#include "moar.h"

/* Gets a stable identifier for an object, which will not change even if the

 * GC moves the object. */

MVMuint64 MVM_gc_object_id(MVMThreadContext *tc, MVMObject *obj) {

    MVMuint64 id;

    /* If it's already in the old generation, just use memory address, as

     * gen2 objects never move. */

    if (obj->header.flags & MVM_CF_SECOND_GEN) {

        id = (MVMuint64)obj;

    }

    /* Otherwise, see if we already have a persistent object ID. */

    else {

        MVMObjectId *entry;

        uv_mutex_lock(&tc->instance->mutex_object_ids);

        if (obj->header.flags & MVM_CF_HAS_OBJECT_ID) {

            /* Has one, so just look up by address in the hash ID hash. */

            HASH_FIND(hash_handle, tc->instance->object_ids, (void *)&obj,

                sizeof(MVMObject *), entry);

        }

        else {

            /* Hasn't got one; allocate it a place in gen2 and make an entry

             * in the persistent object ID hash. */

            entry            = MVM_calloc(1, sizeof(MVMObjectId));

            entry->current   = obj;

            entry->gen2_addr = MVM_gc_gen2_allocate_zeroed(tc->gen2, obj->header.size);

            HASH_ADD_KEYPTR(hash_handle, tc->instance->object_ids, &(entry->current),

                sizeof(MVMObject *), entry);

            obj->header.flags |= MVM_CF_HAS_OBJECT_ID;

        }

        id = (MVMuint64)entry->gen2_addr;

        uv_mutex_unlock(&tc->instance->mutex_object_ids);

    }

    return id;

}

/* If an object with an entry here lives long enough to be promoted to gen2,

 * this removes the hash entry for it and returns the pre-allocated gen2

 * address. */

void * MVM_gc_object_id_use_allocation(MVMThreadContext *tc, MVMCollectable *item) {

    MVMObjectId *entry;

    void        *addr;

    uv_mutex_lock(&tc->instance->mutex_object_ids);

    HASH_FIND(hash_handle, tc->instance->object_ids, (void *)&item, sizeof(MVMObject *), entry);

    addr = entry->gen2_addr;

    HASH_DELETE(hash_handle, tc->instance->object_ids, entry);

    MVM_free(entry);

    item->flags ^= MVM_CF_HAS_OBJECT_ID;

    uv_mutex_unlock(&tc->instance->mutex_object_ids);

    return addr;

}

/* Clears hash entry for a persistent object ID when an object dies in the

 * nursery. */

void MVM_gc_object_id_clear(MVMThreadContext *tc, MVMCollectable *item) {

    MVMObjectId *entry;

    uv_mutex_lock(&tc->instance->mutex_object_ids);

    HASH_FIND(hash_handle, tc->instance->object_ids, (void *)&item, sizeof(MVMObject *), entry);

    HASH_DELETE(hash_handle, tc->instance->object_ids, entry);

    MVM_free(entry);

    uv_mutex_unlock(&tc->instance->mutex_object_ids);

}