Enable async-over-sync FileStream read/writes to be cancelable on Windows

[stephentoub]

Using the same helpers we previously used to enable this in pipe streams on Windows, enable FileStream.Read/WriteAsync on a FileStream created for synchronous I/O to be cancelable. This also makes some tweaks to those helpers to reduce allocation when a cancelable token is supplied.

Fixes #84290

This also makes some tweaks to those helpers to reduce allocation when a cancelable token is supplied. There's no meaningful improvement for FileStream, since it was effectively ignoring the CancellationToken previously. So here's a benchmark showing the impact on PipeStream, which as noted was already cancelable using this mechanism:

Method	Toolchain	Mean	Ratio	Allocated	Alloc Ratio
ReadWriteAsync	\main\corerun.exe	3.979 us	1.00	84 B	1.00
ReadWriteAsync	\pr\corerun.exe	3.342 us	0.85	2 B	0.02

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System.IO.Pipes;
using System.Threading.Tasks;
using System.Threading;

[MemoryDiagnoser(false)]
public class Program
{
    static void Main(string[] args) => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

    private readonly CancellationTokenSource _cts = new CancellationTokenSource();
    private readonly byte[] _buffer = new byte[1];
    private AnonymousPipeServerStream _server;
    private AnonymousPipeClientStream _client;

    [GlobalSetup]
    public void Setup()
    {
        _server = new AnonymousPipeServerStream(PipeDirection.Out);
        _client = new AnonymousPipeClientStream(PipeDirection.In, _server.ClientSafePipeHandle);
    }

    [GlobalCleanup]
    public void Cleanup()
    {
        _server.Dispose();
        _client.Dispose();
    }

    [Benchmark(OperationsPerInvoke = 1000)]
    public async Task ReadWriteAsync()
    {
        for (int i = 0; i < 1000; i++)
        {
            ValueTask<int> read = _client.ReadAsync(_buffer, _cts.Token);
            await _server.WriteAsync(_buffer, _cts.Token);
            await read;
        }
    }
}

[ghost]

Tagging subscribers to this area: @dotnet/area-system-io
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Using the same helpers we previously used to enable this in pipe streams on Windows, enable FileStream.Read/WriteAsync on a FileStream created for synchronous I/O to be cancelable. This also makes some tweaks to those helpers to reduce allocation when a cancelable token is supplied.

Fixes #84290

This also makes some tweaks to those helpers to reduce allocation when a cancelable token is supplied. There's no meaningful improvement for FileStream, since it was effectively ignoring the CancellationToken previously. So here's a benchmark showing the impact on PipeStream, which as noted was already cancelable using this mechanism:

Method	Toolchain	Mean	Ratio	Allocated	Alloc Ratio
ReadWriteAsync	\main\corerun.exe	3.979 us	1.00	84 B	1.00
ReadWriteAsync	\pr\corerun.exe	3.342 us	0.85	2 B	0.02

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System.IO.Pipes;
using System.Threading.Tasks;
using System.Threading;

[MemoryDiagnoser(false)]
public class Program
{
    static void Main(string[] args) => BenchmarkSwitcher.FromAssembly(typeof(Program).Assembly).Run(args);

    private readonly CancellationTokenSource _cts = new CancellationTokenSource();
    private readonly byte[] _buffer = new byte[1];
    private AnonymousPipeServerStream _server;
    private AnonymousPipeClientStream _client;

    [GlobalSetup]
    public void Setup()
    {
        _server = new AnonymousPipeServerStream(PipeDirection.Out);
        _client = new AnonymousPipeClientStream(PipeDirection.In, _server.ClientSafePipeHandle);
    }

    [GlobalCleanup]
    public void Cleanup()
    {
        _server.Dispose();
        _client.Dispose();
    }

    [Benchmark(OperationsPerInvoke = 1000)]
    public async Task ReadWriteAsync()
    {
        for (int i = 0; i < 1000; i++)
        {
            ValueTask<int> read = _client.ReadAsync(_buffer, _cts.Token);
            await _server.WriteAsync(_buffer, _cts.Token);
            await read;
        }
    }
}

Author:	stephentoub
Assignees:	stephentoub
Labels:	area-System.IO
Milestone:	-

[adamsitnik]

LGTM, it's great that the helper components were so easy to re-use. Thanks @stephentoub !