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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// Copied from https://github.com/dotnet/corefx/blob/b0751dcd4a419ba6731dcaa7d240a8a1946c934c/src/System.Text.Json/src/System/Text/Json/Serialization/ArrayBufferWriter.cs
using System.Diagnostics;
namespace System.Buffers;
internal sealed class PooledArrayBufferWriter<T> : IBufferWriter<T>, IDisposable
{
private T[] _rentedBuffer;
private int _index;
private const int MinimumBufferSize = 256;
public PooledArrayBufferWriter()
{
_rentedBuffer = ArrayPool<T>.Shared.Rent(MinimumBufferSize);
_index = 0;
}
public PooledArrayBufferWriter(int initialCapacity)
{
ArgumentOutOfRangeException.ThrowIfNegativeOrZero(initialCapacity);
_rentedBuffer = ArrayPool<T>.Shared.Rent(initialCapacity);
_index = 0;
}
public ReadOnlyMemory<T> WrittenMemory
{
get
{
CheckIfDisposed();
return _rentedBuffer.AsMemory(0, _index);
}
}
public int WrittenCount
{
get
{
CheckIfDisposed();
return _index;
}
}
public int Capacity
{
get
{
CheckIfDisposed();
return _rentedBuffer.Length;
}
}
public int FreeCapacity
{
get
{
CheckIfDisposed();
return _rentedBuffer.Length - _index;
}
}
public void Clear()
{
CheckIfDisposed();
ClearHelper();
}
private void ClearHelper()
{
Debug.Assert(_rentedBuffer != null);
_rentedBuffer.AsSpan(0, _index).Clear();
_index = 0;
}
// Returns the rented buffer back to the pool
public void Dispose()
{
if (_rentedBuffer == null)
{
return;
}
ClearHelper();
ArrayPool<T>.Shared.Return(_rentedBuffer);
_rentedBuffer = null;
}
private void CheckIfDisposed()
{
if (_rentedBuffer == null)
{
ThrowObjectDisposedException();
}
}
private static void ThrowObjectDisposedException()
{
throw new ObjectDisposedException(nameof(ArrayBufferWriter<T>));
}
public void Advance(int count)
{
CheckIfDisposed();
ArgumentOutOfRangeException.ThrowIfNegative(count);
if (_index > _rentedBuffer.Length - count)
{
ThrowInvalidOperationException(_rentedBuffer.Length);
}
_index += count;
}
public Memory<T> GetMemory(int sizeHint = 0)
{
CheckIfDisposed();
CheckAndResizeBuffer(sizeHint);
return _rentedBuffer.AsMemory(_index);
}
public Span<T> GetSpan(int sizeHint = 0)
{
CheckIfDisposed();
CheckAndResizeBuffer(sizeHint);
return _rentedBuffer.AsSpan(_index);
}
private void CheckAndResizeBuffer(int sizeHint)
{
Debug.Assert(_rentedBuffer != null);
ArgumentOutOfRangeException.ThrowIfNegative(sizeHint);
if (sizeHint == 0)
{
sizeHint = MinimumBufferSize;
}
var availableSpace = _rentedBuffer.Length - _index;
if (sizeHint > availableSpace)
{
var growBy = Math.Max(sizeHint, _rentedBuffer.Length);
var newSize = checked(_rentedBuffer.Length + growBy);
var oldBuffer = _rentedBuffer;
_rentedBuffer = ArrayPool<T>.Shared.Rent(newSize);
Debug.Assert(oldBuffer.Length >= _index);
Debug.Assert(_rentedBuffer.Length >= _index);
var previousBuffer = oldBuffer.AsSpan(0, _index);
previousBuffer.CopyTo(_rentedBuffer);
previousBuffer.Clear();
ArrayPool<T>.Shared.Return(oldBuffer);
}
Debug.Assert(_rentedBuffer.Length - _index > 0);
Debug.Assert(_rentedBuffer.Length - _index >= sizeHint);
}
private static void ThrowInvalidOperationException(int capacity)
{
throw new InvalidOperationException($"Cannot advance past the end of the buffer, which has a size of {capacity}.");
}
}
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