Plugins started on unsuccessful task start are not stopped

[geauxvirtual]

After creating a task, if the task is stopped and a plugin is removed that the task needs, attempting to start the task will result in starting the plugins required for the task, but not stopping those plugins when the task fails to start due to a missing required plugin. There is no way to stop these plugins without stopping snapd.

[lynxbat]

Would a plugin existence check on start solve this?

[geauxvirtual]

Code currently tries to subscribe to dependencies and then tries to unsubscribe from dependencies if any error is found during subscription. This doesn't look to be stopping the started plugins though.

https://github.com/intelsdi-x/snap/blob/master/scheduler/scheduler.go#L486-L510

[geauxvirtual]

I believe the problems lies here https://github.com/intelsdi-x/snap/blob/master/scheduler/scheduler.go#L500. We are ranging over subbedDeps, but nothing actually sets subbedDeps, so this slice is empty.

[geauxvirtual]

To expand on the last comment, there is only one dependency group created for the task. subbedDeps is only added to if all subscriptions succeed. If an error occurs during subscription of dependencies, then the code tries to iterate over subbedDeps which has not been added to yet.

[lynxbat]

Nice catch