Potential for app exit failure when not passing back RunStatus

[skliper]

Describe the bug
CFE_ES_ExitApp reports error when passed in ExitStatus is CFE_ES_RunStatus_APP_RUN.

Typical app pattern (see https://github.com/nasa/sample_app/blob/master/fsw/src/sample_app.c) is:

  while (CFE_ES_RunLoop(&Sample_AppData.RunStatus) == TRUE) {do stuff}
 
  CFE_ES_ExitApp(Sample_AppData.RunStatus);

But CFE_ES_RunLoop does not update RunStatus on internal request to stop:

cFE/fsw/cfe-core/src/es/cfe_es_api.c

Lines 545 to 552 in 7251cbc

	if ( CFE_ES_Global.AppTable[AppID].ControlReq.AppControlRequest != CFE_ES_RunStatus_APP_RUN )
	{
	/*
	** We have an external request to stop
	*/
	ReturnCode = false;
	}

To Reproduce
Steps to reproduce the behavior:

1. Send RestartApp, will error and fail to restart.

Expected behavior
Set passed in RunStatus to the control request for the case above:
RunStatus = CFE_ES_Global.AppTable[AppID].ControlReq.AppControlRequest

Allows the App to take appropriate action.

System observed on:

• cFS Dev Server
• OS: Ubuntu 18.04
• Versions: current dev (6.7.4)

Additional context
Fails build verification testing

Reporter Info
Jacob Hageman - NASA/GSFC

[jphickey]

Is this a recent regression?

From a high level perspective, it seems architecturally kind of odd for ES to keep a status in its internal table, pass it back to an app, which passes it back to ES. ES already knows the status as it is the source of truth anyway. Why does the app need the value anyway?

[skliper]

Is this a recent regression?

It is an issue that was masked by another issue that was fixed in #375. So could have been introduced anytime since 6.6 (I haven't dug into the history).

From a high level perspective, it seems architecturally kind of odd for ES to keep a status in its internal table, pass it back to an app, which passes it back to ES. ES already knows the status as it is the source of truth anyway. Why does the app need the value anyway?

I'm guessing the design pattern is to allow the App to do something based on a request if it wants. Likely "special" cases, maybe a critical app that should never be restarted externally or something. Given the current pattern the app could handle the response and not exit if desired. Maybe @acudmore or @jwilmot have more history?

[jphickey]

There was a different bug in this area - #89 - which addressed an endless loop when CFE_ES_ExitApp was used with unexpected codes. As part of this it restricted the exit status here to be either a normal exit or error exit.

IMO this function should already know that there is a restart request pending - as it is in the ES global state. In this case it shouldn't matter what value the app passes in. The bug is probably here:

cFE/fsw/cfe-core/src/es/cfe_es_api.c

Line 404 in 7251cbc

CFE_ES_Global.AppTable[AppID].ControlReq.AppControlRequest = ExitStatus;

This is overwriting the existing request in the ES internal state, which is probably inadvertently resetting/overwriting the restart request in this case. We should probably only write to the AppControlRequest field if its current value is CFE_ES_RunStatus_APP_RUN, and do not overwrite other values that could be here.

A simple if check around this assignment might fix this.

[skliper]

From @acudmore:

I’m trying to recall the logic of this, but I may have started a little too late before a 3-day weekend. I’ll have to think about it.. but my current thoughts:

Looking at the AppExit code, I think my intention was to allow the app to request an exit through the parameter that it passes in, but maybe a better separation needs to be done with what it is requesting vs the internal app state.

I am having a hard time thinking of why we need to:

• pass the status from ES in the run loop call back to the app
• pass the status from the app to the AppExit call
• have the AppExit call replace the app’s status with what is passed in.

There are a couple of cases for calling the AppExit that I can think of right now:

• The app just falls out of its run loop because it was requested to exit or had an error of some sort – I was told by the system to exit
• The app decides to break out of its run loop and exit – I decided on my own to exit

In the first case, the parameter is not needed, the system already knows why it told the app to exit.
In the second case, the app may wish to inform the system why it decided to exit. In this case it acts more like a parameter, and not the global status.

Is the parameter to AppExit needed at all? If the app is running fine, but has some sort of internal error, or just wants to quit, it may want to indicate why it’s exiting. Otherwise, it might not be needed.

Does that make sense?

[jphickey]

Based on my previous investigation, the CFE_ES_ExitApp call is relevant to distinguish between a voluntary exit that was normal, versus an error of some sort. For all other exit requests, where it is based on a ES command, then ES already knows why the app should be exiting. In particular the app might get an error and decide to exit before it ever reaches the Run Loop part.

My recommendation would be to simplify things:

1. deprecate the in/out status parameter on CFE_ES_RunLoop(). It is already (more or less) a don't care value.
2. Document that when the app exits itself, it should call CFE_ES_AppExit() with either the CFE_ES_RunStatus_APP_EXIT or CFE_ES_RunStatus_APP_ERROR codes to indicate if it is exiting in a normal state or errored state, respectively.

For any other status then ES would already know about it. We just need to make sure the request isn't overwritten (which I think is the cause of this issue).

[skliper]

Sounds good to me. @acudmore?

[jphickey]

There may even be a possibility of further simplification. After another look, even with the distinct exit status (APP_EXIT vs. APP_ERROR) there is not a substantial difference in how its handled during the clean up phase.

The only difference is that it generates a different event (CFE_ES_EXIT_APP_INF_EID vs. CFE_ES_ERREXIT_APP_INF_EID) but otherwise the clean up is identical. Depending on whether this different EID value is useful to anyone, it might be possible to deprecate the CFE_ES_ExitApp() function entirely and simply have a single app exit event.

Note that in the vast majority of FSW applications they run forever, so the only reason they would exit is either from an error or from being commanded to do so. I'm not sure of any real FSW purpose for a non-error, voluntary APP_EXIT status.

[skliper]

Maybe poll the community for any unique use cases? It all sounds good to me as long as people aren't dependent on the behavior. @ejtimmon - any GSFC special use of the exit codes in apps?

[skliper]

Let's discuss this one quickly, also ping @ejtimmon for any concerns w/ suggestion.