This looks right as far as I can tell, except that you need to return `res` after the `memcpy`.
At Sun, 26 Jan 2014 00:08:09 +0400, Roman Klochkov wrote: > So, to make string, that is freed by reciever, I should make something like > > (define _string/transfer > (make-ctype _bytes > (λ (v) > (define b (if (string? v) (string->bytes/utf-8 v) > v)) > (define length (bytes-length b)) > (define res (malloc 'raw length)) > (memcpy res b length)) (λ > (v) > (register-finalizer v free)))) > > Or finalizer will not work (because v is _pointer, but the type returns > _bytes), and instead I have to make > (λ (v) > (define res (cast v _pointer _bytes)) > (register-finalizer v free)) > > ? > > > Суббота, 25 января 2014, 14:37 -05:00 от Ryan Culpepper <ry...@ccs.neu.edu>: > >On 01/25/2014 01:28 PM, Roman Klochkov wrote: > >> Is making bytestring from pointer adds the pointer to GC? > >> > >> > >> > (define x (malloc 'raw 10)) > >> > x > >> #<cpointer> > >> > (define b (make-sized-byte-string x 10)) > >> > (cpointer-gcable? b) > >> #t > >> > (cpointer-gcable? x) > >> #f > >> > (cast x _pointer _int32) > >> 173726656 > >> > (cast b _pointer _int32) > >> 173726656 > >> > >> So b and x points to the same block of 10 bytes, but value of b is > >> GCable and value of x is not. > >> I assume, that when b will be changed, then the bytestring will be > >> collected and accessing x will give segfault. Am I right? > > > >I think it's a bug that (cpointer-gcable? b) returns true, since the FFI > >generally treats bytestrings as pointers to the memory that stores their > >contents, and in this case that memory is not managed by the GC. > > > >The bytestring object itself (which consists of a header, a pointer, and > >a length, IIRC) is collectible, but then so is the cpointer object > >(which consists of a header, a pointer, and some other stuff, like a tag > >list). > > > >So no, you should not expect a segfault. On the other hand, if you free > >x and use b afterwards, then you should expect a segfault or some other > >form of memory corruption. > > > >Ryan > > > > > -- > Roman Klochkov > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
