Win C# Subprocess does not launch from autologin

Question

This issue has been infuriating me.

I have a C# Windows Forms application (let's call it App) which starts and manages a C++ high-performance executable (let's call it Compute).

So the process tree in the task manager looks like

_App.exe          | CPU | Mem | Disk | Network |
  |_Compute.exe   | CPU | Mem | Disk | Network |

I want the App to run automatically at startup. So far I've tried putting it in the shell-startup directory (can be found by win+R search 'shell:startup') or adding it to the HKeyLocalUser startup part of the registry. I found those solutions on Stackoverflow here.

When testing it out, the App starts just as expected when you log-on or startup the machine. But Compute.exe does not start properly. The process tree looks like:

_App.exe        | CPU | Mem | Disk | Network |
   |_App.exe    |  -  |  -  |   -  |    -    |

It looks like the app is being started as a subprocess of itself, and with no resources. Again - the UI of the parent App starts just fine, is interactable, etc. But it is never able to restart the Compute process - even if forced to by the App process.

I believe it has to do with who starts the App, and that that ownership transfers to the child process. It goes without saying that manually clicking the startup shortcut launches the App and child Compute process no problem.

Any thoughts on what I'm missing here? Thanks for the advice!

When you start compute are you using a relative or full path? — 001, Sep 26 '17 at 03:16
I use the full path via: Directory.GetCurrentDirectory() + mypath — Lukas Schulte, Sep 26 '17 at 03:19
Check the return value from `GetCurrentDirectory`. Is it the...NM. You answered while I was typing this. — 001, Sep 26 '17 at 03:40
Hmm, Process.Start() throws an exception when you provide the wrong path. Don't swallow it, don't try to start the app over and over again. — Hans Passant, Sep 26 '17 at 06:13

score 0 · Answer 1 · answered Sep 26 '17 at 03:38

Okay so this was a learning experience. Thanks to Johnny-Mopp for setting me on the right track.

I was launching the Compute process using

startInfo.FileName = Directory.GetCurrentDirectory() + processName;

This works fine in seemingly all cases but the start-on-login case described.

There is another, more explicit option which starts Compute process from the parent-process App's directory like so:

startInfo.FileName = Path.GetDirectoryName(Assembly.GetExecutingAssembly().Location) + processName;

This works in when starting the Compute process from the parent App on-startup, at-login. Phew.

Win C# Subprocess does not launch from autologin

1 Answers1