Add a lock to allow plugins to sync access to the Kobo db

src/calibre/devices/kobo/db.py

@@ -4,12 +4,17 @@
 import os
 import shutil
 from contextlib import closing, suppress
+from threading import RLock
 
 import apsw
 
 from calibre.prints import debug_print
 from calibre.ptempfile import PersistentTemporaryFile, TemporaryDirectory
 
+# Any plugins not running in the device thread must acquire this lock before
+# trying to access the Kobo database.
+kobo_db_lock = RLock()
+
 
 def row_factory(cursor: apsw.Cursor, row):
     return {k[0]: row[i] for i, k in enumerate(cursor.getdescription())}
@@ -68,14 +73,18 @@ class Database:
                 raise
 
     def __enter__(self) -> apsw.Connection:
+        kobo_db_lock.acquire()
         self.conn = apsw.Connection(self.dbpath)
         if self.use_row_factory:
             self.conn.setrowtrace(row_factory)
         return self.conn.__enter__()
 
     def __exit__(self, exc_type, exc_value, tb) -> bool | None:
+        try:
             with closing(self.conn):
                 suppress_exception = self.conn.__exit__(exc_type, exc_value, tb)
                 if self.needs_copy and (suppress_exception or (exc_type is None and exc_value is None and tb is None)):
                     copy_db(self.conn, self.path_on_device)
+        finally:
+            kobo_db_lock.release()
         return suppress_exception