"Chunked" MemoryStream
Я ищу реализацию MemoryStream, которая не выделяет память как один большой блок, а скорее набор кусков. Я хочу хранить несколько ГБ данных в памяти (64 бит) и избегать ограничения фрагментации памяти.
Ответы
Ответ 1
Вам нужно сначала определить, является ли проблема фрагментацией виртуального адреса.
Если вы находитесь на 64-битной машине (которую вы, кажется, указываете на вас), я серьезно сомневаюсь. Каждый 64-битный процесс имеет почти все доступное 64-битное пространство виртуальной памяти, и единственное беспокойство - фрагментация виртуального адресного пространства, а не фрагментация физической памяти (о чем должна беспокоиться операционная система). Диспетчер памяти ОС уже загружает память под обложки. В обозримом будущем вы не закончите виртуальное адресное пространство до того, как закончите физическую память. Это вряд ли изменится, прежде чем мы оба выйдем на пенсию.
Если у вас есть 32-разрядное адресное пространство, то выделение смежных больших блоков памяти в графе GB вы столкнетесь с проблемой фрагментации довольно быстро. В CLR отсутствует поток памяти, распределяющий память. В ASP.NET(по другим причинам) есть один элемент под обложками, но он недоступен. Если вы должны путешествовать по этому пути, вам, вероятно, лучше написать один из вас, потому что шаблон использования вашего приложения вряд ли будет похож на многие другие, и попытка поместить ваши данные в 32-битное адресное пространство, скорее всего, станет вашим основным узким местом.
Я настоятельно рекомендую использовать 64-битный процесс, если вы манипулируете GBs данных. Он будет выполнять гораздо лучшую работу, чем ручные решения для 32-разрядной фрагментации адресного пространства, независимо от того, как вы находитесь.
Ответ 2
Что-то вроде этого:
class ChunkedMemoryStream : Stream
{
private readonly List<byte[]> _chunks = new List<byte[]>();
private int _positionChunk;
private int _positionOffset;
private long _position;
public override bool CanRead
{
get { return true; }
}
public override bool CanSeek
{
get { return true; }
}
public override bool CanWrite
{
get { return true; }
}
public override void Flush() { }
public override long Length
{
get { return _chunks.Sum(c => c.Length); }
}
public override long Position
{
get
{
return _position;
}
set
{
_position = value;
_positionChunk = 0;
while (_positionOffset != 0)
{
if (_positionChunk >= _chunks.Count)
throw new OverflowException();
if (_positionOffset < _chunks[_positionChunk].Length)
return;
_positionOffset -= _chunks[_positionChunk].Length;
_positionChunk++;
}
}
}
public override int Read(byte[] buffer, int offset, int count)
{
int result = 0;
while ((count != 0) && (_positionChunk != _chunks.Count))
{
int fromChunk = Math.Min(count, _chunks[_positionChunk].Length - _positionOffset);
if (fromChunk != 0)
{
Array.Copy(_chunks[_positionChunk], _positionOffset, buffer, offset, fromChunk);
offset += fromChunk;
count -= fromChunk;
result += fromChunk;
_position += fromChunk;
}
_positionOffset = 0;
_positionChunk++;
}
return result;
}
public override long Seek(long offset, SeekOrigin origin)
{
long newPos = 0;
switch (origin)
{
case SeekOrigin.Begin:
newPos = offset;
break;
case SeekOrigin.Current:
newPos = Position + offset;
break;
case SeekOrigin.End:
newPos = Length - offset;
break;
}
Position = Math.Max(0, Math.Min(newPos, Length));
return newPos;
}
public override void SetLength(long value)
{
throw new NotImplementedException();
}
public override void Write(byte[] buffer, int offset, int count)
{
while ((count != 0) && (_positionChunk != _chunks.Count))
{
int toChunk = Math.Min(count, _chunks[_positionChunk].Length - _positionOffset);
if (toChunk != 0)
{
Array.Copy(buffer, offset, _chunks[_positionChunk], _positionOffset, toChunk);
offset += toChunk;
count -= toChunk;
_position += toChunk;
}
_positionOffset = 0;
_positionChunk++;
}
if (count != 0)
{
byte[] chunk = new byte[count];
Array.Copy(buffer, offset, chunk, 0, count);
