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// Copyright 2020 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef V8_HEAP_CPPGC_OBJECT_START_BITMAP_H_
#define V8_HEAP_CPPGC_OBJECT_START_BITMAP_H_
#include <limits.h>
#include <stdint.h>
#include <array>
#include "src/base/macros.h"
#include "src/heap/cppgc/globals.h"
namespace cppgc {
namespace internal {
class HeapObjectHeader;
// A bitmap for recording object starts. Objects have to be allocated at
// minimum granularity of kGranularity.
//
// Depends on internals such as:
// - kBlinkPageSize
// - kAllocationGranularity
class V8_EXPORT_PRIVATE ObjectStartBitmap {
public:
// Granularity of addresses added to the bitmap.
static constexpr size_t Granularity() { return kAllocationGranularity; }
// Maximum number of entries in the bitmap.
static constexpr size_t MaxEntries() {
return kReservedForBitmap * kBitsPerCell;
}
explicit inline ObjectStartBitmap(Address offset);
// Finds an object header based on a
// address_maybe_pointing_to_the_middle_of_object. Will search for an object
// start in decreasing address order.
inline HeapObjectHeader* FindHeader(
ConstAddress address_maybe_pointing_to_the_middle_of_object) const;
inline void SetBit(ConstAddress);
inline void ClearBit(ConstAddress);
inline bool CheckBit(ConstAddress) const;
// Iterates all object starts recorded in the bitmap.
//
// The callback is of type
// void(Address)
// and is passed the object start address as parameter.
template <typename Callback>
inline void Iterate(Callback) const;
// Clear the object start bitmap.
inline void Clear();
private:
static constexpr size_t kBitsPerCell = sizeof(uint8_t) * CHAR_BIT;
static constexpr size_t kCellMask = kBitsPerCell - 1;
static constexpr size_t kBitmapSize =
(kPageSize + ((kBitsPerCell * kAllocationGranularity) - 1)) /
(kBitsPerCell * kAllocationGranularity);
static constexpr size_t kReservedForBitmap =
((kBitmapSize + kAllocationMask) & ~kAllocationMask);
inline void ObjectStartIndexAndBit(ConstAddress, size_t*, size_t*) const;
Address offset_;
// The bitmap contains a bit for every kGranularity aligned address on a
// a NormalPage, i.e., for a page of size kBlinkPageSize.
std::array<uint8_t, kReservedForBitmap> object_start_bit_map_;
};
} // namespace internal
} // namespace cppgc
#endif // V8_HEAP_CPPGC_OBJECT_START_BITMAP_H_
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