Function incstep

3rd/lua-5.4.3/src/lgc.c:1657–1673

** Performs a basic incremental step. The debt and step size are ** converted from bytes to "units of work"; then the function loops ** running single steps until adding that many units of work or ** finishing a cycle (pause state). Finally, it sets the debt that ** controls when next step will be performed. */

** controls when next step will be performed.
*/
static void incstep (lua_State *L, global_State *g) {
  int stepmul = (getgcparam(g->gcstepmul) | 1);  /* avoid division by 0 */
  l_mem debt = (g->GCdebt / WORK2MEM) * stepmul;
  l_mem stepsize = (g->gcstepsize <= log2maxs(l_mem))
                 ? ((cast(l_mem, 1) << g->gcstepsize) / WORK2MEM) * stepmul
                 : MAX_LMEM;  /* overflow; keep maximum value */
  do {  /* repeat until pause or enough "credit" (negative debt) */
    lu_mem work = singlestep(L);  /* perform one single step */
    debt -= work;
  } while (debt > -stepsize && g->gcstate != GCSpause);
  if (g->gcstate == GCSpause)
    setpause(g);  /* pause until next cycle */
  else {
    debt = (debt / stepmul) * WORK2MEM;  /* convert 'work units' to bytes */
    luaE_setdebt(g, debt);
  }
}

/*
** performs a basic GC step if collector is running