Racket will generally not release keys that are quoted literals in your program. Try building your keys using symbol->string. On Jan 28, 2014 8:16 AM, "Jos Koot" <[email protected]> wrote:
> Things work now as I expect for weak boxes, but I am still confused > about weak hash tables. I do the following: > > #lang racket > > (define h (make-weak-hash)) > > (define keys > (for/list ((key (in-list '(a b c d e f)))) > (make-weak-box key) ; <--- 1 > ; key ; <--- 2 > )) > > (define (enter key value) > (will-register will-executor value will-proc) > (set! enter-counter (add1 enter-counter)) > (hash-set! h key value)) > > (define-syntax-rule (while condition expr ...) > (let loop () (when condition expr ... (loop)))) > > (define will-executor (make-will-executor)) > (define (will-proc v) (set! release-counter (add1 release-counter)) #t) > (define enter-counter 0) > (define release-counter 0) > (define range (in-range 6)) > (for ((key (in-list keys)) (value range)) (enter key (list value))) > (list enter-counter release-counter) ; -> (6 0) ok > h ; -> hash with 6 entries, ok > (set! keys #f) ; discard all keys > (collect-garbage) (collect-garbage)(collect-garbage) (collect-garbage) > (while (will-try-execute will-executor)) > (list enter-counter release-counter) ; -> (6 6) ok > h ; -> empty hash, ok > > So far ok. However, when commenting out line <--- 1 and uncommenting line > <--- 2, I would expect the same results, but I find: > > (6 0) ; ok > hash with 6 entries ; ok > (6 0) ; a surptrise for me > hash with 6 entries ; a surprise for me > > This is the cause of my confusion. Surely I am misinterpreting the docs. > Help much appreciated. > > Thanks again, Jos > > > > > ------------------------------ > *From:* Carl Eastlund [mailto:[email protected]] > *Sent:* martes, 28 de enero de 2014 1:28 > *To:* Jos Koot > *Cc:* Racket Users > *Subject:* Re: [racket] FW: weakly held symbols? > > This isn't a typo. The docs are talking about the properties of the > symbol tables for interned and unreadable symbols. There is no symbol > table for uninterned symbols, so it wouldn't mean anything to talk about it. > > Here's what this means for an interned symbol: you can create one, and > while a reference to it exists, it stays in the symbol table. Any time you > intern the same string, you'll get back that symbol. However, if all > references to that symbol vanish, the symbol table is free to release that > symbol. If anyone interns the same string again later, a new symbol will > be created. For nearly all purposes, this is completely transparent, > because you couldn't possibly have a copy of the old symbol to compare. > There's almost no way to tell that the symbol you got before and the one > you got after were different. The only way you'd ever know would be either > by tracking memory use statistics, or by comparing the results of something > like eq-hash-code, neither of which should be surprising to find out > behaves impurely. > > Carl Eastlund > > > On Mon, Jan 27, 2014 at 5:53 PM, Jos Koot <[email protected]> wrote: > >> It appears that my previous email was not sent completely. Sorry for >> that. Here is the complete question. >> >> Hi to all, >> >> Section "3.6 symbols" of the Racket reference manual states: >> >> Interned and unreadable symbols are only weakly held ... but a symbol >> maay disappear when ... used as the key in a weak hash table ...". >> >> I would understand: >> >> UNINTERNED and unreadable symbols are only weakly held ... but a symbol >> may disappear when ... used as the key in a weak hash table ...". >> >> May be just a typo, but as I am not sure I understand the docs well, I >> post my question here instead of posting a bug report. >> >> Greetings, Jos >> >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users >> >> >
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