_chunks.Add(chunk);
_positionChunk = _chunks.Count;
_position += count;
}
}
}
class Program
{
static void Main(string[] args)
{
ChunkedMemoryStream cms = new ChunkedMemoryStream();
Debug.Assert(cms.Length == 0);
Debug.Assert(cms.Position == 0);
cms.Position = 0;
byte[] helloworld = Encoding.UTF8.GetBytes("hello world");
cms.Write(helloworld, 0, 3);
cms.Write(helloworld, 3, 3);
cms.Write(helloworld, 6, 5);
Debug.Assert(cms.Length == 11);
Debug.Assert(cms.Position == 11);
cms.Position = 0;
byte[] b = new byte[20];
cms.Read(b, 3, (int)cms.Length);
Debug.Assert(b.Skip(3).Take(11).SequenceEqual(helloworld));
cms.Position = 0;
cms.Write(Encoding.UTF8.GetBytes("seeya"), 0, 5);
Debug.Assert(cms.Length == 11);
Debug.Assert(cms.Position == 5);
cms.Position = 0;
cms.Read(b, 0, (byte) cms.Length);
Debug.Assert(b.Take(11).SequenceEqual(Encoding.UTF8.GetBytes("seeya world")));
Debug.Assert(cms.Length == 11);
Debug.Assert(cms.Position == 11);
cms.Write(Encoding.UTF8.GetBytes(" again"), 0, 6);
Debug.Assert(cms.Length == 17);
Debug.Assert(cms.Position == 17);
cms.Position = 0;
cms.Read(b, 0, (byte)cms.Length);
Debug.Assert(b.Take(17).SequenceEqual(Encoding.UTF8.GetBytes("seeya world again")));
}
}
Ответ 3
Команда Bing выпустила RecyclableMemoryStream и написала об этом здесь. Преимущества, которые они цитируют:
- Исключить выделение больших кусков объектов с помощью пустых буферов
- Начать гораздо меньше генераторов 2 GC и тратить гораздо меньше времени на паузу из-за GC
- Избегайте утечек памяти, имея размер ограниченного пула
- Избегать фрагментации памяти.
- Обеспечить отличную отлаживаемость
- Предоставить показатели для отслеживания производительности
Ответ 4
Я нашел аналогичную проблему в своем приложении. Я прочитал большое количество сжатых данных, и я страдал от OutOfMemoryException, используя MemoryStream. Я написал собственную реализацию потока "chunked" памяти на основе набора байтовых массивов. Если у вас есть идея, как сделать этот поток памяти более эффективным, напишите мне об этом.
public sealed class ChunkedMemoryStream : Stream
{
#region Constants
private const int BUFFER_LENGTH = 65536;
private const byte ONE = 1;
private const byte ZERO = 0;
#endregion
#region Readonly & Static Fields
private readonly Collection<byte[]> _chunks;
#endregion
#region Fields
private long _length;
private long _position;
private const byte TWO = 2;
#endregion
#region C'tors
public ChunkedMemoryStream()
{
_chunks = new Collection<byte[]> { new byte[BUFFER_LENGTH], new byte[BUFFER_LENGTH] };
_position = ZERO;
_length = ZERO;
}
#endregion
#region Instance Properties
public override bool CanRead
{
get { return true; }
}
public override bool CanSeek
{
get { return true; }
}
public override bool CanWrite
{
get { return true; }
}
public override long Length
{
get { return _length; }
}
public override long Position
{
get { return _position; }
set
{
if (!CanSeek)
throw new NotSupportedException();
_position = value;
if (_position > _length)
_position = _length - ONE;
}
}
private byte[] CurrentChunk
{
get
{
long positionDividedByBufferLength = _position / BUFFER_LENGTH;
var chunkIndex = Convert.ToInt32(positionDividedByBufferLength);
byte[] chunk = _chunks[chunkIndex];
return chunk;
}
}
private int PositionInChunk
{
get
{
int positionInChunk = Convert.ToInt32(_position % BUFFER_LENGTH);
return positionInChunk;
}
}
private int RemainingBytesInCurrentChunk
{
get
{
Contract.Ensures(Contract.Result<int>() > ZERO);
int remainingBytesInCurrentChunk = CurrentChunk.Length - PositionInChunk;
return remainingBytesInCurrentChunk;
}
}
#endregion
#region Instance Methods
public override void Flush()
{
}
public override int Read(byte[] buffer, int offset, int count)
{
if (offset + count > buffer.Length)
throw new ArgumentException();
if (buffer == null)
throw new ArgumentNullException();
if (offset < ZERO || count < ZERO)
throw new ArgumentOutOfRangeException();
if (!CanRead)
throw new NotSupportedException();
