Simulator: only send camera frames at rate that they are generated (#30802)

only send frames at rate that they are generated
old-commit-hash: 8017c25f0b2960db13df22295c077fbbd6aa6a07

tools/sim/lib/common.py

@@ -1,5 +1,5 @@
 import math
-import threading
+import multiprocessing
 import numpy as np
 
 from abc import ABC, abstractmethod
@@ -65,7 +65,7 @@ class World(ABC):
   def __init__(self, dual_camera):
     self.dual_camera = dual_camera
 
-    self.image_lock = threading.Lock()
+    self.image_lock = multiprocessing.Semaphore(value=0)
     self.road_image = np.zeros((H, W, 3), dtype=np.uint8)
     self.wide_road_image = np.zeros((H, W, 3), dtype=np.uint8)