Add config file locking

basic/srv/vm/mgr/config.py

@@ -1,20 +1,27 @@
 # -*- coding: utf-8 -*-
 
+import fcntl
 import json
 
 CONF_FILE = '/srv/vm/config.json'
+# Locking is needed in order to prevent race conditions in WSGI threads
+LOCK_FILE = '/srv/vm/config.lock'
 
 class Config:
     def __init__(self):
         self.load()
 
     def load(self):
-        with open(CONF_FILE, 'r') as f:
-            self.data = json.load(f)
+        with open(LOCK_FILE, 'w') as l:
+            fcntl.flock(l, fcntl.LOCK_EX)
+            with open(CONF_FILE, 'r') as f:
+                self.data = json.load(f)
 
     def save(self):
-        with open(CONF_FILE, 'w') as f:
-            json.dump(self.data, f, sort_keys=True, indent=4)
+        with open(LOCK_FILE, 'w') as l:
+            fcntl.flock(l, fcntl.LOCK_EX)
+            with open(CONF_FILE, 'w') as f:
+                json.dump(self.data, f, sort_keys=True, indent=4)
 
     def __getitem__(self, attr):
         return self.data[attr]