int bytesToRead = count;
if (_length - _position < bytesToRead)
bytesToRead = Convert.ToInt32(_length - _position);
int bytesreaded = 0;
while (bytesToRead > ZERO)
{
// get remaining bytes in current chunk
// read bytes in current chunk
// advance to next position
int remainingBytesInCurrentChunk = RemainingBytesInCurrentChunk;
if (remainingBytesInCurrentChunk > bytesToRead)
remainingBytesInCurrentChunk = bytesToRead;
Array.Copy(CurrentChunk, PositionInChunk, buffer, offset, remainingBytesInCurrentChunk);
//move position in source
_position += remainingBytesInCurrentChunk;
//move position in target
offset += remainingBytesInCurrentChunk;
//bytesToRead is smaller
bytesToRead -= remainingBytesInCurrentChunk;
//count readed bytes;
bytesreaded += remainingBytesInCurrentChunk;
}
return bytesreaded;
}
public override long Seek(long offset, SeekOrigin origin)
{
switch (origin)
{
case SeekOrigin.Begin:
Position = offset;
break;
case SeekOrigin.Current:
Position += offset;
break;
case SeekOrigin.End:
Position = Length + offset;
break;
}
return Position;
}
private long Capacity
{
get
{
int numberOfChunks = _chunks.Count;
long capacity = numberOfChunks * BUFFER_LENGTH;
return capacity;
}
}
public override void SetLength(long value)
{
if (value > _length)
{
while (value > Capacity)
{
var item = new byte[BUFFER_LENGTH];
_chunks.Add(item);
}
}
else if (value < _length)
{
var decimalValue = Convert.ToDecimal(value);
var valueToBeCompared = decimalValue % BUFFER_LENGTH == ZERO ? Capacity : Capacity - BUFFER_LENGTH;
//remove data chunks, but leave at least two chunks
while (value < valueToBeCompared && _chunks.Count > TWO)
{
byte[] lastChunk = _chunks.Last();
_chunks.Remove(lastChunk);
}
}
_length = value;
if (_position > _length - ONE)
_position = _length == 0 ? ZERO : _length - ONE;
}
public override void Write(byte[] buffer, int offset, int count)
{
if (!CanWrite)
throw new NotSupportedException();
int bytesToWrite = count;
while (bytesToWrite > ZERO)
{
//get remaining space in current chunk
int remainingBytesInCurrentChunk = RemainingBytesInCurrentChunk;
//if count of bytes to be written is fewer than remaining
if (remainingBytesInCurrentChunk > bytesToWrite)
remainingBytesInCurrentChunk = bytesToWrite;
//if remaining bytes is still greater than zero
if (remainingBytesInCurrentChunk > ZERO)
{
//write remaining bytes to current Chunk
Array.Copy(buffer, offset, CurrentChunk, PositionInChunk, remainingBytesInCurrentChunk);
//change offset of source array
offset += remainingBytesInCurrentChunk;
//change bytes to write
bytesToWrite -= remainingBytesInCurrentChunk;
//change length and position
_length += remainingBytesInCurrentChunk;
_position += remainingBytesInCurrentChunk;
}
if (Capacity == _position)
_chunks.Add(new byte[BUFFER_LENGTH]);
}
}
/// <summary>
/// Gets entire content of stream regardless of Position value and return output as byte array
/// </summary>
/// <returns>byte array</returns>
public byte[] ToArray()
{
var outputArray = new byte[Length];
if (outputArray.Length != ZERO)
{
long outputPosition = ZERO;
foreach (byte[] chunk in _chunks)
{
var remainingLength = (Length - outputPosition) > chunk.Length
? chunk.Length
: Length - outputPosition;
Array.Copy(chunk, ZERO, outputArray, outputPosition, remainingLength);
outputPosition = outputPosition + remainingLength;
}
}
return outputArray;
}
/// <summary>
/// Method set Position to first element and write entire stream to another
/// </summary>
/// <param name="stream">Target stream</param>
public void WriteTo(Stream stream)
{
Contract.Requires(stream != null);
Position = ZERO;
var buffer = new byte[BUFFER_LENGTH];
int bytesReaded;
do
{
bytesReaded = Read(buffer, ZERO, BUFFER_LENGTH);
stream.Write(buffer, ZERO, bytesReaded);
} while (bytesReaded > ZERO);
}
#endregion
}
Ответ 5
Вот полная реализация:
/// <summary>
/// Defines a MemoryStream that does not sit on the Large Object Heap, thus avoiding memory fragmentation.
