countup closure in C

closure-counter.c

// gcc -o closure-counter closure-counter.c -lffi
#include <stddef.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <ffi.h>

int
main(int argc, char **argv) {
    ffi_cif cif;
    typedef struct { int count; } count_info_t;
    typedef int (*countup_func_t)();
    void countup_func(ffi_cif *cif, void *ret, void **args, void *user_data) {
        count_info_t* ci = (count_info_t*) user_data;
        *(int*)ret = ++ci->count;
    };
    typedef struct _countup_closure_t {
        ffi_closure clos;
        ffi_cif cif;
        countup_func_t countup;
    } countup_closure_t;
    countup_closure_t* create_counter(int count) {
        void *codeloc;
        count_info_t* ci;
        countup_closure_t* cct;
        cct = (countup_closure_t*) ffi_closure_alloc(sizeof(countup_closure_t)+sizeof(int), &codeloc);
        if (!cct) return NULL;
        cct->countup = codeloc;
        cct->cif = cif;
        ci = (count_info_t*) malloc(sizeof(count_info_t));
        ci->count = (int) count;
        ffi_prep_closure_loc(&cct->clos, &cct->cif, countup_func, (void*)ci, codeloc);
        return cct;
    }
    void destroy_counter(countup_closure_t *cct) {
        free(cct->clos.user_data);
        ffi_closure_free(cct);
    }
    countup_closure_t* counter1;
    countup_closure_t* counter2;
    countup_closure_t* counter3;

    // initialize
    ffi_prep_cif(&cif, FFI_DEFAULT_ABI, 0, &ffi_type_sint, NULL);

    // create closure
    counter1 = create_counter(1);
    counter2 = create_counter(3);
    counter3 = create_counter(5);

    // invoke...
    printf("counter1() = %d\n", counter1->countup()); // 2
    printf("counter2() = %d\n", counter2->countup()); // 4
    printf("counter3() = %d\n", counter3->countup()); // 6
    printf("counter1() = %d\n", counter1->countup()); // 3
    printf("counter2() = %d\n", counter2->countup()); // 5
    printf("counter3() = %d\n", counter3->countup()); // 7

    // destroy counter
    destroy_counter(counter1);
    destroy_counter(counter2);
    destroy_counter(counter3);

    return 0;
}