db/manager: use only one worker thread for write operations

There is no point in having more, as the database cannot have more than
one writer at any moment.

1 files changed, 11 insertions, 8 deletions

diff --git a/alot/db/manager.py b/alot/db/manager.py
index aa67ed40..56f71bd1 100644
--- a/alot/db/manager.py
+++ b/alot/db/manager.py
@@ -4,6 +4,7 @@
 
 import abc
 import asyncio
+from   concurrent.futures import ThreadPoolExecutor
 from   contextlib import closing
 from   functools  import partialmethod
 import logging
@@ -232,16 +233,18 @@ class DBManager:
     async def _db_write_task(self):
         # this task serialises write operations on the database and
         # sends them off to a thread so they do not block the event loop
-        while True:
-            cur_item = await self._write_queue.get()
-            if cur_item is None:
-                self._write_queue.task_done()
-                break
+        # one workers, as there can be only one DB writer at any moment
+        with ThreadPoolExecutor(max_workers = 1) as executor:
+            while True:
+                cur_item = await self._write_queue.get()
+                if cur_item is None:
+                    self._write_queue.task_done()
+                    break
 
-            logging.debug('submitting write task: %s', cur_item)
+                logging.debug('submitting write task: %s', cur_item)
 
-            await self._loop.run_in_executor(None, cur_item.apply)
-            self._write_queue.task_done()
+                await self._loop.run_in_executor(executor, cur_item.apply)
+                self._write_queue.task_done()
 
     def tags_add(self, query, tags):
         """