micd: fix thread safety by adding locking for shared state (#35148)

* fix thread safety by adding locking for shared state

* Update system/micd.py

---------

Co-authored-by: Cameron Clough <cameronjclough@gmail.com>

system/micd.py

@@ -1,6 +1,7 @@
 #!/usr/bin/env python3
 import numpy as np
 from functools import cache
+import threading
 
 from cereal import messaging
 from openpilot.common.realtime import Ratekeeper
@@ -52,12 +53,18 @@ class Mic:
     self.sound_pressure_weighted = 0
     self.sound_pressure_level_weighted = 0
 
+    self.lock = threading.Lock()
+
   def update(self):
-    msg = messaging.new_message('microphone', valid=True)
-    msg.microphone.soundPressure = float(self.sound_pressure)
-    msg.microphone.soundPressureWeighted = float(self.sound_pressure_weighted)
+    with self.lock:
+      sound_pressure = self.sound_pressure
+      sound_pressure_weighted = self.sound_pressure_weighted
+      sound_pressure_level_weighted = self.sound_pressure_level_weighted
 
-    msg.microphone.soundPressureWeightedDb = float(self.sound_pressure_level_weighted)
+    msg = messaging.new_message('microphone', valid=True)
+    msg.microphone.soundPressure = float(sound_pressure)
+    msg.microphone.soundPressureWeighted = float(sound_pressure_weighted)
+    msg.microphone.soundPressureWeightedDb = float(sound_pressure_level_weighted)
 
     self.pm.send('microphone', msg)
     self.rk.keep_time()
@@ -69,7 +76,7 @@ class Mic:
 
     Logged A-weighted equivalents are rough approximations of the human-perceived loudness.
     """
-
+    with self.lock:
       self.measurements = np.concatenate((self.measurements, indata[:, 0]))
 
       while self.measurements.size >= FFT_SAMPLES: