Move more things out of FrigateApp (#13897)

* Moved FrigateApp.init_config() into FrigateConfig.load()

* Move frigate config loading into main

* Store PlusApi in FrigateConfig

* Register SIGTERM handler in main

* Ensure logging is setup during config parsing

* Removed pointless try

* Moved config initialization out of FrigateApp

* Made FrigateApp.shm_frame_count into a function

* Removed log calls from signal handlers

python's logging calls are not re-entrant, which caused at least one of
these to deadlock randomly.

* Reopen stdout/err on process fork

This helps avoid deadlocks (https://github.com/python/cpython/issues/91776).

* Make mypy happy

* Whoops. I might have forgotten to save.

Truly an amateur mistake.

* Always call FrigateApp.stop()

frigate/log.py

@@ -2,6 +2,7 @@ import atexit
 import logging
 import multiprocessing as mp
 import os
+import sys
 import threading
 from collections import deque
 from contextlib import AbstractContextManager, ContextDecorator
@@ -68,6 +69,19 @@ class log_thread(AbstractContextManager, ContextDecorator):
         self._stop_thread()
 
 
+# When a multiprocessing.Process exits, python tries to flush stdout and stderr. However, if the
+# process is created after a thread (for example a logging thread) is created and the process fork
+# happens while an internal lock is held, the stdout/err flush can cause a deadlock.
+#
+# https://github.com/python/cpython/issues/91776
+def reopen_std_streams() -> None:
+    sys.stdout = os.fdopen(1, "w")
+    sys.stderr = os.fdopen(2, "w")
+
+
+os.register_at_fork(after_in_child=reopen_std_streams)
+
+
 # based on https://codereview.stackexchange.com/a/17959
 class LogPipe(threading.Thread):
     def __init__(self, log_name: str):