Add service manager infrastructure (#14150)

* Add service manager infrastructure

The changes are (This will be a bit long):
- A ServiceManager class that spawns a background thread and deals with
  service lifecycle management. The idea is that service lifecycle code
  will run in async functions, so a single thread is enough to manage
  any (reasonable) amount of services.

- A Service class, that offers start(), stop() and restart() methods
  that simply notify the service manager to... well. Start, stop or
  restart a service.

(!) Warning: Note that this differs from mp.Process.start/stop in that
  the service commands are sent asynchronously and will complete
  "eventually". This is good because it means that business logic is
  fast when booting up and shutting down, but we need to make sure
  that code does not rely on start() and stop() being instant
  (Mainly pid assignments).

  Subclasses of the Service class should use the on_start and on_stop
  methods to monitor for service events. These will be run by the
  service manager thread, so we need to be careful not to block
  execution here. Standard async stuff.

(!) Note on service names: Service names should be unique within a
  ServiceManager. Make sure that you pass the name you want to
  super().__init__(name="...") if you plan to spawn multiple instances
  of a service.

- A ServiceProcess class: A Service that wraps a multiprocessing.Process
  into a Service. It offers a run() method subclasses can override and
  can support in-place restarting using the service manager.

And finally, I lied a bit about this whole thing using a single thread.
I can't find any way to run python multiprocessing in async, so there is
a MultiprocessingWaiter thread that waits for multiprocessing events and
notifies any pending futures. This was uhhh... fun? No, not really.
But it works. Using this part of the code just involves calling the
provided wait method. See the implementation of ServiceProcess for more
details.

Mirror util.Process hooks onto service process

Remove Service.__name attribute

Do not serialize process object on ServiceProcess start.

asd

* Update frigate dictionary

* Convert AudioProcessor to service process

frigate/app.py

@@ -63,6 +63,7 @@ from frigate.record.cleanup import RecordingCleanup
 from frigate.record.export import migrate_exports
 from frigate.record.record import manage_recordings
 from frigate.review.review import manage_review_segments
+from frigate.service_manager import ServiceManager
 from frigate.stats.emitter import StatsEmitter
 from frigate.stats.util import stats_init
 from frigate.storage import StorageMaintainer
@@ -78,7 +79,6 @@ logger = logging.getLogger(__name__)
 
 class FrigateApp:
     def __init__(self, config: FrigateConfig) -> None:
-        self.audio_process: Optional[mp.Process] = None
         self.stop_event: MpEvent = mp.Event()
         self.detection_queue: Queue = mp.Queue()
         self.detectors: dict[str, ObjectDetectProcess] = {}
@@ -449,9 +449,8 @@ class FrigateApp:
         ]
 
         if audio_cameras:
-            self.audio_process = AudioProcessor(audio_cameras, self.camera_metrics)
-            self.audio_process.start()
-            self.processes["audio_detector"] = self.audio_process.pid or 0
+            proc = AudioProcessor(audio_cameras, self.camera_metrics).start(wait=True)
+            self.processes["audio_detector"] = proc.pid or 0
 
     def start_timeline_processor(self) -> None:
         self.timeline_processor = TimelineProcessor(
@@ -639,11 +638,6 @@ class FrigateApp:
             ReviewSegment.end_time == None
         ).execute()
 
-        # stop the audio process
-        if self.audio_process:
-            self.audio_process.terminate()
-            self.audio_process.join()
-
         # ensure the capture processes are done
         for camera, metrics in self.camera_metrics.items():
             capture_process = metrics.capture_process
@@ -712,4 +706,6 @@ class FrigateApp:
             shm.close()
             shm.unlink()
 
+        ServiceManager.current().shutdown(wait=True)
+
         os._exit(os.EX_OK)