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// Copyright 2016 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_ZONE_ZONE_SEGMENT_H_
#define V8_ZONE_ZONE_SEGMENT_H_
#include "src/init/v8.h"
// Segments represent chunks of memory: They have starting address
// (encoded in the this pointer) and a size in bytes. Segments are
// chained together forming a LIFO structure with the newest segment
// available as segment_head_. Segments are allocated using malloc()
// and de-allocated using free().
namespace v8 {
namespace internal {
// Forward declarations.
class AccountingAllocator;
class Zone;
class Segment {
public:
Zone* zone() const { return zone_; }
void set_zone(Zone* const zone) { zone_ = zone; }
Segment* next() const { return next_; }
void set_next(Segment* const next) { next_ = next; }
// {total_size} returns the allocated size including the bookkeeping bytes of
// the {Segment}.
size_t total_size() const { return size_; }
// {capacity} returns the number of storage bytes in this {Segment}, i.e.
// {end() - start()}.
size_t capacity() const { return size_ - sizeof(Segment); }
Address start() const { return address(sizeof(Segment)); }
Address end() const { return address(size_); }
// Zap the contents of the segment (but not the header).
void ZapContents();
// Zaps the header and makes the segment unusable this way.
void ZapHeader();
private:
// Segments are only created by the AccountingAllocator.
friend class AccountingAllocator;
explicit Segment(size_t size) : size_(size) {}
#ifdef DEBUG
// Constant byte value used for zapping dead memory in debug mode.
static const unsigned char kZapDeadByte = 0xcd;
#endif
// Computes the address of the nth byte in this segment.
Address address(size_t n) const {
return reinterpret_cast<Address>(this) + n;
}
Zone* zone_ = nullptr;
Segment* next_ = nullptr;
const size_t size_;
};
} // namespace internal
} // namespace v8
#endif // V8_ZONE_ZONE_SEGMENT_H_
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