Reference_Linking/rl.c

#include "rl.h"
#include <stdbool.h>
#include <malloc.h>

struct RlBox {
    bool marked;
    Rl* first;
    Rl* last;
    Destructor destructor;
};

#define RLBOX_SIZE sizeof(struct RlBox)
#define PTR_TO_RLBOX(ptr) ((struct RlBox*)((ptr) - RLBOX_SIZE))

inline void rl_alloc(Rl* reference, const void* owner, const size_t size, const Destructor destructor) {
    struct RlBox* box = (struct RlBox*) malloc(RLBOX_SIZE + size);
    box->marked = false;
    box->first = NULL;
    box->last = NULL;
    box->destructor = destructor;
    reference->prev = NULL;
    reference->next = NULL;
    reference->owner = PTR_TO_RLBOX(owner);
    reference->ref = box + RLBOX_SIZE;
}

// reference may not point to a valid object
inline void rl_set(Rl* reference, const void* owner, const Rl* copy) {
    reference->prev = PTR_TO_RLBOX(copy->ref)->last;
    reference->next = NULL;
    reference->owner = PTR_TO_RLBOX(owner);
    reference->ref = copy->ref;
    reference->prev->next = reference;
}

static void unmark(struct RlBox* obj) {
    if(!obj->marked)
        return;
    obj->marked = false;

    Rl* ref = obj->first;
    while(ref) {
        unmark(ref->owner);
        ref = ref->next;
    }
}

static bool search_root(struct RlBox* obj) {
    if(obj->marked)
        return false;
    obj->marked = true;

    Rl* ref = obj->first;
    while(ref) {
        if(!ref->owner || search_root(ref->owner)) {
            // mark reversal
            Rl* prev = ref->prev;
            while(prev) {
                unmark(prev->owner);
                prev = ref->prev;
            }
            obj->marked = false;

            // reordering
            if(ref != obj->first) {
                if(ref->next)
                    ref->next->prev = ref->prev;
                else
                    obj->last = ref->prev;
                ref->prev->next = ref->next;

                obj->first->prev = ref;
                obj->first = ref;
            }

            return true;
        }

        ref = ref->next;
    }

    return false;
}

inline void rl_free(Rl* reference) {
    struct RlBox* obj = PTR_TO_RLBOX(reference->ref);
    if(obj->first != reference) {
        if(reference->next)
            reference->next->prev = reference->prev;
        else
            obj->last = reference->prev;

        reference->prev->next = reference->next;
        return;
    }

    if(search_root(obj))
        return;

    obj->destructor(reference->ref);
    free(obj);
}

//TODO foolproofed versions (with NULL, prev set, etc.)