[API Proposal]: ProcessStartInfo.CreateSuspended, Process.Resume

[sebastienros]

Background and motivation

Currently I use ProcessStartInfo/Process.Start to launch processes with overridden environment variables, redirect standard input and output, and so forth.

I now need to use the CREATE_SUSPENDED flag so that I can modify the process after it's created and before it starts actual execution, but there's no way to pass this flag into ProcessStartInfo/Process.Start. Given that I still need to use all the other features of ProcessStartInfo, the only reasonable path I can see forward is to either copy or reimplement the entirety of the System.Diagnostics.Process code.

My proposal would also be cross-platform.

API Proposal

namespace System.Diagnostics
{
    public sealed class ProcessStartInfo
    {
        public bool StartSuspended { get; set; } // name follows the pattern established by StartDetached
    }
}

namespace Microsoft.Win32.SafeHandles
{
    public sealed class SafeProcessHandle
    {
        public void Resume(); // already approved in https://github.com/dotnet/runtime/issues/123380#issuecomment-3880499825
    }
}

API Usage

var process = new Process()
{
    StartInfo = {
        FileName = executable,
        StartSuspended = true,
        CreateNoWindow = true, // for reference only, as it has the same characteristics
    }
};

process.Start();

int currentPriority = getpriority(PRIO_PROCESS, process.Id);
setpriority(PRIO_PROCESS, process.Id, currentPriority + 1);

process.SafeHandle.Resume();

Alternative Designs

The initial proposal included CreateSuspended name, but it's inconsistent with StartDetached (#124334).

An alternative to having Resume method is to extend SafeProcessHandle.Signal with an ability to map PosixSignal.SIGCONT to ResumeThread on Windows.

namespace System.Runtime.InteropServices
{
    public enum PosixSignal
    {
-       [UnsupportedOSPlatform("windows")]
        SIGCONT = -6,
    }
}

I don't think these issues are duplicates since they adopt a different design that doesn't seem to get traction.

#71515
#90581

NB: @hach-que I copied your proposal and tried to make the API easier to get through the review process.

Risks

No response

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Issue Details

---

Background and motivation

Currently I use ProcessStartInfo/Process.Start to launch processes with overridden environment variables, redirect standard input and output, and so forth.

I now need to use the CREATE_SUSPENDED flag so that I can modify the process after it's created and before it starts actual execution, but there's no way to pass this flag into ProcessStartInfo/Process.Start. Given that I still need to use all the other features of ProcessStartInfo, the only reasonable path I can see forward is to either copy or reimplement the entirety of the System.Diagnostics.Process code.

My proposal would also be cross-platform.

API Proposal

namespace System.Diagnostics;

public sealed partial class ProcessStartInfo
{
    public bool CreateSuspended { get; set; }
}

public partial class Process
{
    public bool Resume();
}

API Usage

var process = new Process()
{
    StartInfo = {
        FileName = executable,
        CreateSuspended = true,
        CreateNoWindow = true, // for reference only, as it has the same characteristics
    }
};

process.Start();

// Do whatever is needed with the process...

process.Resume();

Alternative Designs

I don't think these issues are duplicates since they adopt a different design that doesn't seem to get traction.

#71515
#90581

NB: @hach-que I copied your proposal and tried to make the API easier to get through the review process.

Risks

No response

Author:	sebastienros
Assignees:	-
Labels:	api-suggestion, area-System.Diagnostics.Process, untriaged
Milestone:	-

[alexrp]

To be clear, it's not that #71515 didn't have traction. The discussion landed on exposing "proper" properties for the various flags and options related to process creation (as you've done for bool CreateSuspended here), but the proposal should include all/most of the Windows process creation options so that API review can have a more complete picture of how the API might look later down the line, even if only parts of it are implemented initially. I just haven't had time to do that yet...

[adamsitnik]

As an end user, I would be happy to have it and use it in BenchmarkDotNet for some of the profiler plugins (cc @lihaMSFT)

As a maintainer I need to know whether it would be possible to implement it on Unix? (cc @tmds)

[jborean93]

Just to add my 2 cents, this should be the last remaining feature that is needed by PowerShell to move away from custom PInvoke code to using System.Diagnostics.Process for all scenarios. Currently they rely on being able to create a suspended process so that they can configure a Job object of that new process before they resume it. Being able to use S.D.Process directly would be great as it solves other problems like not being able to create the Process object with an all access token from the one PowerShell spawned through CreateProcess*.

[adamsitnik]

Currently they rely on being able to create a suspended process so that they can configure a Job object of that new process before they resume it.

@jborean93 Why PowerShell configures a Job object? I am asking because if they do that just to be able to kill the process on parent death, we could achieve that with a different API: #101985