chrome/common/partial_circular_buffer.h

   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.
  25 class 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_