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/*
* Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#pragma once
#include <AK/IntrusiveList.h>
#include <AK/Types.h>
#include <LibJS/Forward.h>
#include <LibJS/Heap/Cell.h>
namespace JS {
class HeapBlock {
AK_MAKE_NONCOPYABLE(HeapBlock);
AK_MAKE_NONMOVABLE(HeapBlock);
public:
static constexpr size_t block_size = 16 * KiB;
static NonnullOwnPtr<HeapBlock> create_with_cell_size(Heap&, size_t);
void operator delete(void*);
size_t cell_size() const { return m_cell_size; }
size_t cell_count() const { return (block_size - sizeof(HeapBlock)) / m_cell_size; }
bool is_full() const { return !has_lazy_freelist() && !m_freelist; }
ALWAYS_INLINE Cell* allocate()
{
if (m_freelist) {
VERIFY(is_valid_cell_pointer(m_freelist));
return exchange(m_freelist, m_freelist->next);
}
if (has_lazy_freelist())
return cell(m_next_lazy_freelist_index++);
return nullptr;
}
void deallocate(Cell*);
template<typename Callback>
void for_each_cell(Callback callback)
{
auto end = has_lazy_freelist() ? m_next_lazy_freelist_index : cell_count();
for (size_t i = 0; i < end; ++i)
callback(cell(i));
}
Heap& heap() { return m_heap; }
static HeapBlock* from_cell(const Cell* cell)
{
return reinterpret_cast<HeapBlock*>((FlatPtr)cell & ~(block_size - 1));
}
Cell* cell_from_possible_pointer(FlatPtr pointer)
{
if (pointer < reinterpret_cast<FlatPtr>(m_storage))
return nullptr;
size_t cell_index = (pointer - reinterpret_cast<FlatPtr>(m_storage)) / m_cell_size;
auto end = has_lazy_freelist() ? m_next_lazy_freelist_index : cell_count();
if (cell_index >= end)
return nullptr;
return cell(cell_index);
}
bool is_valid_cell_pointer(const Cell* cell)
{
return cell_from_possible_pointer((FlatPtr)cell);
}
IntrusiveListNode<HeapBlock> m_list_node;
private:
HeapBlock(Heap&, size_t cell_size);
bool has_lazy_freelist() const { return m_next_lazy_freelist_index < cell_count(); }
struct FreelistEntry final : public Cell {
FreelistEntry* next { nullptr };
virtual const char* class_name() const override { return "FreelistEntry"; }
};
Cell* cell(size_t index)
{
return reinterpret_cast<Cell*>(&m_storage[index * cell_size()]);
}
FreelistEntry* init_freelist_entry(size_t index)
{
return new (&m_storage[index * cell_size()]) FreelistEntry();
}
Heap& m_heap;
size_t m_cell_size { 0 };
size_t m_next_lazy_freelist_index { 0 };
FreelistEntry* m_freelist { nullptr };
alignas(Cell) u8 m_storage[];
};
}
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