System.Diagnostics.Process with CreateNoWindow does not redirect stdout/stderr to parent process

[mxschmitt]

Description

When using System.Diagnostics.Process with CreateNoWindow = true the output does not get redirected to the parent process. It will end up in no output.

The docs don't say anything about this behaviour, thats why I'm opening this issue and CreateNoWindow changes the behaviour if stdout/err gets redirected or not.

Reproduction Steps

using System.Diagnostics;

if (args.Length >= 1 && args[0] == "--start-process")
{
    var currentExecutable = Environment.ProcessPath;
    if (currentExecutable == null)
    {
        Console.Error.WriteLine("Could not get current executable path");
        return;
    }
    var playwrightStartInfo = new ProcessStartInfo(currentExecutable)
    {
        UseShellExecute = false,
        RedirectStandardError = false,
        RedirectStandardOutput = false,
        CreateNoWindow = true,
    };

    using var pwProcess = new Process()
    {
        StartInfo = playwrightStartInfo,
    };

    pwProcess.Start();
    pwProcess.WaitForExit();
}
else
{
    Console.WriteLine("Hello stdout!");
    Console.Error.WriteLine("Hello stderr!");
}

Run it with ./bin/Debug/net6.0/dotnetrepro.exe --start-process.

Expected behavior

Hello stderr! and Hello stdout! are getting printed.

Actual behavior

They get not printed.

Regression?

No response

Known Workarounds

Remove CreateNoWindow = true.

or:

Using RedirectStandardError = true and RedirectStandardOutput = true and manually redirecting it to the parent stdout/stderr.

Configuration

I can only reproduce it on Windows 10 + 11 amd64.

Other information

PS C:\Users\maxsc\Desktop\dotnet-process-redirect-issue> dotnet --list-sdks
6.0.102 [C:\Program Files\dotnet\sdk]

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

Issue Details

---

Description

When using System.Diagnostics.Process with CreateNoWindow = true the output does not get redirected to the parent process. It will end up in no output.

Reproduction Steps

using System.Diagnostics;

if (args.Length >= 1 && args[0] == "--start-process")
{
    var currentExecutable = Environment.ProcessPath;
    if (currentExecutable == null)
    {
        Console.Error.WriteLine("Could not get current executable path");
        return;
    }
    var playwrightStartInfo = new ProcessStartInfo(currentExecutable)
    {
        UseShellExecute = false,
        RedirectStandardError = false,
        RedirectStandardOutput = false,
        CreateNoWindow = true,
    };

    using var pwProcess = new Process()
    {
        StartInfo = playwrightStartInfo,
    };

    pwProcess.Start();
    pwProcess.WaitForExit();
}
else
{
    Console.WriteLine("Hello stdout!");
    Console.Error.WriteLine("Hello stderr!");
}

Run it with ./bin/Debug/net6.0/dotnetrepro.exe --start-process.

Expected behavior

Hello stderr! and Hello stdout! are getting printed.

Actual behavior

They get not printed.

Regression?

No response

Known Workarounds

Remove CreateNoWindow = true.

or:

Using RedirectStandardError = true and RedirectStandardOutput = true and manually redirecting it to the parent stdout/stderr.

Configuration

I can only reproduce it on Windows 10 + 11 amd64.

Other information

PS C:\Users\maxsc\Desktop\dotnet-process-redirect-issue> dotnet --list-sdks
6.0.102 [C:\Program Files\dotnet\sdk]

Author:	mxschmitt
Assignees:	-
Labels:	area-System.Diagnostics.Process, untriaged
Milestone:	-

[deeprobin]

Does it work with UseShellExecute = true?

ShellExecute uses a different routine to start the process on windows.

runtime/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/Process.Win32.cs

Lines 25 to 27 in 1e41844

	return startInfo.UseShellExecute
	? StartWithShellExecuteEx(startInfo)
	: StartWithCreateProcess(startInfo);

For reference:

• using Shell Execute
• using CreateProcess

[jozkee]

From https://docs.microsoft.com/en-us/windows/win32/procthread/process-creation-flags

The process is a console application that is being run without a console window. Therefore, the console handle for the application is not set.

There's no console to write to when the option is set. Expecting output from Console.WriteLine in this case doesn't seem reasonable. What are you trying to achieve?

[mxschmitt]

From https://docs.microsoft.com/en-us/windows/win32/procthread/process-creation-flags

The process is a console application that is being run without a console window. Therefore, the console handle for the application is not set.

There's no console to write to when the option is set. Expecting output from Console.WriteLine in this case doesn't seem reasonable. What are you trying to achieve?

Interesting! The use-case of it is that we spawn a Program in .NET, which internally does wrap another program as a subprocess. There we want to inherit all the stdout/stderr. This is working as expected when setting RedirectStandardOutput=false, except that a dedicated window is shown when the user is trying to call this Program API inside their C# code (downstream issue: microsoft/playwright-dotnet#2103). So we had then three options:

a) RedirectStandardOutput=true -> we need to manually redirect them and it has side effects (aka Node.js isTTY = false)
b) RedirectStandardOutput=false CreateNoWindow=false -> a dedicated window gets shown in some edge cases (microsoft/playwright-dotnet#2103)
c) RedirectStandardOutput=false CreateNoWindow=true -> no output gets shown anymore, thats what the bug is about.

Ideal solution would be c) in my opinion. Or how do you see it?

[rhuijben]

Ideal solution would be c) in my opinion. Or how do you see it?

That would be a completely breaking change if you just expect to run the program, handing over the user interaction until the subprocess finishes.

Your usecase somehow needs hooking up stout and/or studeer to a null device, if you want to go the output nowhere.