Do not create new terminals when launching process on Windows with --no-stdio

[xbolva00]

Summary

Partially fixes PR38222

[labath]

I think the issue here is that on windows we don't have the ability(*) to pipe stdio through lldb, so if you create a process without a console, you will not be able to use see it's output or pass it some input (probably fine for gui apps, but bad for console ones). This means your approach will also make things inconsistent with other platforms, only in a different way. (I don't really have an opinion which one is better/worse.)

(*) I think there is a way to emulate the unix pty behavior on windows, but it is not exactly straight-forward. It involves creating a hidden console and then polling that for changes/keypresses (I don't know the details, but that's how someone once explained it to me).

[xbolva00]

In D51966#1231533, @labath wrote:

I think the issue here is that on windows we don't have the ability(*) to pipe stdio through lldb, so if you create a process without a console, you will not be able to use see it's output or pass it some input (probably fine for gui apps, but bad for console ones). This means your approach will also make things inconsistent with other platforms, only in a different way. (I don't really have an opinion which one is better/worse.)

(*) I think there is a way to emulate the unix pty behavior on windows, but it is not exactly straight-forward. It involves creating a hidden console and then polling that for changes/keypresses (I don't know the details, but that's how someone once explained it to me).

Ok, thanks for info!

[clayborg]

We should obey the --tty option here and set CREATE_NEW_CONSOLE if it is set no?

[xbolva00]

In D51966#1231943, @clayborg wrote:

We should obey the --tty option here and set CREATE_NEW_CONSOLE if it is set no?

I also thought about it and I am in favour of this solution. Suggestions welcome, especially from @zturner, @labath, @JDevlieghere , @teemperor, ..

[clayborg]

The other option is to only remove this flag if "--no-stdio" is set.

The best solution IMHO is:

• find a way to get stdio from a process and feed to to LLDB so it shows up when neither --tty nor --no-stdio is set
• when --tty is specified, set the CREATE_NEW_CONSOLE bit
• when --no-stdio is specified, don't get stdio from child process and don't set CREATE_NEW_CONSOLE

[xbolva00]

So basically the hardest problem is to "find a way to get stdio from a process and feed to to LLDB so it shows up when neither --tty nor --no-stdio is set" ..

[clayborg]

In D51966#1232057, @xbolva00 wrote:

So basically the hardest problem is to "find a way to get stdio from a process and feed to to LLDB so it shows up when neither --tty nor --no-stdio is set" ..

yes. The easier solution is to just create a console for now if this is too hard. So the fix here would be to just not set the CREATE_NEW_CONSOLE if --no-stdio is set.

[labath]

This makes sense to me, but the windows folks should say what is best for their platform.

[zturner]

I'm fine with this.

source/Host/windows/ProcessLauncherWindows.cpp

if (hide_console_var &&
     startupinfo.dwFlags |= STARTF_USESHOWWINDOW;
     startupinfo.wShowWindow = SW_HIDE;
   }
 
   DWORD flags = CREATE_NEW_CONSOLE | CREATE_UNICODE_ENVIRONMENT;
   if (launch_info.GetFlags().Test(eLaunchFlagDebug))
     flags |= DEBUG_ONLY_THIS_PROCESS;
 
+  if (launch_info.GetFlags().Test(eLaunchFlagDisableSTDIO))
+    flags &= ~CREATE_NEW_CONSOLE;
+
   LPVOID env_block = nullptr;
   ::CreateEnvironmentBuffer(launch_info.GetEnvironment(), environment);
   if (!environment.empty())
     env_block = environment.data();
 
   executable = launch_info.GetExecutableFile().GetPath();
   launch_info.GetArguments().GetQuotedCommandString(commandLine);