/// </summary>
public sealed class ChunkedMemoryStream : Stream
{
/// <summary>
/// Defines the default chunk size. Currently defined as 0x10000.
/// </summary>
public const int DefaultChunkSize = 0x10000; // needs to be < 85000
private List<byte[]> _chunks = new List<byte[]>();
private long _position;
private int _chunkSize;
private int _lastChunkPos;
private int _lastChunkPosIndex;
/// <summary>
/// Initializes a new instance of the <see cref="ChunkedMemoryStream"/> class.
/// </summary>
public ChunkedMemoryStream()
: this(DefaultChunkSize)
{
}
/// <summary>
/// Initializes a new instance of the <see cref="ChunkedMemoryStream"/> class.
/// </summary>
/// <param name="chunkSize">Size of the underlying chunks.</param>
public ChunkedMemoryStream(int chunkSize)
: this(null)
{
}
/// <summary>
/// Initializes a new instance of the <see cref="ChunkedMemoryStream"/> class based on the specified byte array.
/// </summary>
/// <param name="buffer">The array of unsigned bytes from which to create the current stream.</param>
public ChunkedMemoryStream(byte[] buffer)
: this(DefaultChunkSize, buffer)
{
}
/// <summary>
/// Initializes a new instance of the <see cref="ChunkedMemoryStream"/> class based on the specified byte array.
/// </summary>
/// <param name="chunkSize">Size of the underlying chunks.</param>
/// <param name="buffer">The array of unsigned bytes from which to create the current stream.</param>
public ChunkedMemoryStream(int chunkSize, byte[] buffer)
{
FreeOnDispose = true;
ChunkSize = chunkSize;
_chunks.Add(new byte[chunkSize]);
if (buffer != null)
{
Write(buffer, 0, buffer.Length);
Position = 0;
}
}
/// <summary>
/// Gets or sets a value indicating whether to free the underlying chunks on dispose.
/// </summary>
/// <value><c>true</c> if [free on dispose]; otherwise, <c>false</c>.</value>
public bool FreeOnDispose { get; set; }
/// <summary>
/// Releases the unmanaged resources used by the <see cref="T:System.IO.Stream"/> and optionally releases the managed resources.
/// </summary>
/// <param name="disposing">true to release both managed and unmanaged resources; false to release only unmanaged resources.</param>
protected override void Dispose(bool disposing)
{
if (FreeOnDispose)
{
if (_chunks != null)
{
_chunks = null;
_chunkSize = 0;
_position = 0;
}
}
base.Dispose(disposing);
}
/// <summary>
/// When overridden in a derived class, clears all buffers for this stream and causes any buffered data to be written to the underlying device.
/// This implementation does nothing.
/// </summary>
public override void Flush()
{
// do nothing
}
/// <summary>
/// When overridden in a derived class, reads a sequence of bytes from the current stream and advances the position within the stream by the number of bytes read.
/// </summary>
/// <param name="buffer">An array of bytes. When this method returns, the buffer contains the specified byte array with the values between <paramref name="offset"/> and (<paramref name="offset"/> + <paramref name="count"/> - 1) replaced by the bytes read from the current source.</param>
/// <param name="offset">The zero-based byte offset in <paramref name="buffer"/> at which to begin storing the data read from the current stream.</param>
/// <param name="count">The maximum number of bytes to be read from the current stream.</param>
/// <returns>
/// The total number of bytes read into the buffer. This can be less than the number of bytes requested if that many bytes are not currently available, or zero (0) if the end of the stream has been reached.
/// </returns>
/// <exception cref="T:System.ArgumentException">
/// The sum of <paramref name="offset"/> and <paramref name="count"/> is larger than the buffer length.
