terminal: notify when terminal has quit

[marceline-cramer]

Right now, if a process running in a terminal quits, the guest has no way of knowing about it. We have a few ways of fixing this:

• Polling: add a TerminalUpdate variant that polls the terminal for whether it's quit or not. Downside is that we have to continuously poll from whatever owns the terminal, which is ugly and inefficient.
• Subscription: add a TerminalUpdate that subscribes a capability to a message that lets it know when that terminal has quit. Downsides are that it's clunky to implement in the API. We also need to find a way to use the state of a TerminalInstance even though it's being ran as a SinkProcess.
• Killing: somehow wait for the terminal to quit in a separate Tokio thread, then kill the TerminalInstance. We can use down signals to notify processes when the terminal has exited. Downside is that the terminal immediately disappears once it's been killed.

[airidaceae]

If I understand this correctly the TerminalInstance is a guest-side process that wraps around the actual terminal which must run on the host-side to access system resources.

Would there be a way to send a message to the owning process informing it of its death similar to a Monitor system?
Or require a layer of abstraction where there is another process acting as the middle man to the host-side. This process could either be killed directly or poll and then kill itself which would send a message to anything monitoring it making it much easier to handle.

[marceline-cramer]

TerminalRoutine may honestly be the best place to poll terminal death. Each TerminalWrapper could contain an OwnedCapability to its instance that TerminalRoutine may import into a table and kill in order to kill the terminal instance and inform any monitors that the terminal has closed.