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()
@@ -69,17 +76,17 @@ 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]))
 
-    self.measurements = np.concatenate((self.measurements, indata[:, 0]))
-
-    while self.measurements.size >= FFT_SAMPLES:
-      measurements = self.measurements[:FFT_SAMPLES]
+      while self.measurements.size >= FFT_SAMPLES:
+        measurements = self.measurements[:FFT_SAMPLES]
 
-      self.sound_pressure, _ = calculate_spl(measurements)
-      measurements_weighted = apply_a_weighting(measurements)
-      self.sound_pressure_weighted, self.sound_pressure_level_weighted = calculate_spl(measurements_weighted)
+        self.sound_pressure, _ = calculate_spl(measurements)
+        measurements_weighted = apply_a_weighting(measurements)
+        self.sound_pressure_weighted, self.sound_pressure_level_weighted = calculate_spl(measurements_weighted)
 
-      self.measurements = self.measurements[FFT_SAMPLES:]
+        self.measurements = self.measurements[FFT_SAMPLES:]
 
   @retry(attempts=7, delay=3)
   def get_stream(self, sd):