/// </exception>
/// <exception cref="T:System.ArgumentNullException">
/// <paramref name="buffer"/> is null.
/// </exception>
/// <exception cref="T:System.ArgumentOutOfRangeException">
/// <paramref name="offset"/> or <paramref name="count"/> is negative.
/// </exception>
/// <exception cref="T:System.ObjectDisposedException">
/// Methods were called after the stream was closed.
/// </exception>
public override int Read(byte[] buffer, int offset, int count)
{
if (buffer == null)
throw new ArgumentNullException("buffer");
if (offset < 0)
throw new ArgumentOutOfRangeException("offset");
if (count < 0)
throw new ArgumentOutOfRangeException("count");
if ((buffer.Length - offset) < count)
throw new ArgumentException(null, "count");
CheckDisposed();
int chunkIndex = (int)(_position / ChunkSize);
if (chunkIndex == _chunks.Count)
return 0;
int chunkPos = (int)(_position % ChunkSize);
count = (int)Math.Min(count, Length - _position);
if (count == 0)
return 0;
int left = count;
int inOffset = offset;
int total = 0;
do
{
int toCopy = Math.Min(left, ChunkSize - chunkPos);
Buffer.BlockCopy(_chunks[chunkIndex], chunkPos, buffer, inOffset, toCopy);
inOffset += toCopy;
left -= toCopy;
total += toCopy;
if ((chunkPos + toCopy) == ChunkSize)
{
if (chunkIndex == (_chunks.Count - 1))
{
// last chunk
break;
}
chunkPos = 0;
chunkIndex++;
}
else
{
chunkPos += toCopy;
}
}
while (left > 0);
_position += total;
return total;
}
/// <summary>
/// Reads a byte from the stream and advances the position within the stream by one byte, or returns -1 if at the end of the stream.
/// </summary>
/// <returns>
/// The unsigned byte cast to an Int32, or -1 if at the end of the stream.
/// </returns>
/// <exception cref="T:System.ObjectDisposedException">
/// Methods were called after the stream was closed.
/// </exception>
public override int ReadByte()
{
CheckDisposed();
if (_position >= Length)
return -1;
byte b = _chunks[(int)(_position / ChunkSize)][_position % ChunkSize];
_position++;
return b;
}
/// <summary>
/// When overridden in a derived class, sets the position within the current stream.
/// </summary>
/// <param name="offset">A byte offset relative to the <paramref name="origin"/> parameter.</param>
/// <param name="origin">A value of type <see cref="T:System.IO.SeekOrigin"/> indicating the reference point used to obtain the new position.</param>
/// <returns>
/// The new position within the current stream.
/// </returns>
/// <exception cref="T:System.ObjectDisposedException">
/// Methods were called after the stream was closed.
/// </exception>
public override long Seek(long offset, SeekOrigin origin)
{
CheckDisposed();
switch (origin)
{
case SeekOrigin.Begin:
Position = offset;
break;
case SeekOrigin.Current:
Position += offset;
break;
case SeekOrigin.End:
Position = Length + offset;
break;
}
return Position;
}
private void CheckDisposed()
{
if (_chunks == null)
throw new ObjectDisposedException(null, "Cannot access a disposed stream");
}
/// <summary>
/// When overridden in a derived class, sets the length of the current stream.
/// </summary>
/// <param name="value">The desired length of the current stream in bytes.</param>
/// <exception cref="T:System.ObjectDisposedException">
/// Methods were called after the stream was closed.
/// </exception>
public override void SetLength(long value)
{
CheckDisposed();
if (value < 0)
throw new ArgumentOutOfRangeException("value");
if (value > Length)
throw new ArgumentOutOfRangeException("value");
long needed = value / ChunkSize;
if ((value % ChunkSize) != 0)
{
needed++;
}
if (needed > int.MaxValue)
throw new ArgumentOutOfRangeException("value");
if (needed < _chunks.Count)
{
int remove = (int)(_chunks.Count - needed);
for (int i = 0; i < remove; i++)
{
_chunks.RemoveAt(_chunks.Count - 1);
}
}
_lastChunkPos = (int)(value % ChunkSize);
}
/// <summary>
/// Converts the current stream to a byte array.
