1// Copyright 2013 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#ifndef CHROME_COMMON_PARTIAL_CIRCULAR_BUFFER_H_
6#define CHROME_COMMON_PARTIAL_CIRCULAR_BUFFER_H_
7
8#include "base/basictypes.h"
9#include "base/gtest_prod_util.h"
10
11// A wrapper around a memory buffer that allows circular read and write with a
12// selectable wrapping position. Buffer layout (after wrap; H is header):
13// -----------------------------------------------------------
14// | H | Beginning           | End           | Middle        |
15// -----------------------------------------------------------
16//  ^---- Non-wrapping -----^ ^--------- Wrapping ----------^
17// The non-wrapping part is never overwritten. The wrapping part will be
18// circular. The very first part is the header (see the BufferData struct
19// below). It consists of the following information:
20// - Length written to the buffer (not including header).
21// - Wrapping position.
22// - End position of buffer. (If the last byte is at x, this will be x + 1.)
23// Users of wrappers around the same underlying buffer must ensure that writing
24// is finished before reading is started.
25class PartialCircularBuffer {
26 public:
27  // Use for reading. |buffer_size| is in bytes and must be larger than the
28  // header size (see above).
29  PartialCircularBuffer(void* buffer, uint32 buffer_size);
30
31  // Use for writing. |buffer_size| is in bytes and must be larger than the
32  // header size (see above). If |append| is true, the header data is not reset
33  // and writing will continue were left off, |wrap_position| is then ignored.
34  PartialCircularBuffer(void* buffer,
35                        uint32 buffer_size,
36                        uint32 wrap_position,
37                        bool append);
38
39  uint32 Read(void* buffer, uint32 buffer_size);
40  void Write(const void* buffer, uint32 buffer_size);
41
42 private:
43  friend class PartialCircularBufferTest;
44
45#pragma pack(push)
46#pragma pack(4)
47  struct BufferData {
48    uint32 total_written;
49    uint32 wrap_position;
50    uint32 end_position;
51    uint8 data[1];
52  };
53#pragma pack(pop)
54
55  void DoWrite(void* dest, const void* src, uint32 num);
56
57  // Used for reading and writing.
58  BufferData* buffer_data_;
59  uint32 memory_buffer_size_;
60  uint32 data_size_;
61  uint32 position_;
62
63  // Used for reading.
64  uint32 total_read_;
65};
66
67#endif  // CHROME_COMMON_PARTIAL_CIRCULAR_BUFFER_H_
68