marCsweep/gc.c

#include <stdlib.h>

#include "gc.h"
#include "vm.h"

void mark(struct garbageObject *obj) {
  if (obj->mark) return;

  ++obj->mark;

  if (obj->type == GARBAGE_PAIR) {
    mark(obj->head);
    mark(obj->tail);
  }
}

void markAll(struct virtualMachine *vm) {
  for (int i = 0; i < vm->stackSize; ++i) {
    mark(vm->stack[i]);
  }
}

void sweep(struct virtualMachine *vm) {
  struct garbageObject **obj = &vm->head;

  while (*obj) {
    if (!(*obj)->mark) {
      struct garbageObject *unreachable = *obj;
      *obj = unreachable->next;
      free(unreachable);
      vm->refCount--;
    } else {
      (*obj)->mark = 0;
      obj = &(*obj)->next;
    }
  }
}

int collect(struct virtualMachine *vm) {
  int count = vm->refCount;
  markAll(vm);
  sweep(vm);
  vm->refMax = vm->refCount * 2;
  return count - vm->refCount;
}