Avoid encoding unchanged process environments on Unix

[Copilot]

Unix process startup now passes a null environment pointer when ProcessStartInfo.Environment remains untouched, avoiding dictionary creation and UTF-8 encoding.

• Native process creation resolves null to environ.
• Explicit ProcessStartInfo environment changes retain existing encoding behavior.
• Process-wide environment mutations continue using a managed snapshot to preserve semantics.
• Added coverage for lazy environment inheritance.

Note

This description was generated with GitHub Copilot.

[azure-pipelines]

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[adamsitnik]

@copilot address my feedback

[adamsitnik]

@copilot address my feedback

[adamsitnik]

@EgorBot -osx_arm64 -linux_x64

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System.Diagnostics;

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

[MemoryDiagnoser]
public class Benchmarks
{
    private static ProcessStartInfo s_startProcessStartInfo = new ProcessStartInfo()
    {
        FileName = "whoami", // exists on both Windows and Unix, and has very short output
        RedirectStandardOutput = true // avoid visible output
    };

    private Process? _startedProcess;

    [Benchmark]
    public void Start()
    {
        _startedProcess = Process.Start(s_startProcessStartInfo)!;
    }

    [IterationCleanup(Target = nameof(Start))]
    public void CleanupStart()
    {
        if (_startedProcess != null)
        {
            _startedProcess.WaitForExit();
            _startedProcess.Dispose();
            _startedProcess = null;
        }
    }

    [Benchmark]
    public void StartAndWaitForExit()
    {
        using (Process p = Process.Start(s_startProcessStartInfo)!)
        {
            p.WaitForExit();
        }
    }
}

[Copilot]

@copilot address my feedback

Addressed the remaining test feedback in 73ed42b7; targeted System.Diagnostics.Process tests pass (637 total, 0 failures).

[adamsitnik]

@copilot address my feedback

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

[azure-pipelines]

Azure Pipelines:
Successfully started running 3 pipeline(s).
12 pipeline(s) were filtered out due to trigger conditions.
There may be pipelines that require an authorized user to comment /azp run to run.

[adamsitnik]

to other reviewers: this logic is part of Environment.Unix.cs rather than Environment.Variables.Unix.cs because, the latter is used only for Mono (or at least not for CLR):

runtime/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

Line 2683 in 402ed14

<Compile Include="$(MSBuildThisFileDirectory)System\Environment.Variables.Unix.cs" Condition="'$(FeatureCoreCLR)' != 'true'" />

As it seems that for CLR we compile Environment.Variables.Windows.cs on UNIX!!!

runtime/src/libraries/System.Private.CoreLib/src/System.Private.CoreLib.Shared.projitems

Lines 2412 to 2426 in 402ed14

	<ItemGroup Condition="'$(TargetsWindows)' == 'true' or '$(FeatureCoreCLR)'=='true'">
	<Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.GetEnvironmentVariable.cs">
	<Link>Common\Interop\Windows\Kernel32\Interop.GetEnvironmentVariable.cs</Link>
	</Compile>
	<Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.GetEnvironmentStrings.cs">
	<Link>Common\Interop\Windows\Kernel32\Interop.GetEnvironmentStrings.cs</Link>
	</Compile>
	<Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.FreeEnvironmentStrings.cs">
	<Link>Common\Interop\Windows\Kernel32\Interop.FreeEnvironmentStrings.cs</Link>
	</Compile>
	<Compile Include="$(CommonPath)Interop\Windows\Kernel32\Interop.SetEnvironmentVariable.cs">
	<Link>Common\Interop\Windows\Kernel32\Interop.SetEnvironmentVariable.cs</Link>
	</Compile>
	<Compile Include="$(MSBuildThisFileDirectory)System\Environment.Variables.Windows.cs" />
	</ItemGroup>

[adamsitnik]

@EgorBot -osx_arm64 -linux_x64

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System.Diagnostics;

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

[MemoryDiagnoser]
public class Benchmarks
{
    private static ProcessStartInfo s_startProcessStartInfo = new ProcessStartInfo()
    {
        FileName = "whoami", // exists on both Windows and Unix, and has very short output
        RedirectStandardOutput = true // avoid visible output
    };

    private Process? _startedProcess;

    [Benchmark]
    public void Start()
    {
        _startedProcess = Process.Start(s_startProcessStartInfo)!;
    }

    [IterationCleanup(Target = nameof(Start))]
    public void CleanupStart()
    {
        if (_startedProcess != null)
        {
            _startedProcess.WaitForExit();
            _startedProcess.Dispose();
            _startedProcess = null;
        }
    }

    [Benchmark]
    public void StartAndWaitForExit()
    {
        using (Process p = Process.Start(s_startProcessStartInfo)!)
        {
            p.WaitForExit();
        }
    }
}

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

[adamsitnik]

@EgorBot -osx_arm64 -linux_x64

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System.Diagnostics;

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

[MemoryDiagnoser]
public class Benchmarks
{
    private static ProcessStartInfo s_startProcessStartInfo = new ProcessStartInfo()
    {
        FileName = "whoami", // exists on both Windows and Unix, and has very short output
        RedirectStandardOutput = true // avoid visible output
    };

    private Process? _startedProcess;

