[Web-SIG] Closing long-running WSGI requests (possible?)

[Chimezie Ogbuji]

Hello.  I have a problem with a WSGI-based SPARQL server that I have been
unable to resolve for some time.  I was told this is the best place to ask
:).  I'm building a SPARQL [1] server that is deployed as  WSGI/Paste
server.  SPARQL queries are handled by the server and evaluated against a
MySQL database using mysql-python/MySQLdb to manage the connection.

My goal is to be able to allow clients to close the connection in order to
kill queries that have been dispatched (in order to 'abort' them).
Unfortunately, when the client kills the connection, the application is not
signaled in any way.  So, the result is that (for long-running queries), the
MySQL query continues to run even after the connection is closed (by
clicking cancel in the browser for instance).

I would expect that when the connection is closed at the client side, this
should trigger a chain reaction of garbage collection (deletion of the
application object, and all the objects attributed to it including the DB
connection, etc.) that bottoms out in the db connection closing and MySQLdb
killing the query as a side effect of calling __del__ on the cursor and
database connection.  However, this is not what is happening and it appears
that the once the result is served back to the client, the server and the
client are completely 'disconnected' for that particular request.

Am I going about his the wrong way? Does WSGI simply not have anything to
say about such a situation ? If the problem isn't
WSGI, is there another WSGI implementation that is known to behave as
expected (i.e., closing the connection dispatches the deletion of the
objects involved in the request handling)?

I was told to look into keep-alive, but the specification doesn't seem to
suggest that this would help me as it has more to do with re-using
connections for subsequent requests rather than specifying that the server
maintains a connection between the request and the objects involved in
handling the request at the server.

Any help would be greatly appreciated.

Thanks

[1] http://www.w3.org/TR/rdf-sparql-query/


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