fix SafeFileHandle.CanSeek performance regression#125807
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adamsitnik merged 5 commits intomainfrom Mar 21, 2026
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@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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Tagging subscribers to this area: @dotnet/area-system-io |
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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
GetFileTypeCorefast-path forFILE_TYPE_DISKhandles whenPathis available, returningRegularFilewithout callingGetDiskBasedType().
src/libraries/System.Private.CoreLib/src/Microsoft/Win32/SafeHandles/SafeFileHandle.Windows.cs
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This was referenced Mar 20, 2026
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- use existing public API for opening directories as SafeFileHandle to ensure we have test coverage for it - make sure NoBuffering and BackupOrRestore are not defined in multiple places - fix the bug - remove volatile
Member
Author
|
@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;
}
} |
src/libraries/System.Private.CoreLib/src/Microsoft/Win32/SafeHandles/SafeFileHandle.Windows.cs
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danmoseley
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Mar 20, 2026
src/libraries/System.Private.CoreLib/src/System/IO/Strategies/FileStreamHelpers.cs
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danmoseley
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Mar 20, 2026
...raries/System.Runtime/tests/System.IO.FileSystem.Tests/SafeFileHandle/GetFileType.Windows.cs
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src/libraries/System.Private.CoreLib/src/Microsoft/Win32/SafeHandles/SafeFileHandle.Windows.cs
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danmoseley
approved these changes
Mar 20, 2026
stephentoub
approved these changes
Mar 20, 2026
Co-authored-by: Dan Moseley <[email protected]>
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fixes #125660