Reference-Counted Object Management with Dynamic Destructors

#include <stdio.h>
#include <stdlib.h>
 
typedef struct RefCounted RefCounted;
typedef void (*DestructorFunc)(void* self);
 
struct RefCounted {
    size_t ref_count;
    DestructorFunc dtor;
};
 
void ref_init(RefCounted* obj, DestructorFunc dtor) {
    obj->ref_count = 1;
    obj->dtor = dtor;
}
 
void ref_retain(RefCounted* obj) {
    if (obj) obj->ref_count++;
}
 
void ref_release(RefCounted* obj) {
    if (obj && --obj->ref_count == 0) {
        if (obj->dtor) obj->dtor(obj);
    }
}
 
typedef struct {
    RefCounted ref;
    int handle;
} Resource;
 
void resource_destroy(void* ptr) {
    Resource* res = (Resource*)ptr;
    printf("Closing resource handle %d\n", res->handle);
    free(res);
}
 
int main(void) {
    Resource* r = (Resource*)malloc(sizeof(Resource));
    ref_init(&r->ref, resource_destroy);
    r->handle = 42;
    ref_retain(&r->ref);
    ref_release(&r->ref);
    ref_release(&r->ref);
    return 0;
}