text: /*
   * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
   *
   * SPDX-License-Identifier: BSD-2-Clause
   */
  
  #pragma once
  
  #include <AK/FixedArray.h>
  #include <AK/HashTable.h>
  #include <AK/IntrusiveList.h>
  #include <AK/RefCounted.h>
  #include <AK/RefPtr.h>
  #include <AK/Vector.h>
  #include <AK/Weakable.h>
  #include <Kernel/Forward.h>
  #include <Kernel/Mutex.h>
  #include <Kernel/VM/Region.h>
  
  namespace Kernel {
  
  class VMObjectDeletedHandler {
  public:
      virtual ~VMObjectDeletedHandler() = default;
      virtual void vmobject_deleted(VMObject&) = 0;
  };
  
  class VMObject : public RefCounted<VMObject>
      , public Weakable<VMObject> {
      friend class MemoryManager;
      friend class Region;
  
  public:
      virtual ~VMObject();
  
      virtual RefPtr<VMObject> try_clone() = 0;
  
      virtual bool is_anonymous() const { return false; }
      virtual bool is_inode() const { return false; }
      virtual bool is_shared_inode() const { return false; }
      virtual bool is_private_inode() const { return false; }
      virtual bool is_contiguous() const { return false; }
  
      size_t page_count() const { return m_physical_pages.size(); }
      Span<RefPtr<PhysicalPage> const> physical_pages() const { return m_physical_pages.span(); }
      Span<RefPtr<PhysicalPage>> physical_pages() { return m_physical_pages.span(); }
  
      size_t size() const { return m_physical_pages.size() * PAGE_SIZE; }
  
      virtual StringView class_name() const = 0;
  
      ALWAYS_INLINE void add_region(Region& region)
      {
          ScopedSpinLock locker(m_lock);
          m_regions_count++;
          m_regions.append(region);
      }
  
      ALWAYS_INLINE void remove_region(Region& region)
      {
          ScopedSpinLock locker(m_lock);
          m_regions_count--;
          m_regions.remove(region);
      }
  
      ALWAYS_INLINE bool is_shared_by_multiple_regions() const { return m_regions_count > 1; }
  
      void register_on_deleted_handler(VMObjectDeletedHandler& handler)
      {
          m_on_deleted.set(&handler);
      }
      void unregister_on_deleted_handler(VMObjectDeletedHandler& handler)
      {
          m_on_deleted.remove(&handler);
      }
  
  protected:
      explicit VMObject(size_t);
      explicit VMObject(VMObject const&);
  
      template<typename Callback>
      void for_each_region(Callback);
  
      IntrusiveListNode<VMObject> m_list_node;
      FixedArray<RefPtr<PhysicalPage>> m_physical_pages;
  
      mutable RecursiveSpinLock m_lock;
  
  private:
      VMObject& operator=(VMObject const&) = delete;
      VMObject& operator=(VMObject&&) = delete;
      VMObject(VMObject&&) = delete;
  
      Atomic<u32, AK::MemoryOrder::memory_order_relaxed> m_regions_count { 0 };
      HashTable<VMObjectDeletedHandler*> m_on_deleted;
      SpinLock<u8> m_on_deleted_lock;
  
      Region::ListInVMObject m_regions;
  
  public:
      using List = IntrusiveList<VMObject, RawPtr<VMObject>, &VMObject::m_list_node>;
  };
  
  template<typename Callback>
  inline void VMObject::for_each_region(Callback callback)
  {
      ScopedSpinLock lock(m_lock);
      for (auto& region : m_regions) {
          callback(region);
      }
  }
  
  inline PhysicalPage const* Region::physical_page(size_t index) const
  {
      VERIFY(index < page_count());
      return vmobject().physical_pages()[first_page_index() + index];
  }
  
  inline RefPtr<PhysicalPage>& Region::physical_page_slot(size_t index)
  {
      VERIFY(index < page_count());
      return vmobject().physical_pages()[first_page_index() + index];
  }
  
  }
  