator==(const CellPtr<T> &left, U right) noexcept { return left.cmpObjects(right) == 0; }
 
template <typename T, typename U>
bool operator!=(const CellPtr<T> &left, const CellPtr<U> &right) noexcept { return left.cmpPointers(right) != 0; }
 
#if !CELLPTR_CAST_TO_PTR
template <typename T, typename U,
         typename std::enable_if<CellPtrBase::is_pointer<U>(), bool>::type = true>
bool operator!=(U left, const CellPtr<T> &right) noexcept { return right.cmpObjects(left) != 0; }
#endif
 
template <typename T, typename U,
         typename std::enable_if<CellPtrBase::is_pointer<U>(), bool>::type = true>
bool operator!=(const CellPtr<T> &left, U right) noexcept { return left.cmpObjects(right) != 0; }
 
template <typename T, typename U>
bool operator<(const CellPtr<T> &left, const CellPtr<U> &right) noexcept { return left.cmpObjects(right) < 0; }
 
#if !CELLPTR_CAST_TO_PTR
template <typename T, typename U,
         typename std::enable_if<CellPtrBase::is_pointer<U>(), bool>::type = true>
bool operator<(U left, const CellPtr<T> &right) noexcept { return right.cmpObjects(left) > 0; }
#endif
 
template <typename T, typename U,
         typename std::enable_if<CellPtrBase::is_pointer<U>(), bool>::type = true>
bool operator<(const CellPtr<T> &left, U right) noexcept { return left.cmpObjects(right) < 0; }
 
//
 
template<typename Derived, typename Base>
std::unique_ptr<Derived> static_unique_ptr_cast(std::unique_ptr<Base>&& p) noexcept
{
  auto d = static_cast<Derived *>(p.release());
  return std::unique_ptr<Derived>(d);
  // Note: We don't move the deleter, since it's not special.
}
 
template<typename Derived, typename Base>
std::unique_ptr<Derived> dynamic_unique_ptr_cast(std::unique_ptr<Base>&& p) noexcept
{
  auto d = dynamic_cast<Derived *>(p.get());
  if (d)
    p.release();
  return std::unique_ptr<Derived>(d);
  // Note: We don't move the deleter, since it's not special.
}
 
#endif // CELLPTR_H