# Garbage Collection

---

## Object Definition

```c
typedef struct _kpl_gc {
    POOL_HEADER(_kpl_gc);
    union {
        _Atomic int32_t ref_count;
        _Atomic bool mark;
    } method;
    kpl_any any;
    pthread_mutex_t mutex;
} kpl_gc;

static _Atomic size_t gc_threads;

static kpl_gc *old_gc_head, *gc_head;
```

## Counting

`ref_count` starts at 1

Each assign increments the `ref_count`, each time it goes out of scope the `ref_count` is decreased

When `ref_count` hits 0, data is freed

## Tracing

1. Once triggered add a init task to the async queue
2. This task moves the `gc_head` to the `old_gc_head` and sets the `gc_wait` to off for each thread
3. Each thread will run down its queue queue marking found gc objects
3. Once all have run and `gc_threads == available_threads` add a mark and sweep task to the async queue
4. Async task goes down async queue and does final mark, then a sweep on the `old_gc_head` is done
5. What remains on the `old_gc_head` is added to `gc_head`