Code:
/ FXUpdate3074 / FXUpdate3074 / 1.1 / untmp / whidbey / QFE / ndp / clr / src / BCL / System / IO / BufferedStream.cs / 2 / BufferedStream.cs
// ==++==
//
// Copyright (c) Microsoft Corporation. All rights reserved.
//
// ==--==
/*============================================================
**
** Class: BufferedStream
**
** Purpose: A composable Stream that buffers reads & writes
** to the underlying stream.
**
**
===========================================================*/
using System;
using System.Runtime.InteropServices;
using System.Globalization;
namespace System.IO {
// This is a somewhat complex but efficient implementation. The biggest
// design goal here is to prevent the buffer from getting in the way and slowing
// down IO accesses when it isn't needed. If you always read & write for sizes
// greater than the internal buffer size, then this class may not even allocate
// the internal buffer. Secondly, it buffers reads & writes in a shared buffer.
// (If you maintained two buffers separately, one operation would always trash
// the other buffer anyways, so we might as well use one buffer.) The
// assumption here is you will almost always be doing a series of reads or
// writes, but rarely alternate between the two of them on the same stream.
//
// This is adaptive buffering code. I had some ideas to make the pathological case better
// here, but the pathological cases for the new code would have avoided
// memcpy's by introducing more disk writes (which are 3 orders of magnitude
// slower). I've made some optimizations, fixed several bugs, and
// tried documenting this code. --
//
// Possible
[ComVisible(true)]
public sealed class BufferedStream : Stream {
private Stream _s; // Underlying stream. Close sets _s to null.
private byte[] _buffer; // Shared read/write buffer. Alloc on first use.
private int _readPos; // Read pointer within shared buffer.
private int _readLen; // Number of bytes read in buffer from _s.
private int _writePos; // Write pointer within shared buffer.
private int _bufferSize; // Length of internal buffer, if it's allocated.
private const int _DefaultBufferSize = 4096;
private BufferedStream() {}
public BufferedStream(Stream stream) : this(stream, _DefaultBufferSize)
{
}
public BufferedStream(Stream stream, int bufferSize)
{
if (stream==null)
throw new ArgumentNullException("stream");
if (bufferSize <= 0)
throw new ArgumentOutOfRangeException("bufferSize", String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("ArgumentOutOfRange_MustBePositive"), "bufferSize"));
BCLDebug.Perf(!(stream is FileStream), "FileStream is buffered - don't wrap it in a BufferedStream");
BCLDebug.Perf(!(stream is MemoryStream), "MemoryStream shouldn't be wrapped in a BufferedStream!");
_s = stream;
_bufferSize = bufferSize;
// Allocate _buffer on its first use - it will not be used if all reads
// & writes are greater than or equal to buffer size.
if (!_s.CanRead && !_s.CanWrite) __Error.StreamIsClosed();
}
public override bool CanRead {
get { return _s != null && _s.CanRead; }
}
public override bool CanWrite {
get { return _s != null && _s.CanWrite; }
}
public override bool CanSeek {
get { return _s != null && _s.CanSeek; }
}
public override long Length {
get {
if (_s==null) __Error.StreamIsClosed();
if (_writePos > 0) FlushWrite();
return _s.Length;
}
}
public override long Position {
get {
if (_s==null) __Error.StreamIsClosed();
if (!_s.CanSeek) __Error.SeekNotSupported();
// return _s.Seek(0, SeekOrigin.Current) + (_readPos + _writePos - _readLen);
return _s.Position + (_readPos - _readLen + _writePos);
}
set {
if (value < 0) throw new ArgumentOutOfRangeException("value", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
if (_s==null) __Error.StreamIsClosed();
if (!_s.CanSeek) __Error.SeekNotSupported();
if (_writePos > 0) FlushWrite();
_readPos = 0;
_readLen = 0;
_s.Seek(value, SeekOrigin.Begin);
}
}
protected override void Dispose(bool disposing)
{
try {
if (disposing && _s != null) {
try {
Flush();
}
finally {
_s.Close();
}
}
}
finally {
_s = null;
_buffer = null;
// Call base.Dispose(bool) to cleanup async IO resources
base.Dispose(disposing);
}
}
public override void Flush() {
if (_s==null) __Error.StreamIsClosed();
if (_writePos > 0) {
FlushWrite();
}
else if (_readPos < _readLen && _s.CanSeek) {
FlushRead();
}
_readPos = 0;
_readLen = 0;
}
// Reading is done by blocks from the file, but someone could read
// 1 byte from the buffer then write. At that point, the OS's file
// pointer is out of sync with the stream's position. All write
// functions should call this function to preserve the position in the file.
