CAMLprim value hh_mark_slice()

in src/heap/hh_shared.c [1091:1170]

• 56 lines of code
• 11 McCabe index (conditional complexity)

CAMLprim value hh_mark_slice(value work_val) {
  CAMLparam1(work_val);
  assert(info->gc_phase == Phase_mark);

  // We are able to partially scan an object for pointers and resume scanning in
  // a subsequent slice. This is useful in the event of large objects which
  // would otherwise cause long pauses if we needed to scan them all at once.
  //
  // If we stop in the middle of an object, we will store the address of that
  // object and the index of the field where we should resume. Otherwise, these
  // values will be NULL_ADDR and 0 respectively.
  static addr_t current_value = NULL_ADDR;
  static uintnat current_index = 0;

  intnat work = Long_val(work_val);
  intnat hashtbl_slots = info->hashtbl_slots;

  addr_t v;
  hh_header_t hd;
  hh_tag_t tag;
  uintnat i, size, start, end;

  // If the previous slice stopped in the middle of scanning an object, the
  // first thing we do in this slice is resume scanning where we left off.
  v = current_value;
  start = current_index;

  // Work through the mark stack, scanning all gray objects for pointers.
  // Because roots are colored gray but not added to the mark stack, also walk
  // the heap to find marked roots.
  while (work > 0) {
    if (v == NULL_ADDR && mark_stack_ptr > mark_stack) {
      v = *--mark_stack_ptr;
    }
    if (v != NULL_ADDR) {
      hd = Deref(v);
      tag = Obj_tag(hd);
      size = Obj_wosize_tag(hd, tag);
      if (tag == Entity_tag) {
        mark_entity(v);
        v = NULL_ADDR;
        start = 0;
      } else if (should_scan(tag)) {
        // Avoid scanning large objects all at once
        end = start + work;
        if (size < end) {
          end = size;
        }
        for (i = start; i < end; i++) {
          mark_slice_darken(Deref(Obj_field(v, i)));
        }
        if (end < size) {
          // We did not finish scanning this object. We will resume scanning
          // this object in the next slice.
          start = end;
        } else {
          v = NULL_ADDR;
          start = 0;
        }
      } else {
        v = NULL_ADDR;
      }
      work--;
    } else if (roots_ptr < hashtbl_slots) {
      // Visit roots in shared hash table
      mark_slice_darken(hashtbl[roots_ptr++].addr);
      work--;
    } else {
      // Done marking, transition to sweep phase.
      mark_stack_reset();
      info->gc_phase = Phase_sweep;
      break;
    }
  }

  current_value = v;
  current_index = start;

  CAMLreturn(Val_long(work));
}