Hi Wayne, Your `in-memory-database` is a parameter. Parameters are thread-specific storage [1]. Every request in the web-server is handled by a different thread, so I think this will not work how you think it should.
Jay 1. https://docs.racket-lang.org/reference/parameters.html#%28form._%28%28lib._racket%2Fprivate%2Fmore-scheme..rkt%29._parameterize%29%29 -- Jay McCarthy Associate Professor @ CS @ UMass Lowell http://jeapostrophe.github.io Vincit qui se vincit. On Tue, Aug 13, 2019 at 11:47 AM 'Wayne Harris' via Racket Users <racket-users@googlegroups.com> wrote: > > I'd like to save database results in memory because my database only changes > between long time intervals. By building a minimum application, I see my > cache-strategy seems to work per servlet: by opening a new browser, the first > request yields a cache-miss. > > Looking through the documentation, I got the idea that perhaps I should > serve/servlet using > > #:servlet-namespace '("shared-model.rkt") > > where shared-model.rkt is the module that talks to the database and > implements the caching-strategy. But adding this keyword to serve/servlet > did not make any perceived difference. > > What should I do to save results in memory across all requests? > > --- server.rkt > -------------------------------------------------------------------------- > #lang racket/base > (require > web-server/servlet > web-server/servlet-env > (prefix-in model: "shared-model.rkt")) > > (define-values (dispatch url) > (dispatch-rules > (("main") db->response) > (("update" (string-arg)) update->response))) > > (define (update->response r s) > (define str (model:in-memory-db-set-and-get s)) > (displayln str) > (string->response str)) > > (define (db->response r) > (string->response (model:get-in-memory-results))) > ;; no more api endpoints ==/== > > (define (string->response s) > (response/full 200 #"Okay" (current-seconds) > TEXT/HTML-MIME-TYPE '() (list (string->bytes/utf-8 s)))) > > (define (file-not-found r) > (response/xexpr "File not found.")) > > (module+ main > (file-stream-buffer-mode (current-output-port) 'line) > (define (main) > (displayln "Now serving...") > (serve/servlet dispatch > ;; #:servlet-namespace '("shared-model.rkt") > #:stateless? #t > #:log-file (build-path "logs/httpd.log") > #:port 1111 > #:listen-ip "127.0.0.1" > #:servlet-path "/" > #:servlet-regexp #rx"" > #:extra-files-paths (list (build-path "pub/")) > #:server-root-path (build-path "/") > #:file-not-found-responder file-not-found)) > (main)) > --------------------------------------------------------------------------- > > --- shared-model.rkt > --------------------------------------------------------------------------- > #lang racket/base > (define in-memory-database (make-parameter #f)) > (define (in-memory-db-set-and-get x) > (in-memory-database (format "~a: data to be shared across servlets" x)) > (in-memory-database)) > > (define (get-in-memory-results [refresh? #f]) > (if refresh? > (begin (displayln "database: force refresh") > (in-memory-db-set-and-get "forced")) > (let ([in-memory-db (in-memory-database)]) > (if in-memory-db > (begin (displayln "database: cache hit") > in-memory-db) > (begin (displayln "database: cache miss") > (in-memory-db-set-and-get "miss")))))) > (provide (all-defined-out)) > --------------------------------------------------------------------------- > > -- > 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. > To view this discussion on the web visit > https://groups.google.com/d/msgid/racket-users/Xuxg1t5egDEkFLVsH-Ch9KZyTqtLjhATNOPD-HeXZgcOc2mXr8qlXS3fZTZRh90xd2kvhdILhNjKwUllUirBcnTrEzPDTiw_hJDVEp5FjpM%3D%40protonmail.com. -- 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. To view this discussion on the web visit https://groups.google.com/d/msgid/racket-users/CAJYbDa%3DfCWDuk_MdOUokhF4sOaLe3_fGq24SJDRSDFCG%3DFRsZA%40mail.gmail.com.
