|
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System;
using System.Collections.Immutable;
using System.Diagnostics;
using System.IO;
using System.Reflection.Metadata;
using Microsoft.CodeAnalysis.PooledObjects;
using Microsoft.CodeAnalysis;
namespace Roslyn.Utilities
{
/// <summary>
/// A write-only memory stream backed by a <see cref="BlobBuilder"/>.
/// </summary>
internal sealed class BlobBuildingStream : Stream
{
private static readonly ObjectPool<BlobBuildingStream> s_pool = new ObjectPool<BlobBuildingStream>(() => new BlobBuildingStream());
private readonly BlobBuilder _builder;
/// <summary>
/// The chunk size to be used by the underlying BlobBuilder.
/// </summary>
/// <remarks>
/// The current single use case for this type is embedded sources in PDBs.
///
/// 32 KB is:
///
/// * Large enough to handle 99.6% all VB and C# files in Roslyn and CoreFX
/// without allocating additional chunks.
///
/// * Small enough to avoid the large object heap.
///
/// * Large enough to handle the files in the 0.4% case without allocating tons
/// of small chunks. Very large source files are often generated in build
/// (e.g. Syntax.xml.Generated.vb is 390KB compressed!) and those are actually
/// attractive candidates for embedding, so we don't want to discount the large
/// case too heavily.)
///
/// * We pool the outer BlobBuildingStream but only retain the first allocated chunk.
/// </remarks>
public const int ChunkSize = 32 * 1024;
public override bool CanWrite => true;
public override bool CanRead => false;
public override bool CanSeek => false;
public override long Length => _builder.Count;
public static BlobBuildingStream GetInstance()
{
return s_pool.Allocate();
}
private BlobBuildingStream()
{
// NOTE: We pool the wrapping BlobBuildingStream, but not individual chunks.
// The first chunk will be reused, but any further chunks will be freed when we're done building blob.
_builder = new BlobBuilder(ChunkSize);
}
public override void Write(byte[] buffer, int offset, int count)
{
_builder.WriteBytes(buffer, offset, count);
}
public override void WriteByte(byte value)
{
_builder.WriteByte(value);
}
public void WriteInt32(int value)
{
_builder.WriteInt32(value);
}
public Blob ReserveBytes(int byteCount)
{
return _builder.ReserveBytes(byteCount);
}
public ImmutableArray<byte> ToImmutableArray()
{
return _builder.ToImmutableArray();
}
public void Free()
{
_builder.Clear(); // frees all but first chunk
s_pool.Free(this); // return first chunk to pool
}
public override void Flush()
{
}
protected override void Dispose(bool disposing)
{
Debug.Assert(disposing);
Free();
}
public override long Seek(long offset, SeekOrigin origin)
{
throw new NotSupportedException();
}
public override int Read(byte[] buffer, int offset, int count)
{
throw new NotSupportedException();
}
public override void SetLength(long value)
{
throw new NotSupportedException();
}
public override long Position
{
get { throw new NotSupportedException(); }
set { throw new NotSupportedException(); }
}
}
}
|