Fixed database file race condition

torch_sub/torch_sub.py

@@ -1,20 +1,23 @@
 import json
 import os
+import threading
 
 import paho.mqtt.subscribe as mqtt
 
 database_file = "clients.json"
-
+database_lock = threading.Lock()
 
 # noinspection PyUnusedLocal
 def update_client_record(client, userdata, message):
 
+    database_lock.acquire()
+
     if not os.path.exists(database_file):
         with open(database_file, 'w') as database_blank:
-            database_blank.write("{}")
+            json.dump({}, database_blank)
 
     with open(database_file, 'r') as infile:
-        database = json.loads(infile.read())
+        database = json.load(infile)
 
     payload = message.payload.decode('utf-8')
     response = json.loads(payload)
@@ -24,6 +27,8 @@ def update_client_record(client, userdata, message):
     with open(database_file, 'w') as outfile:
         json.dump(database, outfile)
 
+    database_lock.release()
+
 
 def subscribe(broker_hostname, broker_port, topic="torch", tls=None, auth=None):
     mqtt.callback(update_client_record,