chromium/media/base/seekable_buffer.h

// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// SeekableBuffer to support backward and forward seeking in a buffer for
// reading a media data source.
//
// In order to support backward and forward seeking, this class buffers data in
// both backward and forward directions, the current read position can be reset
// to anywhere in the buffered data.
//
// The amount of data buffered is regulated by two variables at construction,
// |backward_capacity| and |forward_capacity|.
//
// In the case of reading and seeking forward, the current read position
// advances and there will be more data in the backward direction. If backward
// bytes exceeds |backward_capacity|, the exceeding bytes are evicted and thus
// backward_bytes() will always be less than or equal to |backward_capacity|.
// The eviction will be caused by Read() and Seek() in the forward direction and
// is done internally when the mentioned criteria is fulfilled.
//
// In the case of appending data to the buffer, there is an advisory limit of
// how many bytes can be kept in the forward direction, regulated by
// |forward_capacity|. The append operation (by calling Append()) that caused
// forward bytes to exceed |forward_capacity| will have a return value that
// advises a halt of append operation, further append operations are allowed but
// are not advised. Since this class is used as a backend buffer for caching
// media files downloaded from network we cannot afford losing data, we can
// only advise a halt of further writing to this buffer.
// This class is not inherently thread-safe. Concurrent access must be
// externally serialized.

#ifndef MEDIA_BASE_SEEKABLE_BUFFER_H_
#define MEDIA_BASE_SEEKABLE_BUFFER_H_

#include <stdint.h>

#include <list>

#include "base/memory/scoped_refptr.h"
#include "base/time/time.h"
#include "media/base/media_export.h"

namespace media {

class DataBuffer;

class MEDIA_EXPORT SeekableBuffer { … };

}  // namespace media

#endif  // MEDIA_BASE_SEEKABLE_BUFFER_H_