nmhive.py: Use per-request database connections.

On #notmuch, Austin Clements just said:

  Opening the database always gives you a consistent snapshot, so you
  won't see changes unless you close and reopen it.  However, opening
  in read-only mode is quite cheap.

so I'm going to drop my global connection in favor of per-request
connections.  This also allows me to cleanup after aborted atomic
transactions (when I implement the POST backend), because notmuch does
not currently expose Xapian::WritableDatabase::cancel_transaction.  It
also allows other readers to see the new data, since notmuch only
commits changes when the database connection is closed.  Finally,
David Bremner pointed out that holding the read/write lock for an
extended period of time is just bad form.

diff --git a/nmhive.py b/nmhive.py
index 2acde49ee400ee5339f5c86b8f7693783d843e3b..841bccf0d2132d42308fa7985a496b0f40250cb2 100755 (executable)
--- a/nmhive.py
+++ b/nmhive.py
@@ -16,16 +16,19 @@ app.config['CORS_HEADERS'] = 'Content-Type'
 flask_cors.CORS(app)
 
 TAG_PREFIX = os.getenv('NMBPREFIX', 'notmuch::')
-NOTMUCH = None
-_TAGS = {}
+NOTMUCH_PATH = None
 
 
 @app.route('/tags', methods=['GET'])
 def tags():
     tags = set()
-    for t in NOTMUCH.get_all_tags():
-        if t.startswith(TAG_PREFIX):
-            tags.add(t[len(TAG_PREFIX):])
+    database = notmuch.Database(path=NOTMUCH_PATH)
+    try:
+        for t in database.get_all_tags():
+            if t.startswith(TAG_PREFIX):
+                tags.add(t[len(TAG_PREFIX):])
+    finally:
+        database.close()
     return flask.Response(
         response=json.dumps(sorted(tags)),
         mimetype='application/json')
@@ -77,7 +80,4 @@ def gmane_message_id(group, article):
 
 
 if __name__ == '__main__':
-    NOTMUCH = notmuch.Database(
-        path=None,
-        mode=notmuch.Database.MODE.READ_WRITE)
     app.run(host='0.0.0.0')