private void FlushRead() {
BCLDebug.Assert(_writePos == 0, "BufferedStream: Write buffer must be empty in FlushRead!");
if (_readPos - _readLen != 0)
_s.Seek(_readPos - _readLen, SeekOrigin.Current);
_readPos = 0;
_readLen = 0;
}
// Writes are buffered. Anytime the buffer fills up
// (_writePos + delta > _bufferSize) or the buffer switches to reading
// and there is dirty data (_writePos > 0), this function must be called.
private void FlushWrite() {
BCLDebug.Assert(_readPos == 0 && _readLen == 0, "BufferedStream: Read buffer must be empty in FlushWrite!");
_s.Write(_buffer, 0, _writePos);
_writePos = 0;
_s.Flush();
}
public override int Read([In, Out] byte[] array, int offset, int count) {
if (array==null)
throw new ArgumentNullException("array", Environment.GetResourceString("ArgumentNull_Buffer"));
if (offset < 0)
throw new ArgumentOutOfRangeException("offset", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
if (count < 0)
throw new ArgumentOutOfRangeException("count", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
if (array.Length - offset < count)
throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
if (_s==null) __Error.StreamIsClosed();
int n = _readLen - _readPos;
// if the read buffer is empty, read into either user's array or our
// buffer, depending on number of bytes user asked for and buffer size.
if (n == 0) {
if (!_s.CanRead) __Error.ReadNotSupported();
if (_writePos > 0) FlushWrite();
if (count >= _bufferSize) {
n = _s.Read(array, offset, count);
// Throw away read buffer.
_readPos = 0;
_readLen = 0;
return n;
}
if (_buffer == null) _buffer = new byte[_bufferSize];
n = _s.Read(_buffer, 0, _bufferSize);
if (n == 0) return 0;
_readPos = 0;
_readLen = n;
}
// Now copy min of count or numBytesAvailable (ie, near EOF) to array.
if (n > count) n = count;
Buffer.InternalBlockCopy(_buffer, _readPos, array, offset, n);
_readPos += n;
// We may have read less than the number of bytes the user asked
// for, but that is part of the Stream contract. Reading again for
// more data may cause us to block if we're using a device with
// no clear end of file, such as a serial port or pipe. If we
// blocked here & this code was used with redirected pipes for a
// process's standard output, this can lead to deadlocks involving
// two processes.
// BUT - this is a breaking change.
// If we hit the end of the buffer and didn't have enough bytes, we must
// read some more from the underlying stream.
if (n < count) {
int moreBytesRead = _s.Read(array, offset + n, count - n);
n += moreBytesRead;
_readPos = 0;
_readLen = 0;
}
return n;
}
// Reads a byte from the underlying stream. Returns the byte cast to an int
// or -1 if reading from the end of the stream.
public override int ReadByte() {
if (_s==null) __Error.StreamIsClosed();
if (_readLen==0 && !_s.CanRead) __Error.ReadNotSupported();
if (_readPos == _readLen) {
if (_writePos > 0) FlushWrite();
if (_buffer == null) _buffer = new byte[_bufferSize];
_readLen = _s.Read(_buffer, 0, _bufferSize);
_readPos = 0;
}
if (_readPos == _readLen) return -1;
return _buffer[_readPos++];
}
public override void Write(byte[] array, int offset, int count) {
if (array==null)
throw new ArgumentNullException("array", Environment.GetResourceString("ArgumentNull_Buffer"));
if (offset < 0)
throw new ArgumentOutOfRangeException("offset", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
if (count < 0)
throw new ArgumentOutOfRangeException("count", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
if (array.Length - offset < count)
throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
if (_s==null) __Error.StreamIsClosed();
if (_writePos==0) {
// Ensure we can write to the stream, and ready buffer for writing.
if (!_s.CanWrite) __Error.WriteNotSupported();
if (_readPos < _readLen)
FlushRead();
else {
_readPos = 0;
_readLen = 0;
}
}
// If our buffer has data in it, copy data from the user's array into
// the buffer, and if we can fit it all there, return. Otherwise, write
// the buffer to disk and copy any remaining data into our buffer.
// The assumption here is memcpy is cheaper than disk (or net) IO.
// (10 milliseconds to disk vs. ~20-30 microseconds for a 4K memcpy)
// So the extra copying will reduce the total number of writes, in
// non-pathological cases (ie, write 1 byte, then write for the buffer
// size repeatedly)
if (_writePos > 0) {
int numBytes = _bufferSize - _writePos; // space left in buffer
if (numBytes > 0) {
if (numBytes > count)
numBytes = count;
Buffer.InternalBlockCopy(array, offset, _buffer, _writePos, numBytes);
_writePos += numBytes;
if (count==numBytes) return;
offset += numBytes;
count -= numBytes;
}
// Reset our buffer. We essentially want to call FlushWrite
// without calling Flush on the underlying Stream.