/// </summary>
/// <returns>An array of bytes</returns>
public byte[] ToArray()
{
CheckDisposed();
byte[] bytes = new byte[Length];
int offset = 0;
for (int i = 0; i < _chunks.Count; i++)
{
int count = (i == (_chunks.Count - 1)) ? _lastChunkPos : _chunks[i].Length;
if (count > 0)
{
Buffer.BlockCopy(_chunks[i], 0, bytes, offset, count);
offset += count;
}
}
return bytes;
}
/// <summary>
/// When overridden in a derived class, writes a sequence of bytes to the current stream and advances the current position within this stream by the number of bytes written.
/// </summary>
/// <param name="buffer">An array of bytes. This method copies <paramref name="count"/> bytes from <paramref name="buffer"/> to the current stream.</param>
/// <param name="offset">The zero-based byte offset in <paramref name="buffer"/> at which to begin copying bytes to the current stream.</param>
/// <param name="count">The number of bytes to be written to the current stream.</param>
/// <exception cref="T:System.ArgumentException">
/// The sum of <paramref name="offset"/> and <paramref name="count"/> is greater than the buffer length.
/// </exception>
/// <exception cref="T:System.ArgumentNullException">
/// <paramref name="buffer"/> is null.
/// </exception>
/// <exception cref="T:System.ArgumentOutOfRangeException">
/// <paramref name="offset"/> or <paramref name="count"/> is negative.
/// </exception>
/// <exception cref="T:System.ObjectDisposedException">
/// Methods were called after the stream was closed.
/// </exception>
public override void Write(byte[] buffer, int offset, int count)
{
if (buffer == null)
throw new ArgumentNullException("buffer");
if (offset < 0)
throw new ArgumentOutOfRangeException("offset");
if (count < 0)
throw new ArgumentOutOfRangeException("count");
if ((buffer.Length - offset) < count)
throw new ArgumentException(null, "count");
CheckDisposed();
int chunkPos = (int)(_position % ChunkSize);
int chunkIndex = (int)(_position / ChunkSize);
if (chunkIndex == _chunks.Count)
{
_chunks.Add(new byte[ChunkSize]);
}
int left = count;
int inOffset = offset;
do
{
int copied = Math.Min(left, ChunkSize - chunkPos);
Buffer.BlockCopy(buffer, inOffset, _chunks[chunkIndex], chunkPos, copied);
inOffset += copied;
left -= copied;
if ((chunkPos + copied) == ChunkSize)
{
chunkIndex++;
chunkPos = 0;
if (chunkIndex == _chunks.Count)
{
_chunks.Add(new byte[ChunkSize]);
}
}
else
{
chunkPos += copied;
}
}
while (left > 0);
_position += count;
if (chunkIndex == (_chunks.Count - 1))
{
if ((chunkIndex > _lastChunkPosIndex) ||
((chunkIndex == _lastChunkPosIndex) && (chunkPos > _lastChunkPos)))
{
_lastChunkPos = chunkPos;
_lastChunkPosIndex = chunkIndex;
}
}
}
/// <summary>
/// Writes a byte to the current position in the stream and advances the position within the stream by one byte.
/// </summary>
/// <param name="value">The byte to write to the stream.</param>
/// <exception cref="T:System.ObjectDisposedException">
/// Methods were called after the stream was closed.
/// </exception>
public override void WriteByte(byte value)
{
CheckDisposed();
int chunkIndex = (int)(_position / ChunkSize);
int chunkPos = (int)(_position % ChunkSize);
if (chunkPos > (ChunkSize - 1)) //changed from (chunkPos >= (ChunkSize - 1))
{
chunkIndex++;
chunkPos = 0;
if (chunkIndex == _chunks.Count)
{
_chunks.Add(new byte[ChunkSize]);
}
}
_chunks[chunkIndex][chunkPos++] = value;
_position++;
if (chunkIndex == (_chunks.Count - 1))
{
if ((chunkIndex > _lastChunkPosIndex) ||
((chunkIndex == _lastChunkPosIndex) && (chunkPos > _lastChunkPos)))
{
_lastChunkPos = chunkPos;
_lastChunkPosIndex = chunkIndex;
}
}
}
/// <summary>
/// Writes to the specified stream.
