RE: Passing lisp vector to foreign code

get_bytes is allocated by C from memory that is stable until the next call,
so that part is ok.

dey

-----Original Message-----
From: Martin Simmons [mailto:martin@lispworks.com]
Sent: Thursday, July 28, 2005 4:08 PM
To: deyoung@bloodhoundinc.com
Cc: lisp-hug@lispworks.com
Subject: Re: Passing lisp vector to foreign code


>>>>> On Thu, 28 Jul 2005 13:15:16 -0400, "Young, David"
<deyoung@bloodhoundinc.com> said:

  dey> Thanks. Here's how I got it working:

  dey> Outbound:

  dey> (let ((buf (output-buffer self))
  dey>       (bufsiz (buffer-size self)))
  dey>   (fli:with-dynamic-foreign-objects ()
  dey>     (let ((vector (fli:allocate-dynamic-foreign-object :type
`(:c-array
  dey> (:unsigned :char) ,bufsiz))))
  dey>       (dotimes (i bufsiz)
  dey>         (setf (fli:foreign-aref vector i) (aref buf i)))
  dey>       (put-bytes db vector bufsiz)

  dey> Inbound:

  dey> with-slots ((buf buffer)
  dey>              (len bufsiz)) self
  dey>   (multiple-value-bind (bytes nbytes)
  dey>       (get-bytes db)
  dey>     (let ((contents (loop for i from 0 below nbytes collect
(fli:dereference
  dey> bytes :index i))))
  dey>       (setf buf (make-array nbytes :initial-contents contents))
  dey>       (setf len (length buf)))))

  dey> Look reasonable?

What allocates the memory returned by get-bytes and should something free
it?

-- 
Martin Simmons                              Email: martin@lispworks.com
LispWorks Ltd, St John's Innovation Centre    TEL:   +44 1223 421860
Cowley Road, Cambridge CB4 0WS, England.      FAX:   +44 870 2206189



  dey> -----Original Message-----
  dey> From: Martin Simmons [mailto:martin@lispworks.com]
  dey> Sent: Thursday, July 28, 2005 1:10 PM
  dey> To: deyoung@bloodhoundinc.com
  dey> Cc: lisp-hug@lispworks.com
  dey> Subject: Re: Passing lisp vector to foreign code


>>>>> On Wed, 27 Jul 2005 11:26:44 -0400, "Young, David"
  dey> <deyoung@bloodhoundinc.com> said:

  dey> So, I have a binary stream class that collects bytes into a buffer
  dey> represented by a vector with a fill pointer. I want to take this
  dey> buffer and
  dey> send it to a C function, which stores it in a "database". Later, I
  dey> want to
  dey> retrieve this data via another binary stream class (we're
  dey> experimenting with
  dey> CL-STORE). Using the lw ffi, how do I set this up? It seems from the
  dey> docs
  dey> that I need to make a copy of the buffer in static space prior to
  dey> sending it
  dey> to C; is that correct? What should the ffi function declarations look
  dey> like?
  dey> Currently, I have:

  dey> (fli:define-foreign-function
  dey> (put-bytes "put_bytes" :source)
  dey> ((bytes (:c-array (:unsigned :char)))
  dey> (len :int))
  dey> :result-type :void
  dey> :calling-convention :cdecl)

  dey> (fli:define-foreign-function
  dey> (get-bytes "get_bytes" :source)
  dey> ((nbytes (:pointer (:int))))
  dey> :result-type (:c-array (:unsigned :char))
  dey> :calling-convention :cdecl)

  dey> But, passing a Lisp vector to PUT-BYTES yields a type error:

  dey> Expecting type (:foreign-array (:UNSIGNED :CHAR) (0)) (got #(76
  dey> ...))

  dey> so clearly I'm doing something wrong. Thanks for the help.

  dey> There are two kinds of static array: Lisp and foreign.  The :C-ARRAY
foreign
  dey> type needs a foreign array object (e.g. created with
  dey> FLI:ALLOCATE-FOREIGN-OBJECT).  See also the :LISP-ARRAY foreign type
if you
  dey> want to pass a static Lisp array pointer directly to C.

  dey> -- 
  dey> Martin Simmons                              Email:
martin@lispworks.com
  dey> LispWorks Ltd, St John's Innovation Centre    TEL:   +44 1223 421860
  dey> Cowley Road, Cambridge CB4 0WS, England.      FAX:   +44 870 2206189

This email message is for the sole use of the intended recipients(s) and may contain confidential and privileged information of Bloodhound Software, Inc.. Any unauthorized review, use, disclosure is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message.