_s.Write(_buffer, 0, _writePos);
_writePos = 0;
}
// If the buffer would slow writes down, avoid buffer completely.
if (count >= _bufferSize) {
BCLDebug.Assert(_writePos == 0, "BufferedStream cannot have buffered data to write here! Your stream will be corrupted.");
_s.Write(array, offset, count);
return;
}
else if (count == 0)
return; // Don't allocate a buffer then call memcpy for 0 bytes.
if (_buffer==null) _buffer = new byte[_bufferSize];
// Copy remaining bytes into buffer, to write at a later date.
Buffer.InternalBlockCopy(array, offset, _buffer, 0, count);
_writePos = count;
}
public override void WriteByte(byte value) {
if (_s==null) __Error.StreamIsClosed();
if (_writePos==0) {
if (!_s.CanWrite) __Error.WriteNotSupported();
if (_readPos < _readLen)
FlushRead();
else {
_readPos = 0;
_readLen = 0;
}
if (_buffer==null) _buffer = new byte[_bufferSize];
}
if (_writePos == _bufferSize)
FlushWrite();
_buffer[_writePos++] = value;
}
public override long Seek(long offset, SeekOrigin origin)
{
if (_s==null) __Error.StreamIsClosed();
if (!_s.CanSeek) __Error.SeekNotSupported();
// If we've got bytes in our buffer to write, write them out.
// If we've read in and consumed some bytes, we'll have to adjust
// our seek positions ONLY IF we're seeking relative to the current
// position in the stream.
BCLDebug.Assert(_readPos <= _readLen, "_readPos <= _readLen");
if (_writePos > 0) {
FlushWrite();
}
else if (origin == SeekOrigin.Current) {
// Don't call FlushRead here, which would have caused an infinite
// loop. Simply adjust the seek origin. This isn't necessary
// if we're seeking relative to the beginning or end of the stream.
BCLDebug.Assert(_readLen - _readPos >= 0, "_readLen ("+_readLen+") - _readPos ("+_readPos+") >= 0");
offset -= (_readLen - _readPos);
}
/*
_readPos = 0;
_readLen = 0;
return _s.Seek(offset, origin);
*/
long oldPos = _s.Position + (_readPos - _readLen);
long pos = _s.Seek(offset, origin);
// We now must update the read buffer. We can in some cases simply
// update _readPos within the buffer, copy around the buffer so our
// Position property is still correct, and avoid having to do more
// reads from the disk. Otherwise, discard the buffer's contents.
if (_readLen > 0) {
// We can optimize the following condition:
// oldPos - _readPos <= pos < oldPos + _readLen - _readPos
if (oldPos == pos) {
if (_readPos > 0) {
//Console.WriteLine("Seek: seeked for 0, adjusting buffer back by: "+_readPos+" _readLen: "+_readLen);
Buffer.InternalBlockCopy(_buffer, _readPos, _buffer, 0, _readLen - _readPos);
_readLen -= _readPos;
_readPos = 0;
}
// If we still have buffered data, we must update the stream's
// position so our Position property is correct.
if (_readLen > 0)
_s.Seek(_readLen, SeekOrigin.Current);
}
else if (oldPos - _readPos < pos && pos < oldPos + _readLen - _readPos) {
int diff = (int)(pos - oldPos);
//Console.WriteLine("Seek: diff was "+diff+", readpos was "+_readPos+" adjusting buffer - shrinking by "+ (_readPos + diff));
Buffer.InternalBlockCopy(_buffer, _readPos+diff, _buffer, 0, _readLen - (_readPos + diff));
_readLen -= (_readPos + diff);
_readPos = 0;
if (_readLen > 0)
_s.Seek(_readLen, SeekOrigin.Current);
}
else {
// Lose the read buffer.
_readPos = 0;
_readLen = 0;
}
BCLDebug.Assert(_readLen >= 0 && _readPos <= _readLen, "_readLen should be nonnegative, and _readPos should be less than or equal _readLen");
BCLDebug.Assert(pos == Position, "Seek optimization: pos != Position! Buffer math was mangled.");
}
return pos;
}
public override void SetLength(long value) {
if (value < 0) throw new ArgumentOutOfRangeException("value", Environment.GetResourceString("ArgumentOutOfRange_NegFileSize"));
if (_s==null) __Error.StreamIsClosed();
if (!_s.CanSeek) __Error.SeekNotSupported();
if (!_s.CanWrite) __Error.WriteNotSupported();
if (_writePos > 0) {
FlushWrite();
}
else if (_readPos < _readLen) {
FlushRead();
}
_readPos = 0;
_readLen = 0;
_s.SetLength(value);
}
}
}
// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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