Function singlestep

3rd/lua-5.4.3/src/lgc.c:1576–1636

static lu_mem singlestep (lua_State *L) {
  global_State *g = G(L);
  lu_mem work;
  lua_assert(!g->gcstopem);  /* collector is not reentrant */
  g->gcstopem = 1;  /* no emergency collections while collecting */
  switch (g->gcstate) {
    case GCSpause: {
      restartcollection(g);
      g->gcstate = GCSpropagate;
      work = 1;
      break;
    }
    case GCSpropagate: {
      if (g->gray == NULL) {  /* no more gray objects? */
        g->gcstate = GCSenteratomic;  /* finish propagate phase */
        work = 0;
      }
      else
        work = propagatemark(g);  /* traverse one gray object */
      break;
    }
    case GCSenteratomic: {
      work = atomic(L);  /* work is what was traversed by 'atomic' */
      entersweep(L);
      g->GCestimate = gettotalbytes(g);  /* first estimate */;
      break;
    }
    case GCSswpallgc: {  /* sweep "regular" objects */
      work = sweepstep(L, g, GCSswpfinobj, &g->finobj);
      break;
    }
    case GCSswpfinobj: {  /* sweep objects with finalizers */
      work = sweepstep(L, g, GCSswptobefnz, &g->tobefnz);
      break;
    }
    case GCSswptobefnz: {  /* sweep objects to be finalized */
      work = sweepstep(L, g, GCSswpend, NULL);
      break;
    }
    case GCSswpend: {  /* finish sweeps */
      checkSizes(L, g);
      g->gcstate = GCScallfin;
      work = 0;
      break;
    }
    case GCScallfin: {  /* call remaining finalizers */
      if (g->tobefnz && !g->gcemergency) {
        g->gcstopem = 0;  /* ok collections during finalizers */
        work = runafewfinalizers(L, GCFINMAX) * GCFINALIZECOST;
      }
      else {  /* emergency mode or no more finalizers */
        g->gcstate = GCSpause;  /* finish collection */
        work = 0;
      }
      break;
    }
    default: lua_assert(0); return 0;
  }