fix SafeFileHandle.CanSeek performance regression

[adamsitnik]

fixes #125660

[adamsitnik]

@EgorBot -windows_intel

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

BenchmarkSwitcher.FromAssembly(typeof(Benchmarks).Assembly).Run(args);

[MemoryDiagnoser]
public class Benchmarks
{
    private string? _filePath;

    [GlobalSetup]
    public void Setup()
    {
        _filePath = Path.GetTempFileName();
        File.WriteAllBytes(_filePath, new byte[1_000]);
    }

    [GlobalCleanup]
    public void Cleanup() => File.Delete(_filePath!);

    [Benchmark]
    public byte[] ReadAllBytes() => File.ReadAllBytes(_filePath!);

    [Benchmark]
    public Task ReadAllBytesAsync() => File.ReadAllBytesAsync(_filePath!);

    [Benchmark]
    public bool OpenAndCanSeek()
    {
        using FileStream handle = File.OpenRead(_filePath!);
        return handle.CanSeek;
    }
}

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[Copilot]

Pull request overview

This PR targets a Windows performance regression in SafeFileHandle.CanSeek / SafeFileHandle.Type usage by avoiding an extra handle-type probe for common disk-file handles.

Changes:

• Adds a GetFileTypeCore fast-path for FILE_TYPE_DISK handles when Path is available, returning RegularFile without calling GetDiskBasedType().

[adamsitnik]

@EgorBot -windows_intel

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

BenchmarkSwitcher.FromAssembly(typeof(Benchmarks).Assembly).Run(args);

[MemoryDiagnoser]
public class Benchmarks
{
    private string? _filePath;

    [GlobalSetup]
    public void Setup()
    {
        _filePath = Path.GetTempFileName();
        File.WriteAllBytes(_filePath, new byte[1_000]);
    }

    [GlobalCleanup]
    public void Cleanup() => File.Delete(_filePath!);

    [Benchmark]
    public byte[] ReadAllBytes() => File.ReadAllBytes(_filePath!);

    [Benchmark]
    public Task ReadAllBytesAsync() => File.ReadAllBytesAsync(_filePath!);

    [Benchmark]
    public bool OpenAndCanSeek()
    {
        using FileStream handle = File.OpenRead(_filePath!);
        return handle.CanSeek;
    }
}

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated no new comments.