Hackergotchi doesn't work with trac 0.11.6

[Jens Langner]

After trying to install the HackergotchiPlugin in a trac 0.11.6 installation I get the following error:

ProgrammingError: Cannot operate on a closed cursor.

After some investigation and help from #trac I found the following code in Hackergotchi to be responsible for the error. Here is a patch for it:

Index: hackergotchi/web_ui.py
===================================================================
--- hackergotchi/web_ui.py	(revision 7751)
+++ hackergotchi/web_ui.py	(working copy)
@@ -29,8 +29,6 @@
     def filter_stream(self, req, method, filename, stream, data):
         if req.path_info.startswith('/timeline'):
             closure_state = [0]
-            db = self.env.get_db_cnx()
-            cursor = db.cursor()
             cache = {}
             def f(stream):
                 # Update the closed value
@@ -43,6 +41,8 @@
                 if user_info is not None:
                     author, name, email = user_info
                 else:
+                    db = self.env.get_db_cnx()
+                    cursor = db.cursor()
                     user_info = self._get_info(author, cursor)
                     cache[author] = user_info
                     author, name, email = user_info

After applying that patch the error disappeared.

[osimons]

Also see ​trac:ticket:9077#comment:9

[osimons]

#6302 closed as duplicate.

[Ryan J Ollos]

I've been trying to understand this issue by studying various cases where it appears (and it appears quite frequently!). Is it possible that the db object could still be garbage collected with this patch? What about the following alternative patch?

0.11/hackergotchi/web_ui.py

@@ -29 +29 @@
     def filter_stream(self, req, method, filename, stream, data):
         if req.path_info.startswith('/timeline'):
             closure_state = [0]
-            db = self.env.get_db_cnx()
-            cursor = db.cursor()
             cache = {}
             def f(stream):
                 # Update the closed value
@@ -43 +41 @@
                 if user_info is not None:
                     author, name, email = user_info
                 else:
-                    user_info = self._get_info(author, cursor)
+                    db = self.env.get_db_cnx()
+                    user_info = self._get_info(author, db)
                     cache[author] = user_info
                     author, name, email = user_info
                 
@@ -75 +74 @@
         return []
     
     # Internal methods
-    def _get_info(self, author, cursor):
+    def _get_info(self, author, db):
+        cursor = db.cursor()
         if author == 'anonymous':
             # Don't even bother trying for "anonymous"
             return author, None, None

[wrobel@…]

The same problem with trac 0.12

[Ryan J Ollos]

(In [11248]) Fixes #6765: Attempt to fix "Cannot operate on a closed cursor." error by passing the db object rather than the cursor object to the subfunction. The assumption here is that the db object is going out of scope.

I wasn't able to reproduce the issue with Trac 0.11 in a development environment. Please report back if this fixes the issue for you.

[Steffen Hoffmann]

Replying to rjollos:

(In [11248]) Fixes #6765: Attempt to fix "Cannot operate on a closed cursor." error by passing the db object rather than the cursor object to the subfunction. The assumption here is that the db object is going out of scope.

Sure, very reasonable IMHO. I've been looking for this kind of issue too after I got bitten by such a similar issue. Cursors should never be passed to methods/functions - another thing for our upcoming best-practice documentation.