Hi Philip, I think I'd have to see more code to really tell what the problem is, but here are some thoughts:
- A continuation captures the values of parameters at the time it is captured. So, if your parameterize is outside of the dispatcher that calls the continuation, then the code inside the continuation will not see the parameter change. That's a pretty important feature of continuations. - Web parameters would work the same way as normal parameters and not help you. - The stateless Web language guarantees that the parameters will have values they had when the servlet was initialized. - I think that you may want to use a thread-cell as the storage place. Jay On Thu, Jun 22, 2017 at 3:56 AM, Philip McGrath <phi...@philipmcgrath.com> wrote: > I'm encountering some strange behavior when using parameters with my > (stateless) web servlets. > > I want to check the value of a cookie every time a request is made to my > server and make a Racket value derived from the cookie's value available for > use within the servlet code. Since this value shouldn't be stored in the > continuation — it should be generated fresh for every request — it seemed > like writing a dispatcher (in the sense of serve/launch/wait, not of > dispatch-rules) was the right place to do this. Since the servlet code > itself does not need to (and indeed should not) modify the value, I thought > I could use a standard parameter to store the value. Essentially I have a > function shaped like this: > > (define ((wrap-dispatcher inner) connection request) > (parameterize ([my-param ...]) > (inner connection request))) > > where inner is a dispatcher produced by dispatch/servlet. > > All of the work being done by wrap-dispatcher seems to be happening > correctly (e.g. setting and reading the cookie), but within the servlet > itself, the parameter seems to get "stuck" on the first value installed by > wrap-dispatcher after the server is launched (which is not the default value > for the parameter). > > I'm not sure why this is happening. I understand that plain parameters > cannot be set within stateless servlets for serialization reasons (hence the > existence of web-parameters), but I didn't think that impacted code that > merely accesses the value of a parameter. > > More urgently, I'm not sure how to fix it. Would making my-param a web > parameter solve the problem (without storing the value in the continuation)? > Or is there some other method that should be used for this sort of > per-request work? > > Thanks, > Philip > > -- > You received this message because you are subscribed to the Google Groups > "Racket Users" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to racket-users+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- -=[ Jay McCarthy http://jeapostrophe.github.io ]=- -=[ Associate Professor PLT @ CS @ UMass Lowell ]=- -=[ Moses 1:33: And worlds without number have I created; ]=- -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
