When I say "code", I mean module top-level binding byte-code. There's no way for Racket to remove
(define (f x) (lambda (y) (printf "Gigantic string: ~a" (+ x y)))) at the top-level. The byte-code will always contain the gigantic string. If you ever call f and get back something, that closure could be collected, but not the source that generated it. Jay On Thu, Feb 14, 2013 at 6:37 AM, Robby Findler <ro...@eecs.northwestern.edu> wrote: > I'm pretty sure code is collected in (regular) Racket. Small numbers aren't > collected, true, but they also don't really take any space. Big numbers are > collected, too. (I'm not sure about interned symbols.) > > Robby > > > On Thu, Feb 14, 2013 at 7:26 AM, Jay McCarthy <jay.mccar...@gmail.com> > wrote: >> >> In the Web server language, all anonymous functions are turned into >> top-level structures masquerading as functions where the fields are >> their free variables. For instance: >> >> (define (f x) (lambda (y) (+ x y)) >> >> becomes, roughly, >> >> (struct a-lambda42 (x) >> #:property prop:procedure >> (lambda (the-structure y) >> (define x (a-lambda42-x the-structure)) >> (+ x y))) >> (define (f x) (make-a-lambda42 x)) >> >> In your program, the expression >> >> (web-cell-shadow wc-anonymous (λ (x) 'more-distinctive-text)) >> >> becomes >> >> (struct a-lambda43 () #:property prop:procedure (lambda (s x) >> 'more-distinctive-text)) >> (web-cell-shadow wc-anonymous (make-a-lambda43)) >> >> Notice that the anonymous function has no fields because there are no >> free variables. The distinctive text is not shown anywhere in the URL >> because it is part of the code, not part of the data, of the closure. >> >> If you change the program slightly to >> >> (web-cell-shadow wc-anonymous >> (let () (define y 'more-distinctive-text) >> (λ (x) y))) >> >> then y is a free variable, so when you look at the URL: >> >> >> http://localhost:8000/;((%22c%22%20.%20%220((3)%204%20(((lib%20%5C%22web-server%2Flang%2Fabort-resume.rkt%5C%22)%20.%20%5C%22lifted.6%5C%22)%20((lib%20%5C%22web-server%2Flang%2Fweb-cells.rkt%5C%22)%20.%20deserialize-info:frame-v0)%20(%23%5C%22%2Ftmp%2Ft.rkt%5C%22%20.%20%5C%22lifted.1683%5C%22)%20(2%20.%20%5C%22lifted.1991%5C%22))%200%20()%20()%20(0%20(1%20(h%20-%20()%20(lifted.1485-0%20.%20this-is-a-song-about-Japan)%20(lifted.1521-1%202%20(b!%20.%20more-distinctive-text))))%20(c%20(v!%20(3)%20%23f%20%23f))))%22)) >> >> You see the distinctive text. >> >> As far as GC goes, code is not generally collected in Racket anyways. >> Any data that is an intrinsic part of the program text (such as >> literal symbols and numbers) will always be around in your program >> whether you use #lang web-server or not. >> >> Jay >> >> >> On Wed, Feb 13, 2013 at 8:34 PM, Galler <lzgal...@optonline.net> wrote: >> > Good evening, >> > >> > I've been investigating lang web-server, performance and garbage >> > collection >> > >> > I have a question regarding anonymous functions and web cells >> > >> > Examples below require: >> > >> > #lang web-server >> > (require racket/serialize >> > web-server/lang/web-cells) >> > >> > >> > Constants appear serializable by their value being explicitly written >> > out >> > >> > >> > For example, >> > >> > (serialize 'this-is-a-song-about-japan) >> > >> > ;-> '((3) 0 () 0 () () this-is-a-song-about-japan) >> > >> > >> > Whereas anonymous functions appear serializable by the mechanism of >> > being >> > "lifted" (i.e. reified) to a module level binding >> > >> > For example >> > >> > (serialize (λ (x) x)) >> > >> > ;-> '((3) 1 (('anonymous-module . "lifted.1386")) 0 () () (0)) >> > >> > >> > Moving the discussion to web-cells >> > >> > (define wc-constant (make-web-cell #f)) >> > >> > (define wc-anonymous (make-web-cell #f)) >> > >> > >> > (web-cell-shadow wc-constant 'this-is-a-song-about-Japan) >> > >> > (web-cell-shadow wc-anonymous (λ (x) x)) >> > >> > (printf " wc-constant: ~A\n wc-anonymous: ~A\n" >> > (serialize wc-1) >> > (serialize wc-2)) >> > >> > returns >> > >> > wc-constant: ((3) 1 (((lib web-server/lang/web-cells.rkt) . >> > deserialize-info:primitive-wc-v0)) 0 () () (0 lifted.1534-0)) >> > >> > wc-anonymous: ((3) 1 (((lib web-server/lang/web-cells.rkt) . >> > deserialize-info:primitive-wc-v0)) 0 () () (0 lifted.1570-1)) >> > >> > >> > >> > While now both values are 'lifted' (i.e. reified), a close examination >> > of >> > the URL-string sent back to a client after send/suspend/dispatch >> > >> > reveals that, with respect to the constant, lifted.1534 appears to be >> > explicitly represented, elsewhere in the string as an associative pair >> > i.e. >> > (lifted.1534 this-is-a-song-about-Japan) >> > >> > whereas for the anonymous function, its not clear that its reference, >> > lifted.1570 is explicitly represented >> > >> > Which leads me to wonder about whether the reference to the anonymous >> > function, lifted.1570, is being maintained on the server, >> > >> > And if so, how is it being garbage collected, as its impossible to ever >> > determine that it is unreachable. >> > >> > I will also point out that prior to a year ago, anonymous functions >> > failed >> > the serializability predicate. (serializable? anon-func) -> #f. I can >> > pull >> > out the correspondence/background related to that if desirable. >> > >> > I apologize if I'm just misreading the data. >> > >> > Here's the complete example,with a stateless web server. Note that when >> > you >> > inspect the url-string**for the datum this-is-a-song-about-Japan, its >> > there, >> > but when looking for the datum more-distinctive-text, its not present in >> > the >> > url-string. >> > >> > **right click on the link, then copy/paste, or click the 'click-me' link >> > and >> > copy/paste the URL from the address bar) >> > >> > Thanks very much. >> > >> > >> > Thanks again. >> > >> > >> > >> > #lang web-server >> > >> > (require web-server/servlet-env) >> > >> > (define wc-constant (make-web-cell #f)) >> > >> > (define wc-anonymous (make-web-cell #f)) >> > >> > >> > (web-cell-shadow wc-constant 'this-is-a-song-about-Japan) >> > >> > (web-cell-shadow wc-anonymous (λ (x) 'more-distinctive-text)) >> > >> > (define (start request) >> > (letrec ((response-generator (λ (make-url) >> > (response/xexpr `(html (head) >> > (body (a ((href >> > ,(format "~A" (make-url receive-request)))) "click me")))))) >> > (receive-request (λ (request) >> > (response/xexpr `(html (head) >> > (body "Thank you. >> > We >> > are done.")))))) >> > (send/suspend/dispatch response-generator))) >> > >> > (serve/servlet start >> > #:stateless? #t >> > #:launch-browser? #t >> > #:connection-close? #t >> > #:quit? #f >> > #:listen-ip #f >> > #:port 8000 >> > #:servlet-path "/") >> > >> > >> > >> > Thanks much. >> > >> > Zack >> >> >> >> -- >> Jay McCarthy <j...@cs.byu.edu> >> 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 > > -- Jay McCarthy <j...@cs.byu.edu> 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
