BodyNodePtr.hpp

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 * Copyright (c) 2011-2021, The DART development contributors
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#ifndef DART_DYNAMICS_DETAIL_BODYNODEPTR_HPP_
#define DART_DYNAMICS_DETAIL_BODYNODEPTR_HPP_

#include <atomic>
#include <memory>
#include <mutex>

namespace dart {
namespace dynamics {

class Skeleton;

//==============================================================================
struct MutexedWeakSkeletonPtr
{
  std::mutex mMutex;
  std::weak_ptr<const Skeleton> mSkeleton;
};

//==============================================================================
class SkeletonRefCountingBase
{
public:
  template <class>
  friend class TemplateBodyNodePtr;
  template <class>
  friend class TemplateWeakBodyNodePtr;

  std::shared_ptr<Skeleton> getSkeleton();

  std::shared_ptr<const Skeleton> getSkeleton() const;

private:
  //--------------------------------------------------------------------------
  // Reference counting
  //--------------------------------------------------------------------------

  void incrementReferenceCount() const;

  void decrementReferenceCount() const;

protected:
  SkeletonRefCountingBase();

  std::weak_ptr<Skeleton> mSkeleton;

  mutable std::atomic<int> mReferenceCount;

  mutable std::shared_ptr<Skeleton> mReferenceSkeleton;

  std::shared_ptr<MutexedWeakSkeletonPtr> mLockedSkeleton;
};

template <class BodyNodeT>
class TemplateBodyNodePtr
{
public:
  TemplateBodyNodePtr() : mPtr(nullptr)
  {
  }

  TemplateBodyNodePtr(BodyNodeT* _ptr) : mPtr(nullptr)
  {
    set(_ptr);
  }

  TemplateBodyNodePtr(const TemplateBodyNodePtr& _bnp) : mPtr(nullptr)
  {
    set(_bnp.get());
  }

  template <class OtherBodyNodeT>
  TemplateBodyNodePtr(const TemplateBodyNodePtr<OtherBodyNodeT>& _bnp)
    : mPtr(nullptr)
  {
    set(_bnp.get());
  }

  ~TemplateBodyNodePtr()
  {
    set(nullptr);
  }

  TemplateBodyNodePtr& operator=(const TemplateBodyNodePtr& bnp)
  {
    set(bnp.get());
    return *this;
  }

  template <class OtherBodyNodeT>
  TemplateBodyNodePtr& operator=(
      const TemplateBodyNodePtr<OtherBodyNodeT>& _bnp)
  {
    set(_bnp.get());
    return *this;
  }

  TemplateBodyNodePtr& operator=(BodyNodeT* _ptr)
  {
    set(_ptr);
    return *this;
  }

  operator BodyNodeT*() const
  {
    return mPtr;
  }

  BodyNodeT& operator*() const
  {
    return *mPtr;
  }

  BodyNodeT* operator->() const
  {
    return mPtr;
  }

  BodyNodeT* get() const
  {
    return mPtr;
  }

  void set(BodyNodeT* _ptr)
  {
    if (mPtr == _ptr)
      return;

    if (nullptr != mPtr)
    {
      static_cast<const SkeletonRefCountingBase*>(mPtr)
          ->decrementReferenceCount();
    }

    if (nullptr != _ptr)
    {
      static_cast<const SkeletonRefCountingBase*>(_ptr)
          ->incrementReferenceCount();
    }

    mPtr = _ptr;
  }

private:
  BodyNodeT* mPtr;
};

template <class BodyNodeT>
class TemplateWeakBodyNodePtr
{
public:
  template <class>
  friend class TemplateWeakBodyNodePtr;

  TemplateWeakBodyNodePtr() : mPtr(nullptr)
  {
  }

  TemplateWeakBodyNodePtr(BodyNodeT* _ptr) : mPtr(nullptr)
  {
    set(_ptr);
  }

  template <class OtherBodyNodeT>
  TemplateWeakBodyNodePtr(
      const TemplateWeakBodyNodePtr<OtherBodyNodeT>& _weakPtr)
    : mPtr(nullptr)
  {
    set(_weakPtr);
  }

  TemplateWeakBodyNodePtr& operator=(BodyNodeT* _ptr)
  {
    set(_ptr);
    return *this;
  }

  template <class OtherBodyNodeT>
  TemplateWeakBodyNodePtr& operator=(
      const TemplateWeakBodyNodePtr<OtherBodyNodeT>& _weakPtr)
  {
    set(_weakPtr);
    return *this;
  }

  TemplateBodyNodePtr<BodyNodeT> lock() const
  {
    if (nullptr == mLocker)
      return nullptr;

    // We do not use the expired() function here, because we want to ensure that
    // the Skeleton's reference count remains up while we create the strong
    // BodyNodePtr that we're going to return.
    std::lock_guard<std::mutex> lock(mLocker->mMutex);
    std::shared_ptr<const Skeleton> skeleton = mLocker->mSkeleton.lock();
    if (nullptr == skeleton)
      return nullptr;

    return TemplateBodyNodePtr<BodyNodeT>(mPtr);
  }

  void set(BodyNodeT* _ptr)
  {
    mPtr = _ptr;

    if (nullptr == mPtr)
      mLocker = nullptr;
    else
      mLocker
          = static_cast<const SkeletonRefCountingBase*>(_ptr)->mLockedSkeleton;
  }

  template <class OtherBodyNodeT>
  void set(const TemplateWeakBodyNodePtr<OtherBodyNodeT>& _weakPtr)
  {
    if (nullptr == _weakPtr.mLocker)
    {
      set(nullptr);
      return;
    }

    std::lock_guard<std::mutex> lock(_weakPtr.mLocker->mMutex);
    std::shared_ptr<const Skeleton> skeleton
        = _weakPtr.mLocker->mSkeleton.lock();
    if (nullptr == skeleton)
    {
      set(nullptr);
      return;
    }

    set(_weakPtr.mPtr);
  }

  bool expired() const
  {
    if (nullptr == mLocker)
      return true;

    // It is okay for 'lock' to go "unused", because it is managed by RAII after
    // it has been initialized
    std::lock_guard<std::mutex> lock(mLocker->mMutex);
    std::shared_ptr<const Skeleton> skeleton = mLocker->mSkeleton.lock();
    if (nullptr == skeleton)
      return true;

    return false;
  }

private:
  BodyNodeT* mPtr;

  std::shared_ptr<MutexedWeakSkeletonPtr> mLocker;
};

} // namespace dynamics
} // namespace dart

#endif // DART_DYNAMICS_DETAIL_BODYNODEPTR_HPP_