Keep frame shared memory mapped (#24644)

* keep frame shm open and skip overwritten frames

Every reader closed and reopened a frame's shared memory segment on each frame, so each process paid a page fault on every page of a fresh mapping (about 760 for a 1080p frame) per frame. Readers now keep segments mapped. Capture stamps each slot's frame time in a per-camera `{camera}_frame_times` segment, and `get()` returns None when the slot no longer holds the requested frame, reopening once by name so a mapping left over from a same-size camera recreate heals itself. Capture also reuses a slot when the frame queue is full, since no reader was told about it.

* verify the frame for embeddings object updates

Tracked object events only carried the object's own frame_time, which stays at its last detection when the object isn't detected in a frame, so embeddings couldn't check the slot it read and could crop face or plate data from a frame that had already been overwritten. Events now carry the time of the frame they name, and embeddings passes it to `get()`.

* log when a frame slot was overwritten before it was read

A lapped read and a missing segment ended up as the same debug line at every caller, so there was no way to tell a slow reader from a missing frame.

* bring the FrameManager interface in line with its implementation

The abstract get() still had a timeout_ms signature from an older implementation and frame_times() wasn't declared, though capture and detect are typed against the interface. get() also didn't say how long the array it returns stays valid.

* drop a camera's cached frame mappings when it is removed or recreated

A reader that kept its mappings open stayed on a removed camera's segments, which pinned their shared memory until restart, and after a same-size recreate the ledger reopen only refreshed the slot being read while the other cached slots still returned the old camera's pixels. Readers now drop every cached slot for a camera on its remove update, and get() does the same when a ledger mismatch turns out to be a replaced ledger rather than a lapped slot.

* match a camera's frame names exactly in close_camera

The prefix match on `{camera}_frame` also caught another camera whose name starts with it, so removing `cam` dropped the cached ring of a camera named `cam_frame`.

frigate/output/output.py

@@ -145,6 +145,7 @@ class OutputProcess(FrigateProcess):
                 CameraConfigUpdateEnum.birdseye,
                 CameraConfigUpdateEnum.enabled,
                 CameraConfigUpdateEnum.record,
+                CameraConfigUpdateEnum.remove,
             ],
         )
         birdseye_config_subscriber = ConfigSubscriber("config/birdseye", exact=True)
@@ -208,6 +209,10 @@ class OutputProcess(FrigateProcess):
                             birdseye,
                         )
 
+            if CameraConfigUpdateEnum.remove in updates:
+                for camera in updates["remove"]:
+                    frame_manager.close_camera(camera)
+
             _result = detection_subscriber.check_for_update(timeout=1)
             if _result is None:
                 continue
@@ -241,7 +246,7 @@ class OutputProcess(FrigateProcess):
                 continue
 
             frame = frame_manager.get(
-                frame_name, self.config.cameras[camera].frame_shape_yuv
+                frame_name, self.config.cameras[camera].frame_shape_yuv, frame_time
             )
 
             if frame is None:
@@ -296,8 +301,6 @@ class OutputProcess(FrigateProcess):
                     frame,
                 )
 
-            frame_manager.close(frame_name)
-
         move_preview_frames("clips")
 
         while True:
@@ -309,21 +312,6 @@ class OutputProcess(FrigateProcess):
             if not topic or data is None:
                 break
 
-            (
-                camera,
-                frame_name,
-                frame_time,
-                current_tracked_objects,
-                motion_boxes,
-                regions,
-            ) = data
-
-            camera_config = self.config.cameras.get(camera)
-
-            if camera_config is not None:
-                frame_manager.get(frame_name, camera_config.frame_shape_yuv)
-                frame_manager.close(frame_name)
-
         detection_subscriber.stop()
 
         for jsmpeg in jsmpeg_cameras.values():