How to use FFI:def-call-in in clisp - lisp

Question

I have figured out how to make use of shared objects created from C code into Clisp using FFI:def-call-out but I am not able to figure out how to use FFI:Def-call-in.
I don't know the process and actually I am confused if clisp will also create some .so file that some C function can use or something else.
Can someone please explain a minimal working example for writing such callback functions ?

Answer 1

Example 32.7. Calling Lisp from C:
To sort an array of double-floats using the Lisp function SORT instead of the C library function qsort, one can use the following interface code sort1.c. The main problem is to pass a variable-sized array.
extern void lispsort_begin (int);
void* lispsort_function;
void lispsort_double (int n, double * array) {
double * sorted_array;
int i;
lispsort_begin(n); /* store #'sort2 in lispsort_function */
sorted_array = ((double * (*) (double *)) lispsort_function) (array);
for (i = 0; i < n; i++) array[i] = sorted_array[i];
free(sorted_array);
}
This is accompanied by sort2.lisp:
(DEFPACKAGE "FFI-TEST" (:use “COMMON-LISP” “FFI”))
(IN-PACKAGE "FFI-TEST")
(EVAL-WHEN (compile) (setq FFI:*OUTPUT-C-FUNCTIONS* t))
(FFI:DEF-CALL-IN lispsort_begin (:ARGUMENTS (n int))
(:RETURN-TYPE nil)
(:LANGUAGE :stdc))
(FFI:DEF-C-VAR lispsort_function (:type c-pointer))
(defun lispsort_begin (n)
(setf (cast lispsort_function
`(c-function
(:ARGUMENTS (v (c-ptr (c-array double-float ,n))))
(:RETURN-TYPE (c-ptr (c-array double-float ,n))
:malloc-free)))
#'sort2))
(defun sort2 (v)
(declare (type vector v))
(sort v #'<))
To test this, use the following test file sorttest.lisp:
(EVAL-WHEN (compile) (setq FFI:*OUTPUT-C-FUNCTIONS* t))
(FFI:DEF-CALL-OUT sort10
(:name "lispsort_double")
(:LANGUAGE :stdc)
(:ARGUMENTS (n int)
(array (c-ptr (c-array double-float 10)) :in-out)))
Now try
$ clisp-link create sort sort2.c sorttest.c
$ cc -O -c sort1.c
$ cd sort
$ ln -s ../sort1.o sort1.o
Add sort1.o to NEW_LIBS and NEW_FILES in link.sh. Create a file package.lisp containing the form
(MAKE-PACKAGE "FFI-TEST" :use '(“COMMON-LISP” “FFI”))
and add package.lisp to TO_PRELOAD in link.sh. Proceed:
$ cd ..
$ base/lisp.run -M base/lispinit.mem -c sort2.lisp sorttest.lisp
$ clisp-link add base base+sort sort
$ base+sort/lisp.run -M base+sort/lispinit.mem -i sort2 sorttest
> (sort10 10 '#(0.501d0 0.528d0 0.615d0 0.550d0 0.711d0
0.523d0 0.585d0 0.670d0 0.271d0 0.063d0))
#(0.063d0 0.271d0 0.501d0 0.523d0 0.528d0 0.55d0 0.585d0 0.615d0 0.67d0 0.711d0)
$ rm -r base+sort