+ ;; FIXME: GC safety alert! These SAPs are not safe, since the
+ ;; Lisp string can move. This is not hard to arrange, for example
+ ;; the following will fail very quickly on a SB-UNICODE build:
+ ;;
+ ;; (setf (bytes-consed-between-gcs) 4096)
+ ;; (define-alien-routine "strcmp" int (s1 c-string) (s2 c-string))
+ ;;
+ ;; (loop
+ ;; (let ((string "hello, world"))
+ ;; (assert (zerop (strcmp string string)))))
+ ;;
+ ;; (This will appear to work on post-0.9.8.19 GENCGC, since
+ ;; the GC no longer zeroes memory immediately after releasing
+ ;; it after a minor GC. Either enabling the READ_PROTECT_FREE_PAGES
+ ;; #define in gencgc.c or modifying the example so that a major
+ ;; GC will occasionally be triggered would unmask the bug).
+ ;;
+ ;; The pure VECTOR-SAP branch for the SIMPLE-BASE-STRING case
+ ;; will generally be very hard to trigger on GENCGC (even when
+ ;; threaded) thanks to GC conservativeness. It's mostly a problem
+ ;; on cheneygc. -- JES, 2006-01-13
+ (simple-base-string
+ ,(if (c-string-needs-conversion-p type)
+ ;; If the alien type is not ascii-compatible (+SB-UNICODE)
+ ;; or latin-1-compatible (-SB-UNICODE), we need to do
+ ;; external format conversion.
+ `(vector-sap (string-to-c-string ,value
+ (c-string-external-format ,type)))
+ ;; Otherwise we can just pass it uncopied.
+ `(vector-sap ,value)))
+ ;; This case, on the other hand, will cause trouble on GENCGC, since
+ ;; we're taking the SAP of a immediately discarded temporary -> the
+ ;; conservativeness doesn't protect us.
+ ;; -- JES, 2006-01-13
+ (simple-string
+ (vector-sap (string-to-c-string ,value
+ (c-string-external-format ,type))))))