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// Copyright 2013 The Chromium 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 CHROME_COMMON_PARTIAL_CIRCULAR_BUFFER_H_
#define CHROME_COMMON_PARTIAL_CIRCULAR_BUFFER_H_
#include "base/basictypes.h"
#include "base/gtest_prod_util.h"
// A wrapper around a memory buffer that allows circular read and write with a
// selectable wrapping position. Buffer layout (after wrap; H is header):
// -----------------------------------------------------------
// | H | Beginning | End | Middle |
// -----------------------------------------------------------
// ^---- Non-wrapping -----^ ^--------- Wrapping ----------^
// The non-wrapping part is never overwritten. The wrapping part will be
// circular. The very first part is the header (see the BufferData struct
// below). It consists of the following information:
// - Length written to the buffer (not including header).
// - Wrapping position.
// - End position of buffer. (If the last byte is at x, this will be x + 1.)
// Users of wrappers around the same underlying buffer must ensure that writing
// is finished before reading is started.
class PartialCircularBuffer {
public:
// Use for reading. |buffer_size| is in bytes and must be larger than the
// header size (see above).
PartialCircularBuffer(void* buffer, uint32 buffer_size);
// Use for writing. |buffer_size| is in bytes and must be larger than the
// header size (see above). If |append| is true, the header data is not reset
// and writing will continue were left off, |wrap_position| is then ignored.
PartialCircularBuffer(void* buffer,
uint32 buffer_size,
uint32 wrap_position,
bool append);
uint32 Read(void* buffer, uint32 buffer_size);
void Write(const void* buffer, uint32 buffer_size);
private:
friend class PartialCircularBufferTest;
#pragma pack(push)
#pragma pack(4)
struct BufferData {
uint32 total_written;
uint32 wrap_position;
uint32 end_position;
uint8 data[1];
};
#pragma pack(pop)
void DoWrite(void* dest, const void* src, uint32 num);
// Used for reading and writing.
BufferData* buffer_data_;
uint32 memory_buffer_size_;
uint32 data_size_;
uint32 position_;
// Used for reading.
uint32 total_read_;
};
#endif // CHROME_COMMON_PARTIAL_CIRCULAR_BUFFER_H_
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