On Mon, Oct 8, 2012 at 4:48 PM, Norman Gray <[email protected]> wrote: > > Jay, hello. > > On 8 Oct 2012, at 20:23, Jay McCarthy <[email protected]> wrote: > >> All the functions that start the Web server (such as serve) return a >> function that with close the server when called. > > Thanks for this, but is that dependent on the version of Racket? I did > vaguely recall something like this mechanism, but when I look at > <http://docs.racket-lang.org/web-server/run.html#(def._((lib._web-server/servlet-env..rkt)._serve/servlet))> > (which is pointing to the v5.3 docs, I think), serve/servlet appears to > return void, and the only other serve/* procedure in the index to that part > is serve/dispatch, which also returns void. > > Am I looking in the wrong place? > > I see this shutdown procedure in > <http://docs.racket-lang.org/more/index.html#(part._.Terminating_.Connections>, > but that's in the context of a tutorial example. >
I was talking about these functions: http://docs.racket-lang.org/web-server-internal/web-server.html But you can just do (thread () (serve/servlet ...))) and then kill that thread or its custodian and it will do the same thing as serve/servlet's /quit URL does. >> All that function does is start the server with a particular custodian >> and then kills that custodian when you call the function. Any >> resources that the server allocates would have their will executors >> run. (The custodian controls the resources... killing it will cause >> the will executor to run on the resources, unless the process is >> killed, in which case nothing is normally run.) > > That makes sense, but I'm afraid I'm not seeing how I'd put my own function > (which will close/tidyup a database connection) into the care of the > current-custodian. I'm guessing that there's a link between custodians and > will-executors, but the Custodians section (13.7) doesn't mention wills, and > the section on Wills and Executors (15.3) doesn't mention custodians. 13.7 > doesn't seem to say how one would add something to a custodian; and 15.3, > although it suggests I should have a thread waiting on will-execute, doesn't > seem to guarantee that a will procedure is ever definitely ready, for example > when a web-server-closer procedure is called to terminate a custodian. > > The only thing I can think of is the following. Immediately after opening > the database, I evaluate (db is the db connection): > > (thread (λ () > (let ((box (sync (make-custodian-box (current-custodian) > db)))) > (eprintf "Custodian box: ~s [~s]~%" box (custodian-box? > box)) > (sql:close (custodian-box-value box)) > (eprintf "CLOSED!~%")))) > > When I Ctrl-C the server, however, I see the "Web Server stopped." which > comes from serve/launch/wait and its handler for exn:break? (yes?), but no > messages from this thread, even though the custodian-box should become ready > when the there-current custodian (which is surely one of those managed by the > server's custodian) is shut down. > > I'm guessing that I'm missing something, and in particular that there's some > document I'm missing. I'd love to RTFM, but I can't find which FM I should > be R-ing. You could do... (define we (make-will-executor) (will-register we db sql:close) (define we-t (thread (lambda () (will-execute we)))) And when the db was unreachable (because its custodian/thread/etc was killed), then the db would be closed. I believe you would have to ensure that we-t is not within the control of the same custodian. >> I don't have any Web apps that are started by anything other than a >> shell, so I always just Ctrl-C to quit. > > That's my situation, too. The server is started from a shell, but it opens a > database connection (in fact using (planet "sqlite.rkt" ("jaymccarthy" > "sqlite.plt" 5 1)), for which many thanks!), and I feel sure I should be > carefully calling (close db) at some point. I haven't been doing so, so far, > and nothing's broken, but I don't write to the database very often so I guess > I've just got away with it up to now. > You should switch to using the built-in 'db' library if possible. Ryan has fixed some errors and is otherwise doing a better job maintaining. Regarding if you need to close it... I never close my databases :/ The worst that could happen is a TXN gets rolled back when you restart because it was happening as you were killing. If you are not worried about that... Ctrl-C away! Jay > Or am I overcomplicating this, somehow? (not for the first time, regrettably…) > > Thanks for any pointers. > > Best wishes, > > Norman > > > -- > Norman Gray : http://nxg.me.uk > SUPA School of Physics and Astronomy, University of Glasgow, UK > -- Jay McCarthy <[email protected]> Assistant Professor / Brigham Young University http://faculty.cs.byu.edu/~jay "The glory of God is Intelligence" - D&C 93 ____________________ Racket Users list: http://lists.racket-lang.org/users