    [Benchmark]
    public void Start()
    {
        _startedProcess = Process.Start(s_startProcessStartInfo)!;
    }

    [IterationCleanup(Target = nameof(Start))]
    public void CleanupStart()
    {
        if (_startedProcess != null)
        {
            _startedProcess.WaitForExit();
            _startedProcess.Dispose();
            _startedProcess = null;
        }
    }

    [Benchmark]
    public void StartAndWaitForExit()
    {
        using (Process p = Process.Start(s_startProcessStartInfo)!)
        {
            p.WaitForExit();
        }
    }
}

[Copilot]

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

[adamsitnik]

@EgorBot -osx_arm64 -linux_x64

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Engines;
using BenchmarkDotNet.Running;
using Microsoft.Win32.SafeHandles;
using System;
using System.Diagnostics;
using System.IO;
using System.Text;
using System.Threading.Tasks;

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

[MemoryDiagnoser]
[SimpleJob(launchCount:5, warmupCount:1, iterationCount:100, invocationCount: 1), JitTiering(JitTieringMode.Skip)]
public class DefaultEnvVars
{
    private static readonly SafeFileHandle s_nullHandle = File.OpenNullHandle();
    private static ProcessStartInfo s_startProcessStartInfo = new ProcessStartInfo()
    {
        FileName = "whoami", // exists on both Windows and Unix, and has very short output
        StandardInputHandle = s_nullHandle,
        StandardOutputHandle = s_nullHandle,
        StandardErrorHandle = s_nullHandle,
    };

    private Process? _startedProcess;

    [Benchmark]
    public void Start() => _startedProcess = Process.Start(s_startProcessStartInfo)!;

    [IterationCleanup(Target = nameof(Start))]
    public void CleanupStart()
    {
        if (_startedProcess != null)
        {
            _startedProcess.WaitForExit();
            _startedProcess.Dispose();
            _startedProcess = null;
        }
    }

    [Benchmark]
    public int Run() => Process.Run(s_startProcessStartInfo).ExitCode;

    [GlobalCleanup]
    public void Cleanup() => s_nullHandle.Dispose();
}

[adamsitnik]

@jkotas I've converted it to a draft again, as the benchmarks show regressions in some cases and I simply need to run them locally and profile if needed. Please ignore this PR for now.

[adamsitnik]

@EgorBot -osx_arm64 -linux_x64

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Engines;
using BenchmarkDotNet.Running;
using Microsoft.Win32.SafeHandles;
using System;
using System.Diagnostics;
using System.IO;
using System.Text;
using System.Threading.Tasks;

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

[MemoryDiagnoser]
public class DefaultEnvVars
{
    private static readonly SafeFileHandle s_nullHandle = File.OpenNullHandle();
    private static ProcessStartInfo s_startProcessStartInfo = new ProcessStartInfo()
    {
        FileName = "whoami", // exists on both Windows and Unix, and has very short output
        StandardInputHandle = s_nullHandle,
        StandardOutputHandle = s_nullHandle,
        StandardErrorHandle = s_nullHandle,
    };

    private Process? _startedProcess;

    [Benchmark]
    public void Start() => _startedProcess = Process.Start(s_startProcessStartInfo)!;

    [IterationCleanup(Target = nameof(Start))]
    public void CleanupStart()
    {
        if (_startedProcess != null)
        {
            _startedProcess.WaitForExit();
            _startedProcess.Dispose();
            _startedProcess = null;
        }
    }

    [Benchmark]
    public int Run() => Process.Run(s_startProcessStartInfo).ExitCode;

    [GlobalCleanup]
    public void Cleanup() => s_nullHandle.Dispose();
}

[adamsitnik]

@EgorBot -osx_arm64 -linux_x64

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Engines;
using BenchmarkDotNet.Running;
using Microsoft.Win32.SafeHandles;
using System;
using System.Diagnostics;
using System.IO;
using System.Text;
using System.Threading.Tasks;

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

[MemoryDiagnoser]
public class DefaultEnvVars
{
    private static readonly SafeFileHandle s_nullHandle = File.OpenNullHandle();
    private static ProcessStartInfo s_startProcessStartInfo = new ProcessStartInfo()
    {
        FileName = "whoami", // exists on both Windows and Unix, and has very short output
        StandardInputHandle = s_nullHandle,
        StandardOutputHandle = s_nullHandle,
        StandardErrorHandle = s_nullHandle,
    };

    private Process? _startedProcess;

    [Benchmark]
    public void Start() => _startedProcess = Process.Start(s_startProcessStartInfo)!;

    [IterationCleanup(Target = nameof(Start))]
    public void CleanupStart()
    {
        if (_startedProcess != null)
        {
            _startedProcess.WaitForExit();
            _startedProcess.Dispose();
            _startedProcess = null;
        }
    }

    [Benchmark]
    public int Run() => Process.Run(s_startProcessStartInfo).ExitCode;

    [GlobalCleanup]
    public void Cleanup() => s_nullHandle.Dispose();
}

[adamsitnik]

The benchmarks don't show an obvious win. There seems to be always a regression on macOS and sometimes a win on Linux. So the benchmark can be simply bimodal.