From a6587b1f3ddd3e509a9098c13e7707712dab34c4 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sat, 19 Sep 2020 06:46:01 +0530
Subject: [PATCH] oops forgot to protect set_namespaced()

---
 src/calibre/db/legacy.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/calibre/db/legacy.py b/src/calibre/db/legacy.py
index 359d368ab6..baec62e603 100644
--- a/src/calibre/db/legacy.py
+++ b/src/calibre/db/legacy.py
@@ -136,8 +136,10 @@ class ThreadSafePrefs(MutableMapping):
         return prefs.get_namespaced(namespace, key, default)
 
     def set_namespaced(self, namespace, key, val):
-        prefs = self.db().backend.prefs
-        return prefs.set_namespaced(namespace, key, val)
+        db = self.db()
+        with db.write_lock:
+            prefs = db.backend.prefs
+            return prefs.set_namespaced(namespace, key, val)
 
 
 class LibraryDatabase(object):