/// </summary>
/// <param name="stream">The stream.</param>
public void WriteTo(Stream stream)
{
if (stream == null)
throw new ArgumentNullException("stream");
CheckDisposed();
for (int i = 0; i < _chunks.Count; i++)
{
int count = (i == (_chunks.Count - 1)) ? _lastChunkPos : _chunks[i].Length;
stream.Write(_chunks[i], 0, count);
}
}
/// <summary>
/// When overridden in a derived class, gets a value indicating whether the current stream supports reading.
/// </summary>
/// <value></value>
/// <returns>true if the stream supports reading; otherwise, false.
/// </returns>
public override bool CanRead
{
get
{
return true;
}
}
/// <summary>
/// When overridden in a derived class, gets a value indicating whether the current stream supports seeking.
/// </summary>
/// <value></value>
/// <returns>true if the stream supports seeking; otherwise, false.
/// </returns>
public override bool CanSeek
{
get
{
return true;
}
}
/// <summary>
/// When overridden in a derived class, gets a value indicating whether the current stream supports writing.
/// </summary>
/// <value></value>
/// <returns>true if the stream supports writing; otherwise, false.
/// </returns>
public override bool CanWrite
{
get
{
return true;
}
}
/// <summary>
/// When overridden in a derived class, gets the length in bytes of the stream.
/// </summary>
/// <value></value>
/// <returns>
/// A long value representing the length of the stream in bytes.
/// </returns>
/// <exception cref="T:System.ObjectDisposedException">
/// Methods were called after the stream was closed.
/// </exception>
public override long Length
{
get
{
CheckDisposed();
if (_chunks.Count == 0)
return 0;
return (_chunks.Count - 1) * ChunkSize + _lastChunkPos;
}
}
/// <summary>
/// Gets or sets the size of the underlying chunks. Cannot be greater than or equal to 85000.
/// </summary>
/// <value>The chunks size.</value>
public int ChunkSize
{
get
{
return _chunkSize;
}
set
{
if ((value <= 0) || (value >= 85000))
throw new ArgumentOutOfRangeException("value");
_chunkSize = value;
}
}
/// <summary>
/// When overridden in a derived class, gets or sets the position within the current stream.
/// </summary>
/// <value></value>
/// <returns>
/// The current position within the stream.
/// </returns>
/// <exception cref="T:System.ObjectDisposedException">
/// Methods were called after the stream was closed.
/// </exception>
public override long Position
{
get
{
CheckDisposed();
return _position;
}
set
{
CheckDisposed();
if (value < 0)
throw new ArgumentOutOfRangeException("value");
if (value > Length)
throw new ArgumentOutOfRangeException("value");
_position = value;
}
}
}
Ответ 6
вы можете использовать этот
http://www.123aspx.com/Rotor/src/chunkedmemorystream.cs.txt
Ответ 7
Вы должны использовать UnmanagedMemoryStream при работе с блоками памяти объемом более 2 ГБ, поскольку MemoryStream ограничивается 2 ГБ, а UnmanagedMemoryStream был создан для решения этой проблемы.
Ответ 8
SparseMemoryStream делает это в .NET в глубоком углублении во внутренней библиотеке классов - конечно, исходный код доступен, так как Microsoft все это выложила в виде открытого источника.
Вы можете взять здесь код: http://www.dotnetframework.org/default.aspx/[email protected]/[email protected]/DEVDIV_TFS/Dev10/Releases/RTMRel/wpf/src/Base/MS/Internal/IO/Packaging/[email protected]/1305600/[email protected]
Как я уже сказал, я настоятельно рекомендую не использовать его как есть - по крайней мере, удалить все вызовы IsolStorage для стартеров, поскольку это, по-видимому, является причиной отсутствия ошибок * в API упаковки.
(*: В дополнение к распространению данных в потоках, если он становится слишком большим, он по существу восстанавливает файлы подкачки по какой-либо причине - в изолированном хранилище пользователей не менее - и по совпадению большинство продуктов MS, которые позволяют У .NET-надстроек нет настроек доменов приложений таким образом, что вы можете получить доступ к изолированному хранилищу. Например, надстройки VSTO печально известны этой проблемой.)
Ответ 9
Другая реализация потокового потока может рассматриваться как замена памяти MemoryStream. Кроме того, он позволяет выделять один большой массив байтов на LOH, который будет использоваться как пул "chunk", разделяемый всеми экземплярами ChunkedStream...
https://github.com/ImmortalGAD/ChunkedStream
