StartProcess Mystery

[CharliePoole]

It appears that StartProcess has spontaneously started acting differently in my code. Of course, I doubt that's the case - I probably did something in my own code - but I can't figure out what.

What is happening is that I call StartProcess(FileName, ProcessSettings) and the process starts (It's a GUI so I can see it running) but the next line of code executes immediately. Since that line is looking for the output file created by the process, it fails.

Looking for any ideas on how or why this is happening or on how to debug it.

[augustoproiete]

Hey @CharliePoole nothing has changed in StartProcess in recent versions of cake. It still waits for the process to finish, before it continues execution.

You can prove this by executing notepad.exe on Windows, for example:

// test-startprocess-notepad.cake

var exitCode = StartProcess("notepad.exe");

Information("I don't see this until I close notepad");
Information("notepad exit code: {0}", exitCode);

I suspect that something changed with the executable that you are calling. It's likely that the executable is behaving like a bootstrapper, in the sense that it's launching another executable, and then finishes its execution.

e.g. You call myapp.exe, then internally myapp.exe starts another process myapp-123.exe without waiting for myapp-123.exe to finish its execution.

If that's the case, you'd need to find out what's the end process that needs to be executed, and call that instead (skipping this "launcher" app).

---

ps: If you want, you can be more explicit about waiting for the process to end, but I'd expect you'll end up with the same result, unless you call the final app you want to run:

var exitCode = -1;
using (var process = StartAndReturnProcess("notepad.exe"))
{
    process.WaitForExit();
    exitCode = process.GetExitCode();
}

Information("Exit code: {0}", exitCode);
// ...

[CharliePoole]

@augustoproiete Thanks for your response. In fact, I did try the alternative you suggest, with the same result.

I have concluded that there is some race condition in my application, so that the main process is terminating before all the work (done in a child process) has completed. However, I am only working on the Cake script, so something I have done there is exposing the race condition, which was not visible before. IOW, still some remote chance of a Cake bug but probably not. :-)

I'm now re-applying all my changes in smaller steps to see if I can figure out how this happened.

[CharliePoole]

@augustoproiete BTW... excellent guess about the app being a launcher of another process, although it's a bit more than that. The app is my TestCentric GUI test runner for NUnit tests. It launches, controls and displays output from multiple agent processes, which actually run the tests. It is, in fact terminating early... before all the work is done... but only when run in my CI script.

[augustoproiete]

@CharliePoole Glad to see you got to the bottom of it!

[CharliePoole]

@augustoproiete Well, surprisingly, that was not it. Here is a snippet of code I am using to launch the Gui in order to run its own tests.

string executablePath = BuildSettings.OutputDirectory + "testcentric.exe"; // Works correctly
//string executablePath = "testcentric.exe"; // Returns prematurely

return BuildSettings.Context.StartProcess(executablePath, new ProcessSettings()
{
	Arguments = arguments,
	WorkingDirectory = BuildSettings.OutputDirectory
});

The uncommented line gives an absolute path and the call to StartProcess does not return until the process exits. But if I uncomment the relative path, it returns immediately.

The same thing happens if I use FilePaths rather than strings or if I use the longer form to return a process and wait for it to complete.

This is using Cake.Tool 2.3.0, which is pretty mature, so... surprising. :-)

I have a workaround now, which is to only set the absolute path when I am running, because BuildSettings is guaranteed to be competely initialized at that point. Do you want an issue for this?