Function singlestep

third-party/lua-5.5.0/src/lgc.c:1617–1686

static l_mem singlestep (lua_State *L, int fast) {
  global_State *g = G(L);
  l_mem stepresult;
  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;
      stepresult = 1;
      break;
    }
    case GCSpropagate: {
      if (fast || g->gray == NULL) {
        g->gcstate = GCSenteratomic;  /* finish propagate phase */
        stepresult = 1;
      }
      else
        stepresult = propagatemark(g);  /* traverse one gray object */
      break;
    }
    case GCSenteratomic: {
      atomic(L);
      if (checkmajorminor(L, g))
        stepresult = step2minor;
      else {
        entersweep(L);
        stepresult = atomicstep;
      }
      break;
    }
    case GCSswpallgc: {  /* sweep "regular" objects */
      sweepstep(L, g, GCSswpfinobj, &g->finobj, fast);
      stepresult = GCSWEEPMAX;
      break;
    }
    case GCSswpfinobj: {  /* sweep objects with finalizers */
      sweepstep(L, g, GCSswptobefnz, &g->tobefnz, fast);
      stepresult = GCSWEEPMAX;
      break;
    }
    case GCSswptobefnz: {  /* sweep objects to be finalized */
      sweepstep(L, g, GCSswpend, NULL, fast);
      stepresult = GCSWEEPMAX;
      break;
    }
    case GCSswpend: {  /* finish sweeps */
      checkSizes(L, g);
      g->gcstate = GCScallfin;
      stepresult = GCSWEEPMAX;
      break;
    }
    case GCScallfin: {  /* call finalizers */
      if (g->tobefnz && !g->gcemergency && luaD_checkminstack(L)) {
        g->gcstopem = 0;  /* ok collections during finalizers */
        GCTM(L);  /* call one finalizer */
        stepresult = CWUFIN;
      }