因为this is the algorithm 是如何扩展其容量的。
public override void Write(byte[] buffer, int offset, int count) {
//... Removed Error checking for example
int i = _position + count;
// Check for overflow
if (i < 0)
throw new IOException(Environment.GetResourceString("IO.IO_StreamTooLong"));
if (i > _length) {
bool mustZero = _position > _length;
if (i > _capacity) {
bool allocatedNewArray = EnsureCapacity(i);
if (allocatedNewArray)
mustZero = false;
}
if (mustZero)
Array.Clear(_buffer, _length, i - _length);
_length = i;
}
//...
}
private bool EnsureCapacity(int value) {
// Check for overflow
if (value < 0)
throw new IOException(Environment.GetResourceString("IO.IO_StreamTooLong"));
if (value > _capacity) {
int newCapacity = value;
if (newCapacity < 256)
newCapacity = 256;
if (newCapacity < _capacity * 2)
newCapacity = _capacity * 2;
Capacity = newCapacity;
return true;
}
return false;
}
public virtual int Capacity
{
//...
set {
//...
// MemoryStream has this invariant: _origin > 0 => !expandable (see ctors)
if (_expandable && value != _capacity) {
if (value > 0) {
byte[] newBuffer = new byte[value];
if (_length > 0) Buffer.InternalBlockCopy(_buffer, 0, newBuffer, 0, _length);
_buffer = newBuffer;
}
else {
_buffer = null;
}
_capacity = value;
}
}
}
因此，每次您达到容量限制时，容量都会增加一倍。这样做的原因是 Buffer.InternalBlockCopy 操作对于大型数组来说很慢，所以如果它必须频繁调整每个 Write 调用的大小，性能会显着下降。
您可以做几件事来提高性能您正在使用的内存。
const double ResizeFactor = 1.25;
private byte[] Decompress(byte[] data)
{
using (MemoryStream compressedStream = new MemoryStream(data))
using (GZipStream zipStream = new GZipStream(compressedStream, CompressionMode.Decompress))
using (MemoryStream resultStream = new MemoryStream(data.Length * ResizeFactor)) //Set the initial size to be the same as the compressed size + 25%.
{
byte[] buffer = new byte[4096];
int iCount = 0;
while ((iCount = zipStream.Read(buffer, 0, buffer.Length)) > 0)
{
if(resultStream.Capacity < resultStream.Length + iCount)
resultStream.Capacity = resultStream.Capacity * ResizeFactor; //Resize to 125% instead of 200%
resultStream.Write(buffer, 0, iCount);
}
return resultStream.ToArray();
}
}
如果你愿意，你可以做更多花哨的算法，比如根据当前压缩比调整大小
const double MinResizeFactor = 1.05;
private byte[] Decompress(byte[] data)
{
using (MemoryStream compressedStream = new MemoryStream(data))
using (GZipStream zipStream = new GZipStream(compressedStream, CompressionMode.Decompress))
using (MemoryStream resultStream = new MemoryStream(data.Length * MinResizeFactor)) //Set the initial size to be the same as the compressed size + the minimum resize factor.
{
byte[] buffer = new byte[4096];
int iCount = 0;
while ((iCount = zipStream.Read(buffer, 0, buffer.Length)) > 0)
{
if(resultStream.Capacity < resultStream.Length + iCount)
{
double sizeRatio = ((double)resultStream.Position + iCount) / (compressedStream.Position + 1); //The +1 is to prevent divide by 0 errors, it may not be necessary in practice.
//Resize to minimum resize factor of the current capacity or the
// compressed stream length times the compression ratio + min resize
// factor, whichever is larger.
resultStream.Capacity = Math.Max(resultStream.Capacity * MinResizeFactor,
(sizeRatio + (MinResizeFactor - 1)) * compressedStream.Length);
}
resultStream.Write(buffer, 0, iCount);
}
return resultStream.ToArray();
}
}