servstate: close service ring buffer on process exit during stop

[sundeep8967]

Problem

When a service is stopped by the service manager, its log ring buffer was left open. Any log puller or reader iterators would wait until forced termination deadlines or remain open while the service was inactive. Furthermore, attempting to close ring buffers globally in LogManager.Stop() risks closing buffers for services that could still be running.

Solution

• internals/overlord/servstate/handlers.go:
  • In s.exited(), close s.logs (_ = s.logs.Close()) when the service reaches stateStopped after its process has exited.
  • In s.stop(), close s.logs when the service is stopped while in stateBackoff.
  • In serviceForStart(), allocate a fresh s.logs = servicelog.NewRingBuffer(maxLogBytes) if the service is subsequently restarted and the previous buffer was closed.
• internals/overlord/servstate/export_test.go:
  • Export ServiceLogBuffer helper for test verification.
• internals/overlord/servstate/manager_test.go:
  • Add assertions to TestStartStopServices and TestStopDuringBackoff to verify s.logs.Closed() is true after stopping.
• internals/overlord/logstate/manager_test.go:
  • Fix a pre-existing goroutine leak in TestLabels by calling m.Stop() at the end of the test.

Fixes #681

Testing

• Verified compilation on Linux (GOOS=linux go test -c ./internals/overlord/servstate).
• Tested TestStartStopServices and TestStopDuringBackoff with ring buffer closure assertions.
• Verified internals/overlord/logstate tests (TestTimelyShutdown, TestLabels, TestPlanChange).

[hpidcock]

Hi @sundeep8967,

Thank-you for the PR. It looks like we are trying to close the ring buffers for services that could still be running.
We need to have the service manager close the ring buffer during stop once the process has exited.

[sundeep8967]

Hi @hpidcock,

Thank you for the review and guidance!

I have updated the implementation according to your feedback:

• Reverted closing all buffers globally in LogManager.Stop().
• Updated servstate so the service manager closes the service log ring buffer (s.logs.Close()) during stop once the process has exited in s.exited() (and in s.stop() when stopped during backoff).
• Added logic in serviceForStart() to allocate a fresh ring buffer if the service is restarted after being stopped.
• Added unit test assertions in TestStartStopServices and TestStopDuringBackoff to verify the ring buffer is closed when the service stops.

Please take another look when you have a moment.