test: create thread on endpoint

src/app.py

@@ -7,10 +7,12 @@ import os
 app = Flask(__name__)
 PORT = int(os.environ.get("PORT", 5000))
 
+instantiated = False
+
 latest_frame = None
 lock = threading.Lock()
 measured_fps = 0
-show_fps = False
+show_fps = True
 
 def video_reader():
     global latest_frame, lock, measured_fps
@@ -57,6 +59,8 @@ def video_reader():
 
 def generate():
     while True:
+        if latest_frame is None:
+            continue
         with lock:
             encode_param = [int(cv2.IMWRITE_JPEG_QUALITY), 50]
             ret, jpeg = cv2.imencode(".jpg", latest_frame, encode_param)
@@ -67,6 +71,12 @@ def generate():
             
 @app.route("/")
 def video_feed():
+    global instantiated
+
+    if not instantiated:
+        instantiated = True
+        threading.Thread(target=video_reader, daemon=True).start()
+        
     return Response(stream_with_context(generate()), mimetype="multipart/x-mixed-replace; boundary=frame")
 
 @app.route("/toggle_fps")
@@ -76,6 +86,4 @@ def toggle_fps():
     return f"fps counter: {"on" if show_fps else "off"}", 200
 
 if __name__ == "__main__":
-    t = threading.Thread(target=video_reader, daemon=True)
-    t.start()
     app.run(host="0.0.0.0", port=PORT